Search

Under drought conditions, leaf photosynthesis is limited by the supply of CO2. Drought induces production of abscisic acid ( ABA), and ABA decreases stomatal conductance ( gs). Previous papers reported that the drought stress also causes the decrease in mesophyll conductance ( gm). However, the relationships between ABA content and gm are unclear. We investigated the responses of gm to the leaf ABA content [( ABA)L] using an ABA-deficient mutant, aba1, and the wild type ( WT) of N icotiana plumbaginifolia. We also measured leaf water potential ( ΨL) because leaf hydraulics may be related to gm. Under drought conditions, gm decreased with the increase in ( ABA)L in WT, whereas both ( ABA)L and gm were unchanged by the drought treatment in aba1. Exogenously applied ABA decreased gm in both WT and aba1 in a dose-dependent manner. ΨL in WT was decreased by the drought treatment to −0.7 MPa, whereas ΨL in aba1 was around −0.8 MPa even under the well-watered conditions and unchanged by the drought treatment. From these results, we conclude that the increase in ( ABA)L is crucial for the decrease in gm under drought conditions. We discuss possible relationships between the decrease in gm and changes in the leaf hydraulics. [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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

This article comments on:Mesophyll conductance decreases in the wild type but not in an ABA‐deficient mutant (aba1) of Nicotiana plumbaginifolia under drought conditions [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]

Drought is a cyclical phenomenon in natural environments. During dehydration, stomatal closure is mainly regulated by abscisic acid (ABA) dynamics that limit transpiration in seed plants, but following rehydration, the mechanism of gas exchange recovery is still not clear. In this study, leaf water potential (ψleaf), stomatal conductance (gs), leaf hydraulic conductance (Kleaf), foliar ABA level, ethylene emission rate in response to dehydration and rehydration were investigated in four Caragana species with isohydric (Caragana spinosa and C. pruinosa) and anisohydric (C. intermedia and C. microphylla) traits. Two isohydric species with ABA‐induced stomatal closure exhibited more sensitive gs and Kleaf to decreasing ψleaf than two anisohydric species which exhibited a switch from ABA to water potential‐driven stomatal closure during dehydration. Following rehydration, the recovery of gas exchange was not associated with a decrease in ABA level but was strongly limited by the degradation of the ethylene emission rate in all species. Furthermore, two anisohydric species with low drought‐induced ethylene production exhibited more rapid recovery in gas exchange upon rehydration. Our results indicated that ethylene is a key factor regulating the drought‐recovery ability in terms of gas exchange, which may shape species adaptation to drought and potential species distribution. Drought is a cyclical phenomenon in natural environments. During dehydration, stomatal closure is mainly regulated by abscisic acid (ABA) dynamics that limit transpiration in seed plants, but the mechanisms of gas exchange recovery are still not clear following rehydration. The results in this study indicate that ethylene is a key factor regulating the drought‐recovery ability in terms of gas exchange, which may shape species adaptation to drought and potential species distribution. [ABSTRACT FROM AUTHOR]

Protein degradation by the ubiquitin/26S proteasome system is a critical process that modulates many eukaryotic cellular processes. E3 ligase usually modulates stress response by adjusting the stability of transcription factors. Previous studies have shown that a RING‐type E3 ligase, CaASRF1, positively modulates abscisic acid (ABA) signalling and ABA‐mediated drought response by modulating the stability of CaAIBZ1 and CaATBZ1. In this study, we conducted yeast two‐hybrid (Y2H) screening with CaATBZ1 to isolate an additional modulator, identified as CaATIR1 (Capsicum annuumATBZ1 Interacting RING finger protein 1). CaATIR1 has E3 ligase activity and promoted CaATBZ1 degradation using the 26S proteasome system. We investigated the loss‐of and gain‐of functions of this E3 ligase by using silencing pepper and overexpressing (OX) Arabidopsis plants, respectively. In response to ABA and drought treatments, CaATIR1‐silenced pepper plants showed ABA insensitive and drought‐sensitive phenotypes, while CaATIR1‐OX plants showed the opposite phenotypes. Additionally, CaATBZ1‐silencing rescued the ABA insensitive and drought‐sensitive phenotypes of CaATIR1‐silencing pepper plants. Taken together, these data demonstrate that the stability of CaATBZ1 mediated by CaATIR1 has a crucial role in drought stress signalling in pepper plants. In our previous studies, we elucidated that RING‐type E3 ligase CaASRF1 positively modulates ABA signalling and drought response via adjusting the stability of CaAIBZ1 and CaATBZ1. Here, we identified another E3 ligase, CaATIR1, which interacts with and ubiquitinates CaATBZ1. CaATIR1 acts as positive modulator in drought response via ABA‐mediated signalling. [ABSTRACT FROM AUTHOR]

This article comments on: A novel strigolactone‐miR156 module controls stomatal behaviour during drought recovery [ABSTRACT FROM AUTHOR]

Climate change threatens food security, and plant science researchers have investigated methods of sustaining crop yield under drought. One approach has been to overproduce abscisic acid (ABA) to enhance water use efficiency. However, the concomitant effects of ABA overproduction on plant vascular system functioning are critical as it influences vulnerability to xylem hydraulic failure. We investigated these effects by comparing physiological and hydraulic responses to water deficit between a tomato (Solanum lycopersicum) wild type control (WT) and a transgenic line overproducing ABA (sp12). Under well‐watered conditions, the sp12 line displayed similar growth rate and greater water use efficiency by operating at lower maximum stomatal conductance. X‐ray microtomography revealed that sp12 was significantly more vulnerable to xylem embolism, resulting in a reduced hydraulic safety margin. We also observed a significant ontogenic effect on vulnerability to xylem embolism for both WT and sp12. This study demonstrates that the greater water use efficiency in the tomato ABA overproducing line is associated with higher vulnerability of the vascular system to embolism and a higher risk of hydraulic failure. Integrating hydraulic traits into breeding programmes represents a critical step for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under water deficit. We show that an ABA overproducing tomato line exhibits greater water use efficiency than its wild type counterpart but higher vulnerability to hydraulic failure through increased vulnerability to xylem embolism and a reduced hydraulic safety margin. This suggests that breeding programmes should integrate hydraulic traits for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under drought. [ABSTRACT FROM AUTHOR]

Aquaporins influence water flow in plants, yet little is known of their involvement in the water‐driven process of seed germination. We therefore investigated their role in seeds in the laboratory and under field and global warming conditions. We mapped the expression of tonoplast intrinsic proteins (TIPs) during dormancy cycling and during germination under normal and water stress conditions. We found that the two key tonoplast aquaporins, TIP3;1 and TIP3;2, which have previously been implicated in water or solute transport, respectively, act antagonistically to modulate the response to abscisic acid, with TIP3;1 being a positive and TIP3;2 a negative regulator. A third isoform, TIP4;1, which is normally expressed upon completion of germination, was found to play an earlier role during water stress. Seed TIPs also contribute to the regulation of depth of primary dormancy and differences in the induction of secondary dormancy during dormancy cycling. Protein and gene expression during annual cycling under field conditions and a global warming scenario further illustrate this role. We propose that the different responses of the seed TIP contribute to mechanisms that influence dormancy status and the timing of germination under variable soil conditions. Aquaporins influence water flow in plants, yet little is known of their involvement in the water‐driven process of seed germination. We therefore investigated their role in seeds, both in the laboratory and field. We mapped the expression of tonoplast intrinsic proteins during germination in normal and water stress conditions. We found that the two key tonoplast aquaporins, TIP3;1 and TIP3;2, act antagonistically to modulate the response to ABA, with TIP3;1 being a positive and TIP3;2 a negative regulator. A third isoform, TIP4;1, which is normally expressed upon completion of germination, was found to play an earlier role during water stress. Seed TIPs also regulate the depth of primary dormancy and differences in the induction of secondary dormancy in a similar manner. We propose that the different responses of the seed TIP constitute a mechanism to influence germination under water stress and dormancy cycling in variable soil conditions. [ABSTRACT FROM AUTHOR]

C3 photosynthesis is often limited by CO2 diffusivity or stomatal (gs) and mesophyll (gm) conductances. To characterize effects of stomatal closure induced by either high CO2 or abscisic acid (ABA) application on gm, we examined gs and gm in the wild type (Col‐0) and ost1 and slac1‐2 mutants of Arabidopsis thaliana grown at 390 or 780 μmol mol−1 CO2. Stomata of these mutants were reported to be insensitive to both high CO2 and ABA. When the ambient CO2 increased instantaneously, gm decreased in all these plants, whereas gs in ost1 and slac1‐2 was unchanged. Therefore, the decrease in gm in response to high CO2 occurred irrespective of the responses of gs. gm was mainly determined by the instantaneous CO2 concentration during the measurement and not markedly by the CO2 concentration during the growth. Exogenous application of ABA to Col‐0 caused the decrease in the intercellular CO2 concentration (Ci). With the decrease in Ci, gm did not increase but decreased, indicating that the response of gm to CO2 and that to ABA are differently regulated and that ABA content in the leaves plays an important role in the regulation of gm. This study aimed at investigating the responses of gm to instantaneous and growth CO2 levels and ABA. To avoid the possible effect of gs on gm, we used the Arabidopsis thaliana mutants lacking stomatal responses to elevated CO2 and ABA, ost1 and slac1‐2. Photosynthetic characteristics of these mutants and the wild type were compared. These experiments provided the clear evidence that gm responds differently to CO2 and ABA, although both elevated CO2 and ABA decreased gm. Further, we showed that the decrease in gm in response to elevated CO2 was not a transient phenomenon and was hardly restored by even a long‐term cultivation at elevated CO2. [ABSTRACT FROM AUTHOR]

High temperature at grain filling can severely reduce wheat yield. Heat shock factors ( Hsfs) are central regulators in heat acclimation. This study investigated the role of TaHsfC2a, a member of the monocot-specific HsfC2 subclass, in the regulation of heat protection genes in Triticum aestivum. Three TaHsfC2a homoeologous genes were highly expressed in wheat grains during grain filling and showed only transient up-regulation in the leaves by heat stress but were markedly up-regulated by drought and abscisic acid (ABA) treatment. Overexpression of TaHsfC2a-B in transgenic wheat resulted in up-regulation of a suite of heat protection genes (e.g. TaHSP70d and TaGalSyn). Most TaHsfC2a-B target genes were heat, drought and ABA inducible. Transactivation analysis of two representative targets ( TaHSP70d and TaGalSyn) showed that TaHsfC2a-B activated expression of reporters driven by these target promoters. Promoter mutagenesis analyses revealed that heat shock element is responsible for transactivation by TaHsfC2a-B and heat/drought induction. TaHsfC2a-B-overexpressing wheat showed improved thermotolerance but not dehydration tolerance. Most TaHsfC2a-B target genes were co-up-regulated in developing grains with TaHsfC2a genes. These data suggest that TaHsfC2a-B is a transcriptional activator of heat protection genes and serves as a proactive mechanism for heat protection in developing wheat grains via the ABA-mediated regulatory pathway. [ABSTRACT FROM AUTHOR]

The large WRKY transcription factor family is mainly involved in regulating plant immune responses. Arabidopsis WRKY33 is a key transcriptional regulator of hormonal and metabolic processes towards Botrytis cinerea strain 2100 infection and is essential for resistance. In contrast to B. cinerea strain 2100, the strain B05.10 is virulent on wild-type (WT) Col-0 Arabidopsis plants highlighting the genetic diversity within this pathogen species. We analysed how early WRKY33-dependent responses are affected upon infection with strain B05.10 and found that most of these responses were strongly dampened during this interaction. Ectopic expression of WRKY33 resulted in complete resistance towards this strain indicating that virulence of B05.10, at least partly, depends on suppressing WRKY33 expression/protein accumulation. As a consequence, the expression levels of direct WRKY33 target genes, including those involved in the biosynthesis of camalexin, were also reduced upon infection. Concomitantly, elevated levels of the phytohormone abscisic acid (ABA) were observed. Molecular and genetic studies revealed that ABA negatively influences defence to B05.10 and effects jasmonic acid/ethylene (JA/ET) and salicylic acid (SA) levels. Susceptibility/resistance was determined by the antagonistic effect of ABA on JA, and this crosstalk required suppressing WRKY33 functions at early infection stages. This indicates that B. cinerea B05.10 promotes disease by suppressing WRKY33-mediated host defences. [ABSTRACT FROM AUTHOR]

Seeds serve as a great model to study plant responses to drought stress, which is largely mediated by abscisic acid (ABA). The ABA responsive element (ABRE) is a key cis-regulatory element in ABA signalling. However, its consensus sequence (ACGTG(G/T)C) is present in the promoters of only about 40% of ABA-induced genes in rice aleurone cells, suggesting other ABREs may exist. To identify novel ABREs, RNA sequencing was performed on aleurone cells of rice seeds treated with 20 μM ABA. Gibbs sampling was used to identify enriched elements, and particle bombardment-mediated transient expression studies were performed to verify the function. Gene ontology analysis was performed to predict the roles of genes containing the novel ABREs. This study revealed 2443 ABA-inducible genes and a novel ABRE, designated as ABREN, which was experimentally verified to mediate ABA signalling in rice aleurone cells. Many of the ABREN-containing genes are predicted to be involved in stress responses and transcription. Analysis of other species suggests that the ABREN may be monocot specific. This study also revealed interesting expression patterns of genes involved in ABA metabolism and signalling. Collectively, this study advanced our understanding of diverse cis-regulatory sequences and the transcriptomes underlying ABA responses in rice aleurone cells. [ABSTRACT FROM AUTHOR]

Plants dynamically regulate water use by the movement of stomata on the surface of leaves. Stomatal responses to changes in vapour pressure deficit (VPD) are the principal regulator of daytime transpiration and water use efficiency in land plants. In angiosperms, stomatal responses to VPD appear to be regulated by the phytohormone abscisic acid (ABA), yet the origin of this ABA is controversial. After a 20 min exposure of plants, from three diverse angiosperm species, to a doubling in VPD, stomata closed, foliar ABA levels increased and the expression of the gene encoding the key, rate-limiting carotenoid cleavage enzyme (9- cis-epoxycarotenoid dioxygenase, NCED) in the ABA biosynthetic pathway was significantly up-regulated. The NCED gene was the only gene in the ABA biosynthetic pathway to be up-regulated over the short time scale corresponding to the response of stomata. The closure of stomata and rapid increase in foliar ABA levels could not be explained by the release of ABA from internal stores in the leaf or the hydrolysis of the conjugate ABA-glucose ester. These results implicate an extremely rapid de novo biosynthesis of ABA, mediated by a single gene, as the means by which angiosperm stomata respond to natural changes in VPD. [ABSTRACT FROM AUTHOR]

Phytohormones are central players in sensing and signalling numerous environmental conditions like drought. In this work, hormone profiling together with gene expression of key enzymes involved in abscisic acid ( ABA) and jasmonate biosynthesis were studied in desiccating Arabidopsis roots. Jasmonic acid ( JA) content transiently increased after stress imposition whereas progressive and concomitant ABA and Jasmonoyl Isoleucine ( JA- Ile) accumulations were detected. Molecular data suggest that, at least, part of the hormonal regulation takes place at the biosynthetic level. These observations also point to a possible involvement of jasmonates on ABA biosynthesis under stress. To test this hypothesis, mutants impaired in jasmonate biosynthesis ( opr3, lox6 and jar1-1) and in JA-dependent signalling ( coi1) were employed. Results showed that the early JA accumulation leading to JA-Ile build up was necessary for an ABA increase in roots under two different water stress conditions. Signal transduction between water stress-induced JA-Ile accumulation and COI1 is necessary for a full induction of the ABA biosynthesis pathway and subsequent hormone accumulation in roots of Arabidopsis plants. The present work adds a level of interaction between jasmonates and ABA at the biosynthetic level. [ABSTRACT FROM AUTHOR]

The plant hormone abscisic acid ( ABA) is a primary regulator of plant transpiration, but its influence in determining seasonal stomatal behaviour in natural plant communities is poorly understood. We examined distantly related vascular plants growing together in a seasonally dry, monsoonal environment to determine whether ABA dynamics contributed to contrasting water use patterns in this natural setting. Regular sampling of angiosperm, cycad, conifer and fern species revealed characteristic seasonal patterns in ABA production, but these were highly distinct among species. Although no general relationship was observed between ABA levels, plant hydration or stomatal conductance among species, the seasonal dynamics in stomatal behaviour within species were predictable functions of either ABA or leaf water potential. Strong divergence in the seasonal role of ABA among species suggests that modification in ABA-stomatal interactions represents an important evolutionary pathway for adaptation in plant water use. [ABSTRACT FROM AUTHOR]

Sunflower ( H elianthus annuus L.) seed dormancy is regulated by reactive oxygen species ( ROS) and can be alleviated by incubating dormant embryos in the presence of methylviologen ( MV), a ROS-generating compound. Ethylene alleviates sunflower seed dormancy whereas abscisic acid ( ABA) represses germination. The purposes of this study were to identify the molecular basis of ROS effect on seed germination and to investigate their possible relationship with hormone signalling pathways. Ethylene treatment provoked ROS generation in embryonic axis whereas ABA had no effect on their production. The beneficial effect of ethylene on germination was lowered in the presence of antioxidant compounds, and MV suppressed the inhibitory effect of ABA. MV treatment did not alter significantly ethylene nor ABA production during seed imbibition. Microarray analysis showed that MV treatment triggered differential expression of 120 probe sets (59 more abundant and 61 less abundant genes), and most of the identified transcripts were related to cell signalling components. Many transcripts less represented in MV-treated seeds were involved in ABA signalling, thus suggesting an interaction between ROS and ABA signalling pathways at the transcriptional level. Altogether, these results shed new light on the crosstalk between ROS and plant hormones in seed germination. [ABSTRACT FROM AUTHOR]