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Sirtuins (SRTs) are a group of nicotinamide adenine dinucleotide (NAD+)‐dependent deacetylase that target both histone and nonhistone proteins. The biological function of SRT in horticultural plants has been rarely studied. In this study, FaSRT1‐2 was identified as a key member of the 8 FaSRTs encoded in cultivated strawberry genome. Transient overexpression of FaSRT1‐2 in strawberry fruit accelerated ripening, increased the content of anthocyanins and sugars, enhanced ripening‐related gene expression. Moreover, stable transformation of FaSRT1‐2 in strawberry plants resulted in enhanced vegetative growth, increased sensitivity to heat stress and increased susceptibility to Botrytis cinerea infection. Interestingly, knocking out the homologous gene in woodland strawberry had the opposite effects. Additionally, we found the content of stress‐related hormone abscisic acid (ABA) was decreased, while the growth‐related gibberellin (GA) concentration was increased in FaSRT1‐2 overexpression lines. Gene expression analysis revealed induction of heat shock proteins, transcription factors, stress‐related and antioxidant genes in the FaSRT1‐2‐overexpressed plants while knocked‐out of the gene had the opposite impact. In conclusion, our findings demonstrated that FaSRT1‐2 could positively promote strawberry plant vegetative growth and fruit ripening by affecting ABA and GA pathways. However, it negatively regulates the resistance to heat stress and B. cinerea infection by influencing the related gene expression. Summary statement: FaSRT1‐2 is likely to exert a positive regulatory effect on both strawberry fruit ripening and vegetative growth by stimulating sugar, anthocyanin, and the gibberellin metabolism pathway. Moreover, FaSRT1‐2 appears to enhance the susceptibility of strawberry plants to heat stress while also promoting defence against Botrytis cinerea through alterations in abscisic acid metabolism and stress‐related genes expression. [ABSTRACT FROM AUTHOR]

The circadian clock plays multiple functions in the regulation of plant growth, development and response to various abiotic stress. Here, we showed that the core oscillator component late elongated hypocotyl (LHY) was involved in rice response to salt stress. The mutations of OsLHY gene led to reduced salt tolerance in rice. Transcriptomic analyses revealed that the OsLHY gene regulates the expression of genes related to ion homeostasis and the abscisic acid (ABA) signalling pathway, including genes encoded High‐affinity K+ transporters (OsHKTs) and the stress‐activated protein kinases (OsSAPKs). We demonstrated that OsLHY directly binds the promoters of OsHKT1;1, OsHKT1;4 and OsSAPK9 to regulate their expression. Moreover, the ossapk9 mutants exhibited salt tolerance under salt stress. Taken together, our findings revealed that OsLHY integrates ion homeostasis and the ABA pathway to regulate salt tolerance in rice, providing insights into our understanding of how the circadian clock controls rice response to salt stress. Summary statement: The expression of rice core component circadian clock gene LATE ELONGATED HYPOCOTYL can be induced under salt stress, which alters the expression of Na+ and K+ transporter related genes and genes in the ABA signalling pathway to positively regulate salt stress tolerance in rice. [ABSTRACT FROM AUTHOR]

Cold stress is a major meteorological threat to crop growth and yield. Abscisic acid (ABA) plays important roles in plant cold tolerance by activating the expression of cold‐responsive genes; however, the underlying transcriptional regulatory module remains unknown. Here, we demonstrated that the cold‐ and ABA‐responsive transcription factor ETHYLENE RESPONSE FACTOR 15 (ERF15) positively regulates ABA‐mediated cold tolerance in tomato. Exogenous ABA treatment significantly enhanced cold tolerance in wild‐type tomato plants but failed to rescue erf15 mutants from cold stress. Transcriptome analysis showed that ERF15 was associated with the expression of cold‐responsive transcription factors such as CBF1 and WRKY6. Further RT‐qPCR assays confirmed that the ABA‐induced increased in CBF1 and WRKY6 transcripts was suppressed in erf15 mutants when the plants were subjected to cold treatment. Moreover, yeast one‐hybrid assays, dual‐luciferase assays and electrophoretic mobility shift assays demonstrated that ERF15 activated the transcription of CBF1 and WRKY6 by binding their promoters. Silencing CBF1 or WRKY6 significantly decreased cold tolerance. Overall, our study identified the role of ERF15 in conferring ABA‐mediated cold tolerance in tomato plants by activating CBF1 and WRKY6 expression. This study not only broadens our knowledge of the mechanism of ABA‐mediated cold tolerance in plants but also highlights ERF15 as an ideal target gene for cold‐tolerant crop breeding. Summary statement: This study demonstrated that the cold‐ and abscisic acid (ABA)‐responsive transcription factor ETHYLENE RESPONSE FACTOR 15 positively regulates ABA‐mediated cold tolerance in tomato plants by activating CBF1 and WRKY6 expression. [ABSTRACT FROM AUTHOR]

Sesuvium portulacastrum (L.) is a halophyte, adapted to grow naturally under saline environments. The ability to use Na and K interchangeably indicated its facultative halophyte nature. No significant growth reduction occurs in seedlings up to 250 mM NaCl, except for curling of the youngest leaf. Within 8 h of salt treatment, seedlings accumulate proline, glycine betaine and other amino acids in both root and shoot. Despite a continued increase of tissue Na content, the number of differentially expressed genes (DEGs) decreases between 8 and 24 h of salt exposure, indicating transcriptional restoration after the initial osmotic challenge. At 8 h, upregulated genes mainly encode transporters and transcription factors, while genes in growth‐related pathways such as photosynthesis and ribosome‐associated biogenesis are suppressed. Overexpression of SpRAB18 (an ABA‐responsive dehydrin), one of the most strongly induced DEGs, in soybean was found to increase biomass in control conditions and the growth benefit was maintained when plants were grown in 100 mM NaCl, indicating conservation of function in halophyte and glycophyte. An open‐access transcriptome database "SesuviumKB" (https://cb.imsc.res.in/sesuviumkb/) was developed to involve the scientific community in wide‐scale functional studies of S. portulacastrum genes, that could pave the way to engineer salt tolerance in crops. Summary Statement: We provide data on the physiology, transcriptome and metabolome of the halophyte Sesuvium portulacastrum (L.). An open acccess database "SesuviumKB" was constructed to facilitate data access and enable future wide‐scale functional testing of the genes through the community. [ABSTRACT FROM AUTHOR]

The phytohormone abscisic acid (ABA) is synthesised by plants during drought to close stomata and regulate desiccation tolerance pathways. Conifers and some angiosperms with embolism‐resistant xylem show a peaking‐type (p‐type) response in ABA levels, in which ABA levels increase early in drought then decrease as drought progresses, declining to pre‐stressed levels. The mechanism behind this dynamic remains unknown. Here, we sought to characterise the mechanism driving p‐type ABA dynamics in the conifer Callitris rhomboidea and the highly drought‐resistant angiosperm Umbellularia californica. We measured leaf water potentials (Ψl), stomatal conductance, ABA, conjugates and phaseic acid (PA) levels in potted plants during a prolonged but non‐fatal drought. Both species displayed a p‐type ABA dynamic during prolonged drought. In branches collected before and after the peak in endogenous ABA levels in planta, that were rehydrated overnight and then bench dried, ABA biosynthesis was deactivated beyond leaf turgor loss point. Considerable conversion of ABA to conjugates was found to occur during drought, but not catabolism to PA. The mechanism driving the decline in ABA levels in p‐type species may be conserved across embolism‐resistant seed plants and is mediated by sustained conjugation of ABA and the deactivation of ABA accumulation as Ψl becomes more negative than turgor loss. Summary Statement: We find that abscisic acid biosynthesis is deactivated after leaf turgor loss point during extreme drought, but that the conjugation of ABA to inactive forms remains constant, leading to a decline in ABA levels in embolism‐resistant species. [ABSTRACT FROM AUTHOR]

Hydrotropism is an important adaptation of plant roots to the uneven distribution of water, with current research mainly focused on Arabidopsis thaliana. To examine hydrotropism in tomato (Solanum lycopersicum) primary roots, we used RNA sequencing to determine gene expression of root tips (apical 5 mm) on dry and wet sides of hydrostimulated roots grown on agar plates. Hydrostimulation enhances cell division and expansion on the dry side compared with the wet side of the root tip. In hydrostimulated roots, the abscisic acid (ABA) biosynthesis gene ABA4 was induced more on the dry than the wet side of root tips. The ABA biosynthesis inhibitor Fluridone and the ABA‐deficient mutant notabilis (not) significantly decreased hydrotropic curvature. Wild‐type, but not the ABA biosynthesis mutant not, root tips showed asymmetric H+ efflux, with greater efflux on the dry than on the wet side of root tips. Thus, ABA mediates asymmetric H+ efflux, allowing the root to bend towards the wet side to take up more water. Summary statement: ABA regulates asymmetric H+ efflux, which is required for the root hydrotropic bending. [ABSTRACT FROM AUTHOR]

Wheat (Triticum aestivum L.) is an important food crop mainly grown in arid and semiarid regions worldwide, whose productivity is severely limited by drought stress. Although various E3 ubiquitin (Ub) ligases regulate drought stress, only a few SINA‐type E3 Ub ligases are known to participate in such responses. Herein, we identified and cloned 15 TaSINAs from wheat. The transcription level of TaSINA2B was highly induced by drought, osmotic and abscisic acid treatments. Two‐type promoters of TaSINA2B were found in 192 wheat accessions; furthermore wheat accessions with promoter TaSINA2BII showed a considerably higher level of drought tolerance and gene expression levels than those characterizing accessions with promoter TaSINA2BI that was mainly caused by a 64 bp insertion in its promoter. Enhanced drought tolerance of TaSINA2B‐overexpressing (OE) transgenic wheat lines was found to be associated with root growth promotion. Further, an interaction between TaSINA2B and TaSINA1D was detected through yeast two‐hybrid and bimolecular fluorescence complementation assays. And TaSINA1D‐OE transgenic wheat lines showed similar drought tolerance and root growth phenotype to those observed when TaSINA2B was overexpressed. Therefore, the variation of TaSINA2B promoter contributed to the drought stress regulation, while TaSINA2B, interacting with TaSINA1D, positively regulated drought tolerance by promoting root growth. Summary Statement: TaSINA2B is closely associated to drought tolerance, and the 64 bp insertion in promoter drives the enhanced expression of TaSINA2B. TaSINA2B interact with TaSINA1D, both of which positively regulates drought tolerance and root growth in wheat. [ABSTRACT FROM AUTHOR]

Cold is a major environmental factor that restrains potato production. Abscisic acid (ABA) can enhance freezing tolerance in many plant species, but powerful evidence of the ABA‐mediated signalling pathway related to freezing tolerance is still in deficiency. In the present study, cold acclimation capacity of the potato genotypes was enhanced alongside with improved endogenous content of ABA. Further exogenous application of ABA and its inhibitor (NDGA) could enhance and reduce potato freezing tolerance, respectively. Moreover, expression pattern of downstream genes in ABA signalling pathway was analysed and only ScAREB4 was identified with specifically upregulate in S. commersonii (CMM5) after cold and ABA treatments. Transgenic assay with overexpression of ScAREB4 showed that ScAREB4 promoted freezing tolerance. Global transcriptome profiling indicated that overexpression of ScAREB4 induced expression of TPS9 (trehalose‐6‐phosphate synthase) and GSTU8 (glutathione transferase), in accordance with improved TPS activity, trehalose content, higher GST activity and accumulated dramatically less H2O2 in the ScAREB4 overexpressed transgenic lines. Taken together, the current results indicate that increased endogenous content of ABA is related to freezing tolerance in potato. Moreover, ScAREB4 functions as a downstream transcription factor of ABA signalling to promote cold tolerance, which is associated with increased trehalose content and antioxidant capacity. Summary Statement: The cold acclimation capacity of the potato genotypes was enhanced alongside with improved endogenous content of ABA and ScAREB4 was identified to promotes potato constitutive and acclimated freezing tolerance. [ABSTRACT FROM AUTHOR]

Heat stress has a negative impact on pollen development in maize (Zea mays L.) but the postpollination events that determine kernel sterility are less well characterised. The impact of short‐term (hours) heat exposure during postpollination was therefore assessed in silks and ovaries. The temperatures inside the kernels housed within the husks was significantly lower than the imposed heat stress. This protected the ovaries and possibly the later phase of pollen tube growth from the adverse effects of heat stress. Failure of maize kernel fertilization was observed within 6 h of heat stress exposure postpollination. This was accompanied by a significant restriction of early pollen tube growth rather than pollen germination. Limitations on early pollen tube growth were therefore a major factor contributing to heat stress‐induced kernel sterility. Exposure to heat stress altered the sugar composition of silks, suggesting that hexose supply contributed to the limitations on pollen tube growth. Moreover, the activities of sucrose metabolising enzymes, the expression of sucrose degradation and trehalose biosynthesis genes were decreased following heat stress. Significant increases in reactive oxygen species, abscisic acid and auxin levels accompanied by altered expression of phytohormone‐related genes may also be important in the heat‐induced suppression of pollen tube growth. Summary statement: Just 6 h of postpollination heat stress exposure was solely responsible for failure in maize. Heat stress altered sugar composition, increased ABA and auxin and higher reactive oxygen species accumulation in silks, negatively impacts pollen tube growth. [ABSTRACT FROM AUTHOR]

Plants have developed various defense mechanisms against environmental stresses by regulating hormone signaling. Jasmonic acid (JA) is a major phytohormone associated with plant defense responses. JASMONATE ZIM‐DOMAIN (JAZ) proteins play a regulatory role in repressing JA signaling, impacting plant responses to both biotic and abiotic stresses. Here, we isolated 7 JAZ genes in pepper and selected CA03g31030, a Capsicum annuum JAZ1‐03 (CaJAZ1‐03) gene, for further study based on its expression level in response to abiotic stresses. Through virus‐induced gene silencing (VIGS) in pepper and overexpression in transgenic Arabidopsis plants, we established the functional role of CaJAZ1‐03. Functional studies revealed that CaJAZ1‐03 dampens abscisic acid (ABA) signaling and drought stress responses. The cell‐free degradation assay showed faster degradation of CaJAZ1‐03 in drought‐ or ABA‐treated pepper leaves compared to healthy leaves. Conversely, CaJAZ1‐03 was completely preserved under MG132 treatment, indicating that CaJAZ1‐03 stability is modulated via the ubiquitin‐26s proteasome pathway. We also found that the pepper RING‐type E3 ligase CaASRF1 interacts with and ubiquitinates CaJAZ1‐03. Additional cell‐free degradation assays revealed a negative correlation between CaJAZ1‐03 and CaASRF1 expression levels. Collectively, these findings suggest that CaJAZ1‐03 negatively regulates ABA signaling and drought responses and that its protein stability is modulated by CaASRF1. Summary statement: Previous studies reported that JASMONATE ZIM‐DOMAIN (JAZ) proteins function as the key suppressors in the Jasmonic acid signaling pathway. Here, we identified pepper JAZ protein CaJAZ1‐03, which plays a negative role in abscisic acid signaling and drought stress responses, and its protein stability is modulated by pepper RING‐type E3 ligase CaASRF1. [ABSTRACT FROM AUTHOR]

Drought resistance is essential for plant production under water‐limiting environments. Abscisic acid (ABA) plays a critical role in stomata but its impact on hydraulic function beyond the stomata is far less studied. We selected genotypes differing in their ability to accumulate ABA to investigate its role in drought‐induced dysfunction. All genotypes exhibited similar leaf and stem embolism resistance regardless of differences in ABA levels. Their leaf hydraulic resistance was also similar. Differences were only observed between the two extreme genotypes: sitiens (sit; a strong ABA‐deficient mutant) and sp12 (a transgenic line that constitutively overaccumulates ABA), where the water potential inducing 50% embolism was 0.25 MPa lower in sp12 than in sit. Maximum stomatal and minimum leaf conductances were considerably lower in plants with higher ABA (wild type [WT] and sp12) than in ABA‐deficient mutants. Variations in gas exchange across genotypes were associated with ABA levels and differences in stomatal density and size. The lower water loss in plants with higher ABA meant that lethal water potentials associated with embolism occurred later during drought in sp12 plants, followed by WT, and then by the ABA‐deficient mutants. Therefore, the primary pathway by which ABA enhances drought resistance is via declines in water loss, which delays dehydration and hydraulic dysfunction. Summary statement: The impact of abscisic acid on the drought tolerance of young plants of tomato is essentially associated with stomatal function, and not with xylem resistance to embolism. [ABSTRACT FROM AUTHOR]

The natural variation between Arabidopsis (Arabidopsis thaliana) ecotypes Columbia (Col) and Landsberg erecta (Ler) strongly affects abscisic acid (ABA) signalling and drought tolerance. Here, we report that the cysteine‐rich receptor‐like protein kinase CRK4 is involved in regulating ABA signalling, which contributes to the differences in drought stress tolerance between Col‐0 and Ler‐0. Loss‐of‐function crk4 mutants in the Col‐0 background were less drought tolerant than Col‐0, whereas overexpressing CRK4 in the Ler‐0 background partially to completely restored the drought‐sensitive phenotype of Ler‐0. F1 plants derived from a cross between the crk4 mutant and Ler‐0 showed an ABA‐insensitive phenotype with respect to stomatal movement, along with reduced drought tolerance like Ler‐0. We demonstrate that CRK4 interacts with the U‐box E3 ligase PUB13 and enhances its abundance, thus promoting the degradation of ABA‐INSENSITIVE 1 (ABI1), a negative regulator of ABA signalling. Together, these findings reveal an important regulatory mechanism for modulating ABI1 levels by the CRK4‐PUB13 module to fine‐tune drought tolerance in Arabidopsis. Summary statement: CRK4, contributing to the drought stress difference between Col‐0 and Ler, interacts with and enhances the protein levels of the U‐box E3 ligase PUB13, which promotes the degradation of ABI1 (ABA‐INSENSITIVE 1), thus positively regulating ABA‐mediated stomatal movements and drought stress tolerance. [ABSTRACT FROM AUTHOR]

Herbivore‐induced plant defence responses share common components with plant responses to abiotic stresses. However, whether abiotic stress‐responsive factors influence the resistance of plants to herbivores by regulating these components remains largely unknown. Here, we cloned a dehydration‐responsive element‐binding gene in rice, OsDREB1A, and investigated its role in the resistance of rice to the phloem‐feeding herbivore, brown planthopper (BPH, Nilaparvata lugens), under normal and low temperatures. We found that OsDREB1A localized to the nucleus, and its transcripts in rice were up‐regulated in response to BPH infestation, low temperatures and treatment with methyl jasmonate or salicylic acid. Silencing OsDREB1A changed transcript levels of two defence‐related WRKY and two PLD genes, enhanced levels of jasmonic acid (JA), JA‐isoleucine and abscisic acid, and decreased the ethylene level in rice; these changes subsequently enhanced the resistance of plants to BPH, especially at 17°C, by decreasing the hatching rate and delaying the development of BPH eggs. Moreover, silencing OsDREB1A increased the growth of rice plants. These findings suggest that OsDREB1A, which positively regulates the resistance of rice to abiotic stresses, negatively regulates the resistance of rice to BPH. Summary statement: OsDREB1A, a positive modulator of rice tolerance to abiotic stress, negatively regulates the resistance of rice to BPH by influencing the biosynthesis of jasmonic acid (JA), JA‐isoleucine, abscisic acid, and ethylene. Brown planthopper appears able to use OsDREB1A to benefit itself by suppressing rice defences and resisting abiotic stresses. [ABSTRACT FROM AUTHOR]

While variation in mean annual precipitation (MAP) of the native habitat of a species has been shown to determine the ability of a species to resist a hydraulic decrease during drought, it remains unknown whether these variations in MAP also influence the ability of a species to recover and survive drought. Leaf hydraulic and gas exchange recovery following drought and the underlying mechanisms of these responses in six Caragana species from habitats along a large precipitation gradient were investigated during rehydration in a common garden. The gas exchange of species from arid habitats recovered more rapidly during rehydration after mild, moderate and severe drought stress treatments than species from humid habitats. The recovery of gas exchange was not associated with foliar abscisic acid concentration, but tightly related to the recovery of leaf hydraulic conductance (Kleaf). The recovery of Kleaf was associated with the loss of Kleaf during dehydration under mild and moderate drought stress, and to leaf xylem embolism formation under severe drought stress. Results pointed to the different ability to recover in gas exchange in six Caragana species post‐drought is associated with the MAP of the species in its native habitat. Summary Statement: Mean annual precipitation (MAP) has been shown to shape species' ability to resist a hydraulic dysfunction during drought. Our findings suggest that the ability to recover in gas exchange post‐drought as a strong driver in shaping species' distribution along a MAP gradient. [ABSTRACT FROM AUTHOR]

The mitogen‐activated protein kinase (MAPK) pathway is an important signalling event associated with every aspect of plant growth, development, yield, abiotic and biotic stress adaptation. Being a central metabolic pathway, it is a vital target for manipulation for crop improvement. In this review, we have summarised recent advancements in understanding involvement of MAPK signalling in modulating abiotic and biotic stress tolerance, architecture and yield of plants. MAPK signalling cross talks with reactive oxygen species (ROS) and abscisic acid (ABA) signalling events in bringing about abiotic stress adaptation in plants. The intricate involvement of MAPK pathway with plant's pathogen defence ability has also been identified. Further, recent research findings point towards participation of MAPK signalling in shaping plant architecture and yield. These make MAPK pathway an important target for crop improvement and we discuss here various strategies to tweak MAPK signalling components for designing future crops with improved physiology and phenotypes. Summary Statement: To the best of our knowledge, the proposed review article is first of its kind which has comprehensively discussed involvement of mitogen‐activated protein kinase (MAPK) signalling cascade in abiotic and biotic stress tolerance as well as plant development and crop yield in a single article. Additionally, one of the novel features of this review is that it has also discussed the ways to manipulate the MAPK signalling components for designing crops for improved stress resilience as well as yield. Climate change, rapid decline in lands arable lands and population explosion necessitates revisiting the role of a very important central metabolic pathway (i.e., MAPK signalling module) for achieving crop improvement and stress adaption in plants and in our present review; we have tried to address it to the best possible extent. [ABSTRACT FROM AUTHOR]

Endodormancy (ED) is a crucial stage in the life cycle of many perennial plants. ED release requires accumulating a certain amount of cold exposure, measured as chilling units. However, the mechanism governing the effect of chilling on ED duration is poorly understood. We used the potato tuber model to investigate the response to chilling as associated with ED release. We measured the accumulation of specific sugars during and after chilling, defined as sugar units. We discovered that ED duration correlated better with sugar units accumulation than chilling units. A logistic function was developed based on sugar units measurements to predict ED duration. Knockout or overexpression of the vacuolar invertase gene (StVInv) unexpectedly modified sugar units levels and extended or shortened ED, respectively. Silencing the energy sensor SNF1‐related protein kinase 1, induced higher sugar units accumulation and shorter ED. Sugar units accumulation induced by chilling or transgenic lines reduced plasmodesmal (PD) closure in the dormant bud meristem. Chilling or knockout of abscisic acid (ABA) 8′‐hydroxylase induced ABA accumulation, in parallel to sweetening, and antagonistically promoted PD closure. Our results suggest that chilling induce sugar units and ABA accumulation, resulting in antagonistic signals for symplastic connection of the dormant bud. Summary statement: Endodormancy (ED) duration of potato tuber correlates better with soluble sugars accumulation (sugar units) than chilling units. Chilling induces sugar units and ABA accumulation, resulting in antagonistic signals for symplastic connection of the dormant bud, determining ED duration. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) signalling triggers drought resistance mediated by SNF1‐related kinase 2s (SnRK2s), which transmits stress signals through the phosphorylation of several downstream factors. However, these kinases and their downstream targets remain elusive in pepper plants. This study aimed to isolate interacting partners of CaSnRK2.6, a homologue of Arabidopsis SnRK2.6/OST1. Among the candidate proteins, we identified a homeodomain‐leucine zipper (HD‐Zip) class II protein and named it CaHAT1 (Capsicum annuum homeobox ABA signalling related‐ transcription factor 1). CaHAT1‐silenced pepper and ‐overexpression (OE) transgenic Arabidopsis plants were generated to investigate the in vivo function of CaHAT1 in drought response. Following the application of drought stress, CaHAT1‐silenced pepper plants exhibited drought‐sensitive phenotypes with reduced ABA‐mediated stomatal closure and lower expression of stress‐responsive genes compared with control plants. In contrast, CaHAT1‐OE transgenic Arabidopsis plants showed the opposite phenotypes, including increased drought resistance and ABA sensitivity. CaHAT1, particularly its N‐terminal consensus sequences, was directly phosphorylated by CaSnRK2.6. Furthermore, CaSnRK2.6 kinase activity and CaSnRK2.6‐mediated CaHAT1 phosphorylation levels were enhanced by treatment with ABA and drought stress. Taken together, our results indicated that CaHAT1, which is the target protein of CaSnRK2.6, is a positive regulator of drought stress response. This study advances our understanding of CaHAT1–CaSnRK2.6 mediated defence mechanisms in pepper plants against drought stress. Summary Statement: We previously reported that pepper SnRK2 type kinase CaSnRK2.6 functions as a positive modulator of abscisic acid (ABA) signalling and drought response. Building on this in the present study, we identified the homeodomain‐leucine zipper class II protein CaHAT1 as a substrate of CaSnRK2.6, which plays a positive role in the regulation of drought stress response via ABA‐mediated signalling. [ABSTRACT FROM AUTHOR]

Gladiolus hybridus is one of the most popular flowers worldwide. However, its corm dormancy characteristic largely limits its off‐season production. Long‐term cold treatment (LT), which increases sugar content and reduces abscisic acid (ABA), is an efficient approach to accelerate corm dormancy release (CDR). Here, we identified a GhbZIP30‐GhCCCH17 module that mediates the antagonism between sugars and ABA during CDR. We showed that sugars promoted CDR by reducing ABA levels in Gladiolus. Our data demonstrated that GhbZIP30 transcription factor directly binds the GhCCCH17 zinc finger promoter and activates its transcription, confirmed by yeast one‐hybrid, dual‐luciferase (Dual‐LUC), chromatin immunoprecipitation‐quantitative PCR (ChIP‐qPCR) and electrophoretic mobility shift assay (EMSA). GhCCCH17 is a transcriptional activator, and its nuclear localisation is altered by surcose and cytokinin treatments. Both GhbZIP30 and GhCCCH17 positively respond to LT, sugars, and cytokinin treatments. Silencing GhbZIP30 or GhCCCH17 resulted in delayed CDR by regulating ABA metabolic genes, while their overexpression promoted CDR. Taken together, we propose that the GhbZIP30‐GhCCCH17 module is involved in cold‐ and glucose‐induced CDR by regulating ABA metabolic genes. Brief Summary: Sugars are regarded as integrators of environmental and endogenous signals. However, the relationship between abscisic acid (ABA) and sugars in the process of geophyte dormancy release is still unclear. In this study, we demonstrated that glucose plays a positive role in CDR in Gladiolus by decreasing endogenous ABA. We propose a GhbZIP30‐GhCCCH17 module that mediates the antagonism between sugars and ABA during CDR by regulating ABA metabolic genes. Significance Statement: During cold storage of Gladiolus cormels, endogenous glucose and sucrose levels increase, which repress endogenous abscisic acid (ABA) and contribute to corm dormancy release (CDR). During this process, GhbZIP30 directly binds the GhCCCH17 promoter and activates its transcription. The GhbZIP30‐GhCCCH17 module is involved in cold‐ and glucose‐induced CDR by regulating ABA metabolic genes. [ABSTRACT FROM AUTHOR]

SR proteins are conserved RNA‐binding proteins best known as splicing regulators that have also been implicated in other steps of gene expression. Despite mounting evidence for a role in plant development and stress responses, the molecular pathways underlying SR protein regulation of these processes remain poorly understood. Here we show that the plant‐specific SCL30a SR protein negatively regulates ABA signaling to control seed traits and stress responses during germination in Arabidopsis. Transcriptome‐wide analyses revealed that loss of SCL30a function barely affects splicing, but largely induces ABA‐responsive gene expression and genes repressed during germination. Accordingly, scl30a mutant seeds display delayed germination and hypersensitivity to ABA and high salinity, while transgenic plants overexpressing SCL30a exhibit reduced ABA and salt stress sensitivity. An ABA biosynthesis inhibitor rescues the enhanced mutant seed stress sensitivity, and epistatic analyses confirm that this hypersensitivity requires a functional ABA pathway. Finally, seed ABA levels are unchanged by altered SCL30a expression, indicating that the gene promotes seed germination under stress by reducing sensitivity to the phytohormone. Our results reveal a new player in ABA‐mediated control of early development and stress response. Summary statement: We found that an Arabidopsis SR protein represses ABA‐induced gene expression to modulate seed traits and germination. Our results uncover a new player in ABA‐mediated control of early plant development and stress responses. [ABSTRACT FROM AUTHOR]

Chilling can decrease stomatal sensitivity to abscisic acid (ABA) in some legumes, although hormonal mechanisms involved are unclear. After evaluating leaf gas exchange of 16 European soybean genotypes at 14°C, 6 genotypes representing the range of response were selected. Further experiments combined low (L, 14°C) and high (H, 24°C) temperature exposure from sowing until the unifoliate leaf was visible and L or H temperature until full leaf expansion, to impose four temperature treatments: LL, LH, HL, and HH. Prolonged chilling (LL) substantially decreased leaf water content but increased leaf ethylene evolution and foliar concentrations of the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid, indole‐3‐acetic acid, ABA and jasmonic acid. Across genotypes, photosynthesis linearly increased with stomatal conductance (Gs), with photosynthesis of HH plants threefold higher than LL plants at the same Gs. In all treatments except LL, Gs declined with foliar ABA accumulation. Foliar ABA sprays substantially decreased Gs of HH plants, but did not significantly affect LL plants. Thus low temperature compromised stomatal sensitivity to endogenous and exogenous ABA. Applying the ethylene antagonist 1 methyl‐cyclopropene partially reverted excessive stomatal opening of LL plants. Thus, chilling‐induced ethylene accumulation may mediate stomatal insensitivity to ABA, offering chemical opportunities for improving seedling survival in cold environments. Summary statement: Prolonged chilling of soybean increased foliar ethylene evolution, abscisic acid concentrations and stomatal conductance resulting in extremely low leaf water contents. Applying the ethylene antagonist 1‐MCP partially reversed this maladaptive stomatal response. [ABSTRACT FROM AUTHOR]

Salt stress is a major environmental factor limiting crop growth and productivity. Here, we show that Salt‐Tolerant Gene 1 (ZmSTG1) contributes to salt tolerance by maintaining photosystem activity in maize. ZmSTG1 encodes an endoplasmic reticulum localized protein and retrotransposon insertion in the promoter region causes differential expression levels in maize inbred lines. Overexpression of ZmSTG1 improved plant growth vigor, and knockout of ZmSTG1 weakened plant growth under normal and salt stress conditions. Transcriptome and metabolome analyses indicated that ZmSTG1 might regulate the expression of lipid trafficking‐related genes dependent on the abscisic acid (ABA) signaling pathway, thereby increasing the galactolipids and phospholipid concentrations in the photosynthetic membrane under salt stress. Chlorophyll fluorescence parameters showed that the knockout of ZmSTG1 led to significant impairment of plant photosystem II (PSII) activity under normal and salt stress conditions, whereas overexpression of ZmSTG1 dramatically improved plant PSII activity under salt stress conditions. We also demonstrated that the application of the salt‐tolerant locus could enhance salt tolerance in hybrid maize plants. Taken together, we propose that ZmSTG1 may modulate the lipid composition in the photosynthetic membrane by affecting the expression of lipid trafficking‐related genes to maintain the photosynthetic activity of plants under salt stress. Summary Statement: The identification and use of tolerance genes to alleviate the damage caused by salt stress is an effective strategy for crop genetic improvement. Salt‐Tolerant Gene 1 (ZmSTG1) contributes to salt tolerance by maintaining the photosystem activity in maize. The ZmSTG1‐mediated salt stress response can be achieved by modulating the expression of genes associated with lipid trafficking processes and is dependent on the ABA signaling pathway. [ABSTRACT FROM AUTHOR]

Perennial para‐ and endo‐dormancy are seasonally separate phenomena. Whereas para‐dormancy is the suppression of axillary buds (AXBs) by a growing shoot, endo‐dormancy is the short‐day elicited arrest of terminal and AXBs. In hybrid aspen (Populus tremula x P. tremuloides) compromising the apex releases para‐dormancy, whereas endo‐dormancy requires chilling. ABA and GA are implicated in both phenomena. To untangle their roles, we blocked ABA biosynthesis with fluridone (FD), which significantly reduced ABA levels, downregulated GA‐deactivation genes, upregulated the major GA3ox‐biosynthetic genes, and initiated branching. Comprehensive GA‐metabolite analyses suggested that FD treatment shifted GA production to the non‐13‐hydroxylation pathway, enhancing GA4 function. Applied ABA counteracted FD effects on GA metabolism and downregulated several GA3/4‐inducible α‐ and γ‐clade 1,3‐β‐glucanases that hydrolyze callose at plasmodesmata (PD), thereby enhancing PD‐callose accumulation. Remarkably, ABA‐deficient plants repressed GA4 biosynthesis and established endo‐dormancy like controls but showed increased stress sensitivity. Repression of GA4 biosynthesis involved short‐day induced DNA methylation events within the GA3ox2 promoter. In conclusion, the results cast new light on the roles of ABA and GA in dormancy cycling. In para‐dormancy, PD‐callose turnover is antagonized by ABA, whereas in short‐day conditions, lack of GA4 biosynthesis promotes callose deposition that is structurally persistent throughout endo‐dormancy. Summary statement: This study untangles the so far undetermined nature of para‐ and endo‐dormancy. Using the model tree hybrid aspen, we show that para‐dormancy is caused by ABA antagonizing GA4, whereas endo‐dormancy is due to repression of GA4 biosynthesis, likely by short‐day induced methylation of the GA3ox2 promoter. [ABSTRACT FROM AUTHOR]

High temperatures (HT) cause pollen abortion and poor floret fertility in rice, which is closely associated with excessive accumulation of reactive oxygen species (ROS) in the developing anthers. However, the relationships between accumulation of abscisic acid (ABA) and ROS, and their effects on tapetum‐specific programmed cell death (PCD) in HT‐stressed anthers are poorly characterised. Here, we determined the spatiotemporal changes in ABA and ROS levels, and their relationships with tapetal PCD under HT exposure. Mutants lacking ABA‐activated protein kinase 2 (SAPK2) functions and exogenous ABA treatments were used to explore the effects of ABA signalling on the induction of PCD and ROS accumulation during pollen development. HT‐induced pollen abortion was tightly associated with ABA accumulation and oxidative stress. The higher ABA level in HT‐stressed anthers resulted in the earlier initiation of PCD induction and subsequently abnormal tapetum degeneration by activating ROS accumulation in developing anthers. Interactions between SAPK2 and DEAD‐box ATP‐dependent RNA helicase elF4A‐1 (RH4) were required for ABA‐induced ROS generation in developing anthers. The OsSAPK2 knockout mutants showed the impaired PCD responses in the absence of HT. However, the deficiency of SAPK2 functions did not suppress the ABA‐mediated ROS generation in HT‐stressed anthers. Summary statement: High temperatures (HT) disturbed the cellular distributions of ABA and ROS contents in rice anthers. The higher ABA in HT‐stressed anthers contributed to HT‐induced pollen abortion by activating ROS generation and oxidation in developing anthers. Interactions between SAPK2 and DEAD‐box ATP‐dependent RNA helicase elF4A‐1 (RH4) were required for ABA‐induced ROS generation during pollen development and its response to HT exposure. [ABSTRACT FROM AUTHOR]

Low light stress seriously decreased wheat grain number through the formation of aborted spike during the reproductive period and induced new tiller regeneration to offset the loss of grain number. However, the mechanism by which plants coordinate spike aborted growth and the regeneration of new tillers remains unknown. To better understand this coordinated process, morphological, physiological and transcriptomic analyses were performed under low light stress at the young microspore stage. Our findings indicated that leaves exhausted most stored carbohydrates in 1 day of darkness. However, spike and uppermost internode (UI) were converted from sink to source, due to increased abscisic acid (ABA) content and decreased cytokinin content. During this process, genes encoding amylases, Sugars Will Eventually be Exported Transporters (SWEET) and sucrose transporters or sucrose carriers (SUT/SUC) were upregulated in spike and UI, which degraded starch into soluble sugars and loaded them into the phloem. Subsequently, soluble sugars were transported to tiller node (TN) where cytokinin and auxin content increased and ABA content decreased, followed by unloading into TN cells by upregulated cell wall invertase (CWINV) genes and highly expressed H+/hexose symporter genes. Finally, expansin genes integrated the sugar pathway and hormone pathway, and regulate the formation of new tillers directly. Summary Statement: Low light stress changed source–sink relationship by regulating the expression of sugar metabolism genes and sugar transport genes as well as hormone content in spike, uppermost internode and tiller node. Meanwhile, expansin genes integrated the sugar pathway and hormone pathway and regulated the formation of new tillers. [ABSTRACT FROM AUTHOR]

Preharvest sprouting (PHS) is an unfavorable trait in cereal crops and causes serious yield loss. However, the molecular mechanism underlying PHS remains largely elusive. Here, we identified a member of 9‐cis‐epoxycarotenoid dioxygenase family, OsNCED3, which regulates PHS and grain development in rice (Oryza sativa L.). OsNCED3 encodes a chloroplast‐localized abscisic acid (ABA) biosynthetic enzyme highly expressed in the embryo of developing seeds. Disruption of OsNCED3 by CRISPR/Cas9‐mediated mutagenesis led to a lower ABA and higher gibberellic acid (GA) levels (thus a skewed ABA/GA ratio) in the embryo, promoting embryos growth and breaking seed dormancy before seed maturity and harvest, thus decreased seed dormancy and enhanced PHS in rice. However, the overexpression of OsNCED3 enhanced PHS resistance by regulating proper ABA/GA ratio in the embryo. Intriguingly, the overexpression of OsNCED3 resulted in increased grain size and weight, whereas the disruption of OsNCED3 function decreased grain size and weight. Nucleotide diversity analyses suggested that OsNCED3 may be selected during japonica populations adaptation of seed dormancy and germination. Taken together, we have identified a new OsNCED regulator involved rice PHS and grain development, and provide a potential target gene for improving PHS resistance and grain development in rice. Summary statement: Preharvest sprouting (PHS) is an unfavorable trait in cereal crops and causes serious yield loss. However, the molecular mechanism underlying PHS remains largely elusive. Here, we identified that overexpression of OsNCED3 enhanced PHS resistance by regulating proper abscisic acidgibberellic acid ratio in the embryo. In addition, the overexpression of OsNCED3 resulted in increased grain size and weight. This study provides a potential target gene for improving PHS resistance and grain development in rice. [ABSTRACT FROM AUTHOR]

Hypocotyl elongation is dramatically influenced by environmental factors and phytohormones. Indole‐3‐acetic acid (IAA) plays a prominent role in hypocotyl elongation, whereas abscisic acid (ABA) is regarded as an inhibitor through repressing IAA synthesis and signalling. However, the regulatory role of ABA in local IAA deactivation remains largely uncharacterized. In this study, we confirmed the antagonistic interplay of ABA and IAA during the hypocotyl elongation of tomato (Solanum lycopersicum) seedlings. We identified an IAA oxidase enzyme DIOXYGENASE FOR AUXIN OXIDATION2 (SlDAO2), and its expression was induced by both external and internal ABA signals in tomato hypocotyls. Moreover, the overexpression of SlDAO2 led to a reduced sensitivity to IAA, and the knockout of SlDAO2 alleviated the inhibitory effect of ABA on hypocotyl elongation. Furthermore, an ABA‐responsive regulatory SlAREB1/SlABI3‐1/SlABI5 cascade was identified to act upstream of SlDAO2 and to precisely control its expression. SlAREB1 directly bound to the ABRE present in the SlDAO2 promoter to activate SlDAO2 expression, and SlABI3‐1 enhanced while SlABI5 inhibited the activation ability of SlAREB1 by directly interacting with SlAREB1. Our findings revealed that ABA might induce local IAA oxidation and deactivation via SlDAO2 to modulate IAA homoeostasis and thereby repress hypocotyl elongation in tomato. Summary statement: We found that ABA regulates expression of IAA oxidase gene SlDAO2 via the AREB1/ABI3‐1/ABI5 transcription factor cascade, and thereby modulating IAA homeostasis and inhibiting hypocotyl elongation in tomato seedlings. [ABSTRACT FROM AUTHOR]

Precocious leaf senescence can reduce crop yield and quality by limiting the growth stage. Melatonin has been shown to delay leaf senescence; however, the underlying mechanism remains obscure. Here, we show that melatonin offsets abscisic acid (ABA) to protect photosystem II and delay the senescence of attached old leaves under the light. Melatonin induced H2O2 accumulation accompanied by an upregulation of melon respiratory burst oxidase homolog D (CmRBOHD) under ABA‐induced stress. Both melatonin and H2O2 induced the accumulation of cytoplasmic‐free Ca2+ ([Ca2+]cyt) in response to ABA, while blocking of Ca2+ influx channels attenuated melatonin‐ and H2O2‐induced ABA tolerance. CmRBOHD overexpression induced [Ca2+]cyt accumulation and delayed leaf senescence, whereas deletion of Arabidopsis AtRBOHD, a homologous gene of CmRBOHD, compromised the melatonin‐induced [Ca2+]cyt accumulation and delay of leaf senescence in Arabidopsis under ABA stress. Furthermore, melatonin, H2O2 and Ca2+ attenuated ABA‐induced K+ efflux and subsequent cell death. CmRBOHD overexpression and AtRBOHD deletion alleviated and aggravated the ABA‐induced K+ efflux, respectively. Taken together, our study unveils a new mechanism by which melatonin offsets ABA action to delay leaf senescence via RBOHD‐dependent H2O2 production that triggers [Ca2+]cyt accumulation and subsequently inhibits K+ efflux and delays cell death/leaf senescence in response to ABA. Summary statement: Melatonin has been shown to delay leaf senescence; however, the underlying mechanism remains obscure. This study shows that melatonin counteracts abscisic acid (ABA) to delay leaf senescence via RBOHD‐dependent H2O2 production that triggers cytoplasmic‐free Ca2+ accumulation and subsequently inhibits K+ efflux and delays cell death in response to ABA. [ABSTRACT FROM AUTHOR]

Although several studies have shown that AlkB homolog (ALKBH) proteins are potential RNA demethylases (referred to as 'erasers'), biological functions of only a few ALKBH proteins have been characterized to date. In this study, we determined the function of ALKBH9C (At4g36090) in seed germination and seedling growth of Arabidopsis thaliana in response to abiotic stress and abscisic acid (ABA). Seed germination of the alkbh9c mutant was delayed in response to salt, drought, cold and ABA. Moreover, seedling growth of the mutant was repressed under salt stress or ABA but enhanced under drought conditions. Notably, the stress‐responsive phenotypes were associated with the altered expression of several m6A‐modified transcripts related to salt, drought or ABA response. Global m6A levels were increased in the alkbh9c mutant, and ALKBH9C bound to m6A‐modified RNAs and had in vitro m6A demethylase activity, suggesting its potential role as an m6A eraser. The m6A levels in several stress‐responsive genes were increased in the alkbh9c mutant, and the stability of m6A‐modified transcripts was altered in the mutant. Collectively, our results suggest that m6A eraser ALKBH9C is crucial for seed germination and seedling growth of Arabidopsis in response to abiotic stresses or ABA via affecting the stability of stress‐responsive transcripts. Summary statement: Addition and removal of methylation marks in RNAs is critical for the response of plants to abiotic stresses and abscisic acid. In this study, we show that ALKBH9C is a potential m6A demethylase that plays a crucial role in seed germination and seedling growth of Arabidopsis in response to salt stress, drought stress, and abscisic acid. [ABSTRACT FROM AUTHOR]

Wheat is an essential energy and protein source for humans. Climate change brings daunting challenges to wheat yield through environmental stresses, in which phytohormones play critical roles. Nevertheless, the comprehensive understanding of wheat phytohormone responses remains elusive. Here, we investigated the transcriptome response of wheat seedlings to five phytohormones, cytokinin (6‐BA), abscisic acid (ABA), gibberellic acid (GA), jasmonate (JA) and salicylic acid (SA). We further selected two JA marker genes and cloned their promoters to drive the expression of 3XEGFP (tandem trimeric enhanced green fluorescent protein) in transgenic lines. The JA fluorescent reporter displayed a fast and stable response to JA treatment as an ideal tool to follow JA dynamics during fungal and cold stresses at a cellular resolution. Overall, this study provided a transcriptional landscape and facilitated generating fluorescent reporters to monitor the dynamics of phytohormones in food crops. Summary statement: This work described the transcriptome response of wheat seedlings to five phytohormones, 6‐BA, ABA, GA, JA, and SA. Originated from the above data, a JA fluorescent reporter actualized a fast and stable strategy tracking the cellular JA dynamics in environmental stresses, e.g., fungal pathogens or cold stress. [ABSTRACT FROM AUTHOR]

TEOSINTE BRANCHED 1/CYCLOIDEA/PCF (TCP) transcription factors play crucial roles in plant abiotic stresses. However, little is known about the role of TCP genes in the drought stress tolerance of apple. Here, we found that abscisic acid (ABA) and drought treatment reduced the expression of MdTCP46, and overexpression of MdTCP46 reduced ABA sensitivity and drought stress resistance. MdTCP46 was found to interact with MdABI5 both in vitro and in vivo, and this interaction was essential for drought resistance via the ABA‐dependent pathway. Overexpression of MdABI5 enhanced ABA sensitivity and drought stress resistance by directly activating the expression of MdEM6 and MdRD29A. MdTCP46 significantly suppressed the transcriptional activity of MdABI5, thereby negatively regulating MdABI5‐mediated ABA signalling and drought response. Overall, our results demonstrate that the MdTCP46‐MdABI5‐MdEM6/MdRD29A regulatory module plays a key role in the modulation of ABA signalling and the drought stress response. These findings provide new insight into the role of MdTCP46 in ABA signalling and abiotic stress responses. Summary statement: MdABI5 enhances abscisic acid (ABA) sensitivity and drought stress resistance by directly activating the expression of MdEM6 and MdRD29A. MdTCP46 interacts with MdABI5 and significantly suppresses the transcriptional activity of MdABI5, thereby negatively regulating MdABI5‐mediated ABA signalling and drought response. [ABSTRACT FROM AUTHOR]

Potato, a cool‐weather crop, emits volatile organic compounds (VOCs) which attract the specialist herbivore, Phthorimaea operculella, but also this herbivore's parasitic wasp, Trichogramma chilonis, an important biocontrol agent. What happens to this trophic system when heat stress challenges this agro‐ecosystem? We studied how high temperature (HT) pre‐treatments influence potato's VOC emissions and their subsequent effects on the preferences of insects, as evaluated in oviposition assays and Y‐tube olfactometers. HT pre‐stressed plants were less attractive to P. operculella adult moths, which were repelled by HT VOCs, but increased the recruitment of the parasitoid, T. chilonis, which were attracted. VOC emissions, including the most abundant constituent, ß‐caryophyllene, were enhanced by HT treatments; some constituents elicited stronger behavioural responses than others. Transcripts of many genes in the biosynthetic pathways of these VOCs were significantly enhanced by HT treatment, suggesting increases in de novo biosynthesis. HT increased the plant's stomatal apertures, and exogenous applications of the hormone, ABA, known to suppress stomatal apertures, reduced leaf volatile emissions and affected the HT‐altered plant attractions to both insects. From these results, we infer that HT stress affects this plant‐insect interaction through its influence on VOC emissions, potentially decreasing herbivore ovipositions while increasing ovipositions of the parasitoid. [ABSTRACT FROM AUTHOR]

Guard‐cell‐type aluminium‐activated malate transporters (ALMTs) are involved in stomatal closure by exporting anions from guard cells. However, their physiological and electrophysiological functions are yet to be explored. Here, we analysed the physiological and electrophysiological properties of the ALMT channels in Arabidopsis and tomato (Solanum lycopersicum). SlALMT11 was specifically expressed in tomato guard cells. External malate‐induced stomatal closure was impaired in ALMT‐suppressed lines of tomato and Arabidopsis, although abscisic acid did not influence the stomatal response in SlALMT11‐knock‐down tomato lines. Electrophysiological analyses in Xenopus oocytes showed that SlALMT11 and AtALMT12/QUAC1 exhibited characteristic bell‐shaped current‐voltage patterns dependent on extracellular malate, fumarate, and citrate. Both ALMTs could transport malate, fumarate, and succinate, but not citrate, suggesting that the guard‐cell‐type ALMTs are dicarboxylic anion channels activated by extracellular organic acids. The truncation of acidic amino acids, Asp or Glu, from the C‐terminal end of SlALMT11 or AtALMT12/QUAC1 led to the disappearance of the bell‐shaped current‐voltage patterns. Our findings establish that malate‐activated stomatal closure is mediated by guard‐cell‐type ALMT channels that require an acidic amino acid in the C‐terminus as a candidate voltage sensor in both tomato and Arabidopsis. Summary statement: Apoplastic malate induces stomatal closure mediated by ALMT‐type anion channels (SlALMT11 and AtALMT12/QUAC1) of which voltage gating requires an acidic amino acid at the C‐terminal end. [ABSTRACT FROM AUTHOR]

The FYVE domain protein required for endosomal sorting 1 (FREE1), which was previously identified as a plant‐specific component of the endosomal sorting complex required for transport machinery, plays an essential role in endosomal trafficking. Moreover, FREE1 also functions as an important negative regulator in abscisic acid (ABA) signalling. Multiple phosphorylations and ubiquitination sites have been identified in FREE1, hence unveiling the factors involved in posttranslational regulation of FREE1 is critical for comprehensively understanding FREE1‐related regulatory networks during plant growth. Here, we demonstrate that plant‐specific casein kinase I members MUT9‐like kinases 1–4 (MLKs 1–4)/Arabidopsis EL1‐like 1–4 interact with and phosphorylate FREE1 at serine residue S582, thereby modulating the nuclear accumulation of FREE1. Consequently, mutation of S582 to non‐phosphorylable residue results in reduced nuclear localization of FREE1 and enhanced ABA response. In addition, mlk123 and mlk134 triple mutants accumulate less FREE1 in the nucleus and display hypersensitive responses to ABA treatment, whereas overexpression of the nuclear‐localized FREE1 can restore the ABA sensitivity of seedling establishment in mlks triple mutants. Collectively, our study demonstrates a previously unidentified function of MLKs in attenuating ABA signalling in the nucleus by regulating the phosphorylation and nuclear accumulation of FREE1. Summary Statement: Here, we uncover a new function of plant‐specific casein kinase I members MUT9‐like kinases 1–4 in phosphorylating FYVE domain protein required for endosomal sorting 1 (FREE1) at serine residue S582, thereby modulating the nuclear accumulation of FREE1 and suppressing abscisic acid signalling in Arabidopsis thaliana. [ABSTRACT FROM AUTHOR]

Adaptation of higher plants to extreme environmental conditions is under complex regulation. Several small peptides have recently been described to modulate responses to stress conditions. The Small Paraquat resistance protein (SPQ) of Lepidium crassifolium has previously been identified due to its capacity to confer paraquat resistance to overexpressing transgenic Arabidopsis plants. Here, we show that overexpression of the closely related Arabidopsis SPQ can also enhance resistance to paraquat, while the Arabidopsis spq1 mutant is slightly hypersensitive to this herbicide. Besides being implicated in paraquat response, overexpression of SPQs enhanced sensitivity to abscisic acid (ABA), and the knockout spq1 mutant was less sensitive to ABA. Both Lepidium‐ and Arabidopsis‐derived SPQs could improve drought tolerance by reducing water loss, stabilizing photosynthetic electron transport and enhancing plant viability and survival in a water‐limited environment. Enhanced drought tolerance of SPQ‐overexpressing plants could be confirmed by characterizing various parameters of growth, morphology and photosynthesis using an automatic plant phenotyping platform with RGB and chlorophyll fluorescence imaging. Our results suggest that SPQs can be regulatory small proteins connecting ROS and ABA regulation and through that influence responses to certain stresses. Summary Statement: Small paraquat resistance proteins (SPQ) from Arabidopsis thaliana and Lepidium crassifolium enhance resistance to paraquat and improve drought tolerance when overexpressed in Arabidopsis. Abscisic acid hypersensitivity and reduced oxidative damage in a water‐limiting environment result in higher viability and survival. [ABSTRACT FROM AUTHOR]

Seed germination is a physiological process regulated by multiple factors. Abscisic acid (ABA) can inhibit seed germination to improve seedling survival under conditions of abiotic stress, and this process is often regulated by light signals. Constitutive photomorphogenic 1 (COP1) is an upstream core repressor of light signals and is involved in several ABA responses. Here, we demonstrate that COP1 is a negative regulator of the ABA‐mediated inhibition of seed germination. Disruption of COP1 enhanced Arabidopsis seed sensitivity to ABA and increased reactive oxygen species (ROS) levels. In seeds, ABA induced the translocation of COP1 to the cytoplasm, resulting in enhanced ABA‐induced ROS levels. Genetic evidence indicated that HY5 and ABI5 act downstream of COP1 in the ABA‐mediated inhibition of seed germination. ABA‐induced COP1 cytoplasmic localization increased HY5 and ABI5 protein levels in the nucleus, leading to increased expression of ABI5 target genes and ROS levels in seeds. Together, our results reveal that ABA‐induced cytoplasmic translocation of COP1 activates the HY5‐ABI5 pathway to promote the expression of ABA‐responsive genes and the accumulation of ROS during ABA‐mediated inhibition of seed germination. These findings enhance the role of COP1 in the ABA signal transduction pathway. [ABSTRACT FROM AUTHOR]

In nature, plants are frequently exposed to drought and bacterial pathogens simultaneously. However, information on how the drought and defence pathways interact and orchestrate global transcriptional regulation is limited. Here, we show that moderate drought stress enhances the susceptibility of Arabidopsis thaliana to Pseudomonas syringae pv. tomato DC3000. Using transcriptome meta‐analysis, we found that drought and bacterial stress antagonistically modulate a large set of genes predominantly involved in salicylic acid (SA) and abscisic acid (ABA) signalling networks. We identified that the levels of SA and ABA are dynamically regulated during the course of stress. Importantly, under combined stress, drought through the ABA pathway downregulates the induction of Calmodulin‐binding Protein 60 g (CBP60g) and Systemic Acquired Resistance Deficient 1 (SARD1), two transcription factors crucial for SA production upon bacterial infection. We also identified an important role of NPR1‐LIKE PROTEIN 3 and 4 (NPR3/4) transcriptional repressors in the drought‐mediated negative regulation of CBP60g/SARD1 expression. Using a genetic approach, we show that CBP60g/SARD1 expression is the key determinant of plant defence against bacterial pathogens under combined stress. Thus, these transcription factors act as critical nodes for the crosstalk between drought and bacterial stress signalling under combined stress in plants. Summary statement: Moderate drought attenuates plant defence responses against bacterial pathogens by suppressing the expression of CBP60g and SARD1, which encode two crucial transcription factors involved in activating salicylic acid machinery. [ABSTRACT FROM AUTHOR]

Increasing stomatal movement is beneficial to improve plant water use efficiency and drought resilience. Contradictory results indicate that aquaporins might regulate stomatal movement. Here, we tested whether the maize plasma membrane PIP2;5 aquaporin affects stomatal closure under water deficit, abscisic acid (ABA) or vapour pressure deficit (VPD) treatment in intact plants, detached leaves or peeled epidermis. Transpiration, stomatal conductance (gs) and aperture and reactive oxygen species (ROS) in stomatal complexes were studied in maize lines with increased or knocked down (KD) PIP2;5 gene expression. In well‐watered conditions, the PIP2;5 overexpressing (OE) plants transpired more than wild types (WTs), while no significant difference in transpiration was observed between pip2;5 KD and WT. Upon mild water deficit or low ABA concentration treatments, transpiration and gs decreased more in PIP2;5 OE lines and less in pip2;5 KD lines, in comparison with WTs. In the detached epidermis, ABA treatment induced faster stomatal closing in PIP2;5 OE lines compared to WTs, while pip2;5 KD stomata were ABA insensitive. These phenotypes were associated with guard cell ROS accumulation. Additionally, PIP2;5 is involved in the transpiration decrease observed under high VPD. These data indicate that maize PIP2;5 is a key actor increasing the sensitivity of stomatal closure to water deficit. Summary Statement: Maize PIP2;5 increases the sensitivity of stomatal closure to water deficit, abscisic acid, and high vapour potential deficit, leading to a decrease in transpiration. [ABSTRACT FROM AUTHOR]

Heat stress events are resulting in a significant negative impact on global food production. The dynamics of cellular, molecular and physiological homoeostasis in aboveground parts under heat stress are extensively deciphered. However, root responses to higher soil/air temperature or stress signalling from shoot to root are limited. Therefore, this review presents a holistic view of root physio‐morphological and molecular responses to adapt under hotter environments. Heat stress reprogrammes root cellular machinery, including crosstalk between genes, phytohormones, reactive oxygen species (ROS) and antioxidants. Spatio‐temporal regulation and long‐distance transport of phytohormones, such as auxin, cytokinin and abscisic acid (ABA) determine the root growth and development under heat stress. ABA cardinally integrates a signalling pathway involving heat shock factors, heat shock proteins and ROS to govern heat stress responses. Additionally, epigenetic modifications by transposable elements, DNA methylation and acetylation also regulate root growth under heat stress. Exogenous application of chemical compounds or biological agents such as ascorbic acid, metal ion chelators, fungi and bacteria can alleviate heat stress‐induced reduction in root biomass. Future research should focus on the systemic effect of heat stress from shoot to root with more detailed investigations to decipher the molecular cues underlying the roots architecture and function. Summary: The review focuses on the responses of the belowground root under heat stress exposure. We have summarized the various morphological, anatomical and molecular mechanisms employed by roots to mitigate the effect of heat stress, in addition to chemical and biopriming strategies. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) plays an important role in plant adaptation to water deficits, but its role in regulating root growth (primary root elongation and lateral root number) during different drought‐phases remains unclear. Here, we exposed wild‐type (WT) and ABA‐deficient (not) tomato plants to three continuous drought‐phases (moderate drying: day 0–21; severe drying: day 22–47 and re‐watering: day 48–51). It was found that WT increased primary root growth during moderate drying; maintained more lateral roots, and greater primary root and total root length under severe drying; and produced more roots after re‐watering. After RNA‐Seq analysis, we found that the auxin‐related genes in root showed different expression patterns between WT and not under drying or re‐watering. Further, exogenous supply of IAA partially recovered the root growth of ABA‐deficient not plants under three continuous drought‐phases. Our results suggested that ABA regulation of tomato root growth during soil drying and recovery can involve auxin response. Field crops regularly face period of soil‐drying and after rainfall under climate change. Our study on tomato showed that ABA/IAA interaction is involved in plant drought responses by affecting large‐scale root gene expressions and dynamically reshaping root architecture throughout the drying and re‐watering. [ABSTRACT FROM AUTHOR]

Drought stress adversely impacts crop development and yield. Maize frequently encounters drought stress during its life cycle. Improvement of drought tolerance is a priority of maize breeding programs. Here, we identified a novel transcription factor encoding gene, APETALA2 (AP2)/Ethylene response factor (ERF), which is tightly associated with drought tolerance in maize seedlings. ZmERF21 is mainly expressed in the root and leaf and it can be highly induced by polyethylene glycol treatment. Genetic analysis showed that the zmerf21 mutant plants displayed a reduced drought tolerance phenotype, accompanied by phenotypical and physiological changes that are commonly observed in drought conditions. Overexpression of ZmERF21 in maize significantly increased the chlorophyll content and activities of antioxidant enzymes under drought conditions. RNA‐Seq and DNA affinity purification sequencing analysis further revealed that ZmERF21 may directly regulate the expression of genes related to hormone (ethylene, abscisic acid) and Ca signaling as well as other stress‐response genes through binding to the promoters of potential target genes. Our results thereby provided molecular evidence of ZmERF21 is involved in the drought stress response of maize. Summary Statement: Drought stress adversely destroys maize development during the whole life cycle, finally reducing its yield and quality. Thus, improving the performance of maize against drought tolerance is a priority of breeding programs. Here, we identified a novel transcription factor ZmERF21 that is tightly associated with drought tolerance in maize seedlings. ZmERF21 is mainly expressed in root and leaf. Mechanistic analysis demonstrated that ZmERF21 could directly bind to the genes involved in hormone (ethylene, abscisic acid) and Ca signaling pathways. Furthermore, overexpression of ZmERF21 in maize significantly increased drought tolerance, evidenced by chlorophyll content and the activities of antioxidant enzymes. Taken together, our results revealed that ZmERF21 is a positive regulator in response to drought stress in maize. [ABSTRACT FROM AUTHOR]

Recent results suggest that metabolism‐mediated stomatal closure mechanisms are important to regulate differentially the stomatal speediness between ferns and angiosperms. However, evidence directly linking mesophyll metabolism and the slower stomatal conductance (gs) in ferns is missing. Here, we investigated the effect of exogenous application of abscisic acid (ABA), sucrose and mannitol on stomatal kinetics and carried out a metabolic fingerprinting analysis of ferns and angiosperms leaves harvested throughout a diel course. Fern stomata did not respond to ABA in the time period analysed. No differences in the relative decrease in gs was observed between ferns and the angiosperm following provision of sucrose or mannitol. However, ferns have slower gs responses to these compounds than angiosperms. Metabolomics analysis highlights that ferns have a higher accumulation of secondary rather than primary metabolites throughout the diel course, with the opposite being observed in angiosperms. Our results indicate that metabolism‐mediated stomatal closure mechanisms underpin the differential stomatal speediness regulation among ferns and angiosperms, in which the slower stomatal closure in ferns is associated with the lack of ABA‐responsiveness, to a reduced capacity to respond to mesophyll‐derived sucrose and to a higher carbon allocation toward secondary metabolism, which likely modulates both photosynthesis‐gs and growth‐stress tolerance trade‐offs. Summary Statement: The slower stomatal closure in ferns is associated to the lack of abscisic acid‐responsiveness, to a reduced capacity to respond to mesophyll‐derived sucrose and to a higher carbon allocation toward secondary metabolism, as compared to angiosperms. [ABSTRACT FROM AUTHOR]

Along with the ongoing climate change, drought events are predicted to become more severe. In this context, the spray‐induced gene silencing (SIGS) technique could represent a useful strategy to improve crop stress resilience. A previous study demonstrated that the Arabidopsis mutants for a glutathione S‐transferase (GST) gene had increased abscisic acid (ABA) levels and a more activated antioxidant system, both features that improved drought resilience. Here, we used SIGS to target a putative grape GST gene (VvGST40). Then, ecophysiological, biochemical and molecular responses of 'Chardonnay' cuttings were analysed during a drought and recovery time‐course. Gas exchange, ABA and t‐resveratrol concentration as well as expression of stress‐related genes were monitored in not treated controls, dsRNA‐VvGST40‐ and dsRNA‐GFP‐ (negative control of the technique) treated plants, either submitted or not to drought. VvGST40‐treated plants revealed increased resilience to severe drought as attested by the ecophysiological data. Analysis of target metabolites and antioxidant‐ and ABA‐related transcripts confirmed that VvGST40‐treated plants were in a priming status compared with controls. SIGS targeting an endogenous gene was successfully applied in grapevine, confirming the ability of this technique to be exploited not only for plant protection issues but also for functional genomic studies. Summary Statement: Here, we used the innovative SIGS technique to functionally characterize a glutathione‐S‐transferase (VvGST40) gene in grapevine which indeed showed an improved resilience when submitted to severe water stress treatment. [ABSTRACT FROM AUTHOR]

The reasons underlying the differential tolerance of Actinidia spp. to the pandemic pathogen Pseudomonas syringae pv. actinidiae (Psa) have not yet been elucidated. We hypothesized that differential plant‐defence strategies linked to transcriptome regulation, phytohormones and primary metabolism might be key and that Actinidia chinensis susceptibility results from an inefficient activation of defensive mechanisms and metabolic impairments shortly following infection. Here, 48 h postinoculation bacterial density was 10‐fold higher in A. chinensis var. deliciosa than in Actinidia arguta, accompanied by significant increases in glutamine, ornithine, jasmonic acid (JA) and salicylic acid (SA) (up to 3.2‐fold). Actinidia arguta showed decreased abscisic acid (ABA) (0.7‐fold), no changes in primary metabolites, and 20 defence‐related genes that were only differentially expressed in this species. These include GLOX1, FOX1, SN2 and RBOHA, which may contribute to its higher tolerance. Results suggest that A. chinensis' higher susceptibility to Psa is due to an inefficient activation of plant defences, with the involvement of ABA, JA and SA, leading to impairments in primary metabolism, particularly the ammonia assimilation cycle. A schematic overview on the interaction between Psa and genotypes with distinct tolerance is provided, highlighting the key transcriptomic and metabolomic aspects contributing to the different plant phenotypes after infection. Summary Statement: The pandemic bacterium P. syringae pv. actinidiae is currently the most important pathogen affecting kiwifruit productivity worldwide. Given the absence of sustainable and effective mitigation strategies, it is imperative to understand plant tolerance mechanisms that could support crop improvement and better agronomical practices. Here, we found that plant susceptibility to Psa results from an inefficient activation of plant defences, involving the jasmonic acid and salicylic acid pathways, and leads to impairments in primary metabolism, particularly the ammonia assimilation cycle. Tolerance is most likely due to a more strategic defensive and metabolic readjustment, resulting from the activation of specific defence‐related genes and to the downregulation of the abscisic acid pathway. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) transport plays a crucial role in seed germination under unfavourable conditions such as cold stress. Both heat shock protein 70 (HSP70) and voltage‐dependent anion channel (VDAC) protein are involved in cold stress responses in Arabidopsis. However, their roles in seed germination with regard to ABA signaling remain unknown. Here we demonstrated that Arabidopsis HSP70‐16 and VDAC3 jointly suppress seed germination under cold stress conditions. At 4°C, both HSP70‐16 and VDAC3 facilitated the efflux of ABA from the endosperm to the embryo and thus inhibited seed germination. HSP70‐16 interacted with VDAC3 on the plasma membrane and in the nucleus, and the interplay between HSP70‐16 and VDAC3 activated the opening of the VDAC3 ion channel. Our work established a novel function of HSP70‐16 in seed germination under cold stress and a possible association of VDAC3 activity with ABA transportation from endosperm to embryo under cold stress conditions. This study reveals that HSP70‐16 interacts with VDAC3 and facilitates the opening of the VDAC3 ion channel, which influences ABA efflux from endosperm to embryo, thus negatively regulates seed germination under cold stress. This study reveals that HSP70‐16 interacts with VDAC3 and facilitates the opening of the VDAC3 ion channel, which influences ABA efflux from endosperm to embryo, thus negatively regulates seed germination under cold stress. [ABSTRACT FROM AUTHOR]

The biosynthesis of anthocyanins has been shown to be influenced by light quality. However, the molecular mechanisms underlying the light‐mediated regulation of fruit anthocyanin biosynthesis are not well understood. In this study, we analysed the effects of supplemental red and blue light on the anthocyanin biosynthesis in non‐climacteric bilberry (Vaccinium myrtillus L.). After 6 days of continuous irradiation during ripening, both red and blue light elevated concentration of anthocyanins, up to 12‐ and 4‐folds, respectively, compared to the control. Transcriptomic analysis of ripening berries showed that both light treatments up‐regulated all the major anthocyanin structural genes, the key regulatory MYB transcription factors and abscisic acid (ABA) biosynthetic genes. However, higher induction of specific genes of anthocyanin and delphinidin biosynthesis alongside ABA signal perception and metabolism were found in red light. The difference in red and blue light signalling was found in 9‐cis‐epoxycarotenoid dioxygenase (NCED), ABA receptor pyrabactin resistance‐like (PYL) and catabolic ABA‐8'hydroxylase gene expression. Red light also up‐regulated expression of soluble N‐ethylmaleimide‐sensitive factor attachment protein receptor (SNARE) domain transporters, which may indicate involvement of these proteins in vesicular trafficking of anthocyanins during fruit ripening. Our results suggest differential signal transduction and transport mechanisms between red and blue light in ABA‐regulated anthocyanin and delphinidin biosynthesis during bilberry fruit ripening. Both red and blue light promoted anthocyanin biosynthesis in non‐climacteric bilberry fruit, regulated by abscisic acid metabolism. The key difference was detected in genes involved in abscisic acid (ABA) metabolism and signalling. Red light induced high accumulation of delphinidins towards end of berry ripening. [ABSTRACT FROM AUTHOR]

Abiotic stress, a serious threat to plants, occurs for extended periods in nature. Abscisic acid (ABA) plays a critical role in abiotic stress responses in plants. Therefore, stress responses mediated by ABA have been studied extensively, especially in short‐term responses. However, long‐term stress responses mediated by ABA remain largely unknown. To elucidate the mechanism by which plants respond to prolonged abiotic stress, we used long‐term ABA treatment that activates the signalling against abiotic stress such as dehydration and investigated mechanisms underlying the responses. Long‐term ABA treatment activates constitutive photomorphogenic 1 (COP1). Active COP1 mediates the ubiquitination of golden2‐like1 (GLK1) for degradation, contributing to lowering expression of photosynthesis‐associated genes such as glutamyl‐tRNA reductase (HEMA1) and protochlorophyllide oxidoreductase A (PORA), resulting in the suppression of chloroplast development. Moreover, COP1 activation and GLK1 degradation upon long‐term ABA treatment depend on light intensity. Additionally, plants with COP1 mutation or exposed to higher light intensity were more sensitive to salt stress. Collectively, our results demonstrate that long‐term treatment of ABA leads to activation of COP1 in a light intensity‐dependent manner for GLK1 degradation to suppress chloroplast development, which we propose to constitute a mechanism of balancing normal growth and stress responses upon the long‐term abiotic stress. Here, we show that long‐term ABA promotes GLK1 degradation through COP1 to suppress chloroplast development dependent on light intensity, revealing that balancing normal growth and stress response in long‐term stress. [ABSTRACT FROM AUTHOR]

To determine whether root‐supplied ABA alleviates saline stress, tomato (Solanum lycopersicum L. cv. Sugar Drop) was grafted onto two independent lines (NCED OE) overexpressing the SlNCED1 gene (9‐cis‐epoxycarotenoid dioxygenase) and wild type rootstocks. After 200 days of saline irrigation (EC = 3.5 dS m−1), plants with NCED OE rootstocks had 30% higher fruit yield, but decreased root biomass and lateral root development. Although NCED OE rootstocks upregulated ABA‐signalling (AREB, ATHB12), ethylene‐related (ACCs, ERFs), aquaporin (PIPs) and stress‐related (TAS14, KIN, LEA) genes, downregulation of PYL ABA receptors and signalling components (WRKYs), ethylene synthesis (ACOs) and auxin‐responsive factors occurred. Elevated SlNCED1 expression enhanced ABA levels in reproductive tissue while ABA catabolites accumulated in leaf and xylem sap suggesting homeostatic mechanisms. NCED OE also reduced xylem cytokinin transport to the shoot and stimulated foliar 2‐isopentenyl adenine (iP) accumulation and phloem transport. Moreover, increased xylem GA3 levels in growing fruit trusses were associated with enhanced reproductive growth. Improved photosynthesis without changes in stomatal conductance was consistent with reduced stress sensitivity and hormone‐mediated alteration of leaf growth and mesophyll structure. Combined with increases in leaf nutrients and flavonoids, systemic changes in hormone balance could explain enhanced vigour, reproductive growth and yield under saline stress. ABA overproducing tomato rootstocks increase shoot vigour and fruit yield under saline conditions by altering stress‐related responses, improving photosynthesis and optimizing source‐sink relationships. [ABSTRACT FROM AUTHOR]

The widespread ascomycetous fungus Diplodia pinea is a latent, necrotrophic pathogen in Pinus species causing severe damages and world‐wide economic losses. However, the interactions between pine hosts and virulent D. pinea are largely not understood. In the present study, systemic defence responses were investigated in non‐inoculated, asymptomatic needles and roots of D. pinea infected saplings of two P. sylvestris provenances under controlled greenhouse conditions. Here, we show that D. pinea infection induced a multitude of systemic responses of the phytohormone profiles and metabolic traits. Shared systemic responses of both pine provenances in needles and roots included increased abscisic acid and jasmonic acid levels. Exclusively in the roots of both provenances, enhanced salicylic acid and reduced indole‐3‐acetic acid levels, structural biomass, and elevated activities of anti‐oxidative enzymes were observed. Despite these similarities, the two pine provenances investigated different significantly in the systemic responses of both, phytohormone profiles and metabolic traits in needles and roots. However, the different systemic responses did not prevent subsequent destruction of non‐inoculated needles, but rather prevented damage to the roots. Our results provide a detailed view on systemic defence mechanisms of pine hosts that are of particular significance for the selection of provenances with improved defence capacity. Diplodia infection induced not only a multitude of systemic responses of infection‐related phytohormone profiles, but also of metabolic traits in non‐inoculated needles and roots in its pine host. [ABSTRACT FROM AUTHOR]

Through a combination of physiological, pharmacological, molecular and targeted metabolomics approaches, we showed that retention of wheat (Triticum aestivum L.) seed dormancy levels induced by low and high seed development temperatures during post‐desiccation phases is associated with modulation of gibberellin (GA) level and seed responsiveness to abscisic acid (ABA) and GA via expression of TaABI5 and TaGAMYB, respectively. Dormancy retention during imbibition, however, is associated with modulations of both ABA level and responsiveness via expression of specific ABA metabolism (TaNCED2 and TaCYP707A1) and signalling (TaPYL2, TaSnRK2, TaABI3, TaABI4 and TaABI5) genes, and alterations of GA levels and responsiveness through expression of specific GA biosynthesis (TaGA20ox1, TaGA20ox2 and TaGA3ox2) and signalling (TaGID1 and TaGID2) genes, respectively. Expression patterns of GA signalling genes, TaRHT1 and TaGAMYB, lacked positive correlation with that of GA regulated genes and dormancy level observed in seeds developed at the two temperatures, implying their regulation at post‐transcriptional level. Our results overall implicate that a shift in ABA/GA balance underlies retention of dormancy levels induced by seed development temperature during post‐desiccation and imbibition phases. Consistently, genes regulated by ABA and GA during imbibition overlapped with those differentially expressed between imbibed seeds developed at the two temperatures and mediate different biological functions. Seed development temperature influences the level of dormancy manifested in mature seeds of wheat (Triticum aestivum L.). A shift in abscisic acid/gibberellin balance underlies the retention of dormancy level induced by seed development temperatures during post‐desiccation and imbibition phases. [ABSTRACT FROM AUTHOR]

Soil drying enhances root ABA accumulation and rhizosheath formation, but whether ABA mediates rhizosheath formation is unclear. Here, we used the ABA‐deficient mutant Az34 to investigate molecular and morphological changes by which ABA could affect rhizosheath formation. Mild soil drying with intermittent watering increased rhizosheath formation by promoting root and root hair elongation. Attenuated root ABA accumulation in Az34 barley constrained the promotion of root length and root hair length by drying soil, such that Az34 had a smaller rhizosheath. Pharmacological experiments of adding fluridone (an ABA biosynthesis inhibitor) and ABA to drying soil restricted and enhanced rhizosheath formation respectively in Az34 and wild‐type Steptoe barley. RNA sequencing suggested that ABA accumulation mediates auxin synthesis and responses and root and root hair elongation in drying soil. In addition, adding indole‐3‐acetic acid (IAA) to drying soil increased rhizosheath formation by promoting root and root hair elongation in Steptoe and Az34 barley. Together, these results show that ABA accumulation induced by mild soil drying enhance barley rhizosheath formation, which may be achieved through promoting auxin response. Soil drying enhances root ABA accumulation and rhizosheath formation, but whether ABA mediates rhizosheath formation is unclear. Here, we show that ABA accumulation induced by mild soil drying enhance barley rhizosheath formation, which may be achieved through promoting auxin response. [ABSTRACT FROM AUTHOR]