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Global agricultural demand and the impact of fluctuating climatic conditions including global warming have catastrophically limited crop productivity and immensely outstretched the market value of agricultural products leading to acute inflation. The effect of desiccation or drought stress in plants is manifested at three levels viz. morphological, biochemical, and molecular and plants possess their own molecular and signaling arsenal to combat or ameliorate various stresses. For decades, stress-tolerant cultivars have been investigated and modulation of polyamine (PA) signaling was found to play a major role in attenuating environmental stresses including drought as major abiotic stress. PA metabolism pathways with their ability to crosstalk with both primary and secondary metabolic pathways have been correlated with several other responses such as seed germination, plant growth, development, defense, hormonal regulation, stress tolerance, and crop yield. Recent transcriptomic and metabolomic approaches have expanded the knowledge on the regulation of stress-induced biochemical, molecular, and physiological alterations. To fully comprehend the intricate biochemical network of plant stress physiology, it is necessary to identify exact responses against specific stress stimuli, interpret concurrent epigenetic alterations, and use molecular switching. The present review encompasses recent updates on drought tolerance mechanisms mediated by diverse polyamines playing significant roles in metabolic regulation, oxidative stress management, and systematic stress-reversal signaling. Besides, the drought stress-reversal role of polyamines and their cross-talks with other signaling molecules have also been documented. Gene, enzyme, and transcription factor (TF) functional features were retrieved from the published papers involving transgenic or mutant plants with over-expression or loss-of-function investigations. [ABSTRACT FROM AUTHOR]

One of the favorite issues for the ecologists and physiologists is searching the effects of the environmental factors (i.e. salinity, temperature, drought, rainfall, etc.) in the plants. In the present paper, the response of the enzymatic and non-enzymatic antioxidants in different populations of Pistacia atlantica and Pistacia khinjuk were investigated under different climatic conditions. Ten trees of any population of P. atlantica and P. khinjuk were garnered from diverse locations of Iran in September, 2017. The leaf samples were transferred to the laboratory using liquid nitrogen and were frozen for analysis of enzymatic and non-enzymatic antioxidants in different populations. According to the soil and climatic analyses, Jebalbarez, Sangan and Anjirk are more stressful compared to other regions. Generally, our results unveiled that the contents of protein, proline and total soluble sugar like compatible osmolytes in some populations of P. atlantica are higher than those of P. khinjuk. The antioxidant enzyme activities including superoxide dismutase, peroxidase and polyphenol oxidase were more in P. khinjuk. The activity of key enzymes in the biosynthesis pathway of the phenolic compounds in P. khinjuk was more than that of P. atlantica. Furthermore, the content of non-enzymatic antioxidants such as phenol, flavonoids and tocopherols in P. atlantica was higher than that of P. khinjuk. The respiratory enzymes (e.g. aconitase, fumarase and succinate dehydrogenase) had high activity in P. khinjuk. P. atlantica used more non-enzymatic systems; however, P. khinjuk applied the enzymatic system in response to different climatic conditions. In conclusion, the present study revealed that P. atlantica used more of the osmoregulation and non-enzymatic system; however, P. khinjuk utilized the enzymatic antioxidant system and the respiratory enzymes in response to the ecophysiological conditions. [ABSTRACT FROM AUTHOR]

Background: The drought condition is responsible for considerable losses in soybean production, which in turn may result in billionaire losses. After drought perception, plants activate a cascade of protecting genes against water deficit (WD), many of which are responsive to abscisic acid, the most important phytohormone to plants' adaptation. This work aimed to recover abscisic acid (ABA)-responsive differentially expressed genes (DEG) from an RNA-Seq, carried out from leaves and roots of drought-sensitive (BR16) and tolerant (Embrapa 48) soybean cultivars under mild (MiWD), moderate (MoWD), and severe (SWD) water-deficit treatments. Enriched ABA-responsive pathways important to drought tolerance in soybean were also identified. Results: In drought-sensitive and tolerant soybean cultivars, approximately 75% of genes were identified as ABA-responsive by containing more than two ABRE (ABA-responsive elements) in the promoter region. Most of these genes were positively regulated. Roots were the tissue with more ABA-responsive genes and pathways triggered in response to WD in both cultivars, although, on the tolerant cultivar, these pathways were higher expressed. The most important enriched ABA pathways observed in the roots of both cultivars were involved in sugar and sulfur amino acid biosynthesis, osmoregulation, and crosstalk among ABA and ethylene, jasmonate, auxin, and cytokinin. Other pathways enriched were involved in phytoalexin production, ROS homeostasis, and membrane stability by glycerolipid and glycerophospholipid production. ABA-responsive genes were also ordered based on their expression profile in tissue and cultivar, and nine confidence groups could be observed. More than 80% of these clustered genes showed the same regulation profile under MiWd, MoWD, and SWD treatments. Activation of ABA biosynthesis under water deficit was validated by RT-qPCR by increasing the expression level of NCED3, an important enzyme in this pathway, and GOLS, a known ABA-responsive gene. Conclusions: A robust catalog of ABA-responsive genes was made available in this work. Considering ABA's role in drought-response mechanisms, the genes in the groups pointed out in this study would be reliable candidates to be used in strategies to develop soybean lines more tolerant to drought. This paper, presented for the first time, ABA-responsive genes and ABA-enriched pathways in contrasting soybean cultivars for drought tolerance. [ABSTRACT FROM AUTHOR]

Rice sulfite reductase (OsSiR) is important protein in reducing sulfite to sulfide. In this paper, it is aimed to shed light on OsSiR's probable structure, function, and expression using in silico methods and test its responses under drought and salt stresses. Moreover, it was also analyzed if OsSiR was structurally different from other SiR proteins. We estimated that OsSiR lacks ribbon–helix–helix DNA-binding motif allowing it to bind to DNA; therefore, it was probably localized in stroma as a non-nucleoid-type protein. Also, we found that OsSiR expression was regulated by JA in roots and by crosstalk of JA and ABA in shoots. RT-qPCR results showed that there was 20% increase in the expression of OsSiR at 3rd h of the salt treatment. However, OsSiR was downregulated when exposed to drought stress and salt stress for longer periods of time, respectively. OsSiR has a high post-translational potential because of its high phosphorylation sites. This may be originating from the most prevalent residue, Gly, facilitating its binding to phosphates in OsSiR. Our docking results showed that ligand binding residues of OsSiR (Arg159, Thr162, Gln167, and Pro501) were also active site residues of OsSiR. Both two domains of OsSiR interacted with sulfite and the number of the residues in 4Fe–4S domain (PF01077) was higher. The findings in this study are important in terms of structural and expressional studies of rice SiR (OsSiR) and can be used for SiR proteins in sorghum (Sorghum bicolor), maize (Zea mays), and foxtail millet (Setaria italica), which are closely related and highly similar to OsSiR in terms of sequence and predicted 3D structure. [ABSTRACT FROM AUTHOR]

In the course of evolution, plants have developed numerous specific regulatory signal pathways, which are hormonal for the most part. Phytohormones comprise not only such generally recognized endogenous growth regulators as abscisic acid, auxins, cytokinins, gibberellins, brassinosteroids (BS), ethylene, salicylic acid (SA), and jasmonates but also recently described derivatives of apocarotenoids—strigolactones (SL). Signal pathways interact at the level of biosynthesis of messengers and their translocation as well as upon activation of target genes. Since abiotic and biotic environmental stressors negatively influence plant productivity, understanding of molecular mechanisms of regulation induced by stress agents may help researchers to produce stress-resistant and high-yielding plants using molecular techniques. This paper is a review of present-day literature dealing with the interaction and interference of nonhormonal and hormonal signals regulating growth and development of plants under ever-changing environmental conditions. [ABSTRACT FROM AUTHOR]

Background and aims: Plant parasitic nematodes (PPNs) are among the most important pests in agriculture. Chemical inputs are widely used for their control; however, the negative impact of these agrochemicals on environmental and human health is a current concern. Biological control and interventions on rhizosphere signaling are promising ecofriendly alternatives for managing these pests in the field. Nevertheless, the molecular mechanisms involved in plant-PPN interaction need to be unraveled in order to develop appropriate management strategies. Strigolactones (SLs) are phytohormones that are exuded from roots, acting as signaling molecules in the rhizosphere. They are important cues in the establishment of arbuscular mycorrhizal and Rhizobium-legume symbioses. Recently, it has been shown that SLs can also affect the interaction between plants and certain PPN species; however, data are scarce and ambiguous. Some studies propose that SLs positively regulate PPN species performance acting as attractants to roots, or by inhibiting plant defense responses. On the contrary, other studies suggest that SLs could negatively regulate PPN performance by reducing abscisic acid, or by promoting plant interactions with beneficial soil microorganisms. In the present Opinion paper, we discuss these controversial results and propose future research challenges to develop new management strategies against these harmful PPN species. [ABSTRACT FROM AUTHOR]

Plant mortality is a complex process influenced by both biotic and abiotic factors. In recent decades, widespread mortality events have been attributed to increasing drought severity, which has motivated research to examine the physiological mechanisms of drought-induced mortality, particularly hydraulic failure. Drought-based mortality mechanisms are further influenced by plant interactions with biota such as neighboring plants, insect pests, and microbes. In this review, we highlight some of the most influential papers addressing these biotic interactions and their influence on plant mortality. Plant–plant interactions can be positive (facilitation), neutral, or negative (competition), depending on drought intensity and neighbor identity. For example, stand-scale mortality likely increases with basal area (an index of competition). However, the diversity of forest stands matters, as more diverse forests suffer less mortality from drought than species-poor forests. Dense forest stands also increase bark beetle attack frequency, which can exacerbate drought stress and mortality, particularly for fast-growing species with lower defense allocation. In some cases, however, drought stress can alleviate biotic attack, depending on feedbacks between plant and pest physiology. Finally, plant interactions with beneficial microorganisms can increase drought tolerance, reduce the likelihood of mortality, and even extend plant distributions into drier habitats. Our review suggests more work is needed in natural herbaceous plant communities as well as dry tropical ecosystems where mortality mechanisms are less understood. Overall, relatively few studies directly link biotic interactions with the physiological mechanisms of mortality. Simultaneous manipulations of biotic interactions and measurements of physiological thresholds (e.g., xylem cavitation) are needed to fully represent biotic interactions in predictive models of plant mortality. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its occurrence may cause the shorten leaf photosynthetic period and markedly lowered grain yield. However, the physiological metabolism underlying N deficiency-induced leaf senescence and its relationship with the abscisic acid (ABA) concentration and reactive oxygen species (ROS) burst in leaf tissues are not well understood. In this paper, the effect of N supply on several senescence-related physiological parameters and its relation to the temporal patterns of ABA concentration and ROS accumulation during leaf senescence were investigated using the premature senescence of flag leaf mutant rice (psf) and its wild type under three N treatments. The results showed that N deficiency hastened the initiation and progression of leaf senescence, and this occurrence was closely associated with the upregulated expression of 9-cis-epoxycarotenoiddioxygenase genes (NCEDs) and with the downregulated expression of two ABA 8′-hydroxylase isoform genes (ABA8ox2 and ABA8ox3) under LN treatment. Contrarily, HN supply delayed the initiation and progression of leaf senescence, concurrently with the suppressed ABA biosynthesis and relatively lower level of ABA concentration in leaf tissues. Exogenous ABA incubation enhanced ROS generation and MDA accumulation in a dose-dependent manner, but it decreased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in detached leaf. These results suggested that the participation of ABA in the regulation of ROS generation and N assimilating/remobilizing metabolism in rice leaves was strongly responsible for induction of leaf senescence by N deficiency. [ABSTRACT FROM AUTHOR]

Shaggy-related protein kinase (SK) plays important roles in the plant growth development, signal transduction, abiotic stress and biotic stress and substance metabolism regulation. In the present paper, a cDNA sequence encoding MmSK (GenBank accession No: KY348867) was cloned from the leaves of mulberry based on mulberry expressed sequence tags (EST) and homologous cloning technology using RT-PCR, which was 1705 bp in length with a full open reading frame (ORF) of 1236 bp encoding a protein of 411 amino acids. The estimated molecular weight and isoelectric point (pI) of the putative protein were 46.55 kDa and 8.61, respectively. Conservation domain structure analysis indicated that MmSK protein had typical structure of the protein kinase domain and belonged to GSK3/shaggy protein kinase family. Multiple sequence alignment and phylogenetic analysis showed that the homology between the amino acid sequences encoded by the MmSK gene and various species was more than 89%. Quantitative real-time PCR (qRT-PCR) analysis revealed that MmSK was expressed in all the tested tissues including leaf, bud, fruit, stem, phloem and xylem of the mulberry with the highest expression in the phloem. The expression level of the mRNA has changed significantly under salt, drought, cold and ABA stress treatments compared to the normal growth environment. Overall, these results showed a better understanding of the molecular basis for the signal transduction mechanism during the stress responses in mulberry trees. [ABSTRACT FROM AUTHOR]

Key message: The spatial and temporal distributions of plant hormones during tree-ring formation are beginning to be elucidated. Plant hormones play specific roles in tree-ring formation depending on the developmental zone in which they operate. Tree rings are the result of the seasonal activity of the vascular cambium, the secondary meristem of woody angiosperms and gymnosperms. During tree-ring formation, a combination of endogenous and environmental factors affects cambial division, cell differentiation and maturation; this, in turn, affects wood quantity and quality. Among the endogenous factors affecting tree-ring formation, plant hormones are recognized as determinant players in regulating many aspects of the features and fate of each xylem cell. Most of our knowledge regarding the roles of plant hormones on tree-ring formation comes from herbaceous plants, although an increasing interest involves the analysis of the hormonal patterns in tree-species. This paper reviews the state of knowledge of the role of plant hormones during tree-ring formation by focusing on experiments performed on woody species. An overview of the main plant hormones and their main activities during radial tree growth will be followed by discussion of their role in each tree-ring developmental stage and in the overall tree-ring seasonal pattern. [ABSTRACT FROM AUTHOR]

Gibberellins (GAs), as one of the important hormones in regulating the growth and development of higher plants, can significantly promote cell elongation and expansion. Celery is a widely grown leafy vegetable crop with rich nutritional value. However, the effect of gibberellins on celery leaves is unclear. In this paper, the celery variety "Jinnan Shiqin" plants were treated with gibberellic acid (GA3) and paclobutrazol (PBZ, a gibberellin inhibitor). Our results showed that GA3 treatment promoted the growth of celery leaves and caused lignification of celery leaf tissue. In addition, the transcript levels of genes associated with gibberellins, auxin, cytokinins, ethylene, jasmonic acid, abscisic acid, and brassinolide were altered in response to increased or decreased exogenous gibberellins or inhibitor. GA3 may regulate celery growth by interacting with other hormones through crosstalk mechanisms. This study provided a reference for further study of the regulation mechanism of gibberellins metabolism, and exerted effects on understanding the role of gibberellins in the growth and development of celery. [ABSTRACT FROM AUTHOR]

Parallel to the discovery of auxin as a growth-promoting hormone in the first half of the last century, it became evident that inhibitors of auxin-induced cell elongation, seed germination and bud growth also existed in plants. Their activity was noticed first in more or less unspecific bioassays, and their natural function remained unknown for a long time. The introduction of paper chromatography in combination with bioassays enabled improved separation of plant extracts and identification of biologically active compounds. By means of these new techniques, a highly active growth inhibitory fraction named 'inhibitor β' was discovered in many plants. Evidence that this fraction seemed also to be involved in abscission processes resulted in the name 'abscisin II', whereas another research group that investigated the possible role of inhibitor β in bud dormancy proposed the name 'dormin'. Great efforts were made to identify the chemical nature of the two compounds. In 1965, it was recognized that abscisin II and dormin possessed the same chemical structure, which received the name 'abscisic acid' (ABA). Soon afterwards the extraordinary role of ABA as a hormone involved in stress reactions and in seed maturation was discovered, whereas its suggested function in abscission and bud dormancy processes has not been well established until now. The name ABA is therefore not adequate with regard to the hormonal functions, but it is acceptable with regard to priority rules. [ABSTRACT FROM AUTHOR]

The coordination between kinases and phosphatases is crucial for regulating the phosphorylation levels of essential signaling molecules. Methods enabling precise control of kinase activities are valuable for understanding the kinase functions and for developing targeted therapies. Here, we use the abscisic acid (ABA)-induced proximity system to reversibly control kinase signaling by recruiting phosphatases. Using this method, we found that the oncogenic tyrosine kinase BCR::ABL1 can be inhibited by recruiting various cytoplasmic phosphatases. We also discovered that the oncogenic serine/threonine kinase BRAF(V600E), which has been reported to bypass phosphorylation regulation, can be positively regulated by protein phosphatase 1 (PP1) and negatively regulated by PP5. Additionally, we observed that the dual-specificity kinase MEK1 can be inhibited by recruiting PP5. This suggests that bifunctional molecules capable of recruiting PP5 to MEK or RAF kinases could be promising anticancer drug candidates. Thus, the ABA-induced dephosphorylation method enables rapid screening of phosphatases to precisely control kinase signaling. The abscisic acid (ABA)-induced proximity system enables reversible control of kinase signaling by recruiting phosphatases, with potential therapeutic implications for targeting BCR::ABL1 and drug-resistant BRAF(V600E) variants. [ABSTRACT FROM AUTHOR]

Unfavourable conditions, such as prolonged drought and high salinity, pose a threat to the survival and agricultural yield of plants. The phytohormone ABA plays a key role in the regulation of plant stress adaptation and is often maintained at high levels for extended periods. While much is known about ABA signal perception and activation in the early signalling stage, the molecular mechanism underlying desensitization of ABA signalling remains largely unknown. Here we demonstrate that in the endoplasmic reticulum (ER)-Golgi network, the key regulators of ABA signalling, SnRK2.2/2.3, undergo N-glycosylation, which promotes their redistribution from the nucleus to the peroxisomes in Arabidopsis roots and influences the transcriptional response in the nucleus during prolonged ABA signalling. On the peroxisomal membrane, SnRK2s can interact with glucose-6-phosphate (G6P)/phosphate translocator 1 (GPT1) to maintain NADPH homeostasis through increased activity of the peroxisomal oxidative pentose phosphate pathway (OPPP). The resulting maintenance of NADPH is essential for the modulation of hydrogen peroxide (H2O2) accumulation, thereby relieving ABA-induced root growth inhibition. The subcellular dynamics of SnRK2s, mediated by N-glycosylation suggest that ABA responses transition from transcriptional regulation in the nucleus to metabolic processes in the peroxisomes, aiding plants in adapting to long-term environmental stress. During prolonged ABA signalling, N-glycosylation-mediated nucleus-peroxisome subcellular dynamics of SnRK2s orchestrate a transition state from short-term sensitive response to long-term acclimation to environmental stress. [ABSTRACT FROM AUTHOR]

Background: We aimed to gain insight into the response mechanism of alfalfa (Medicago sativa) to drought stress by recognizing and analyzing drought-responsive genes in the roots of different root types of alfalfa. The rhizomatous-rooted M. sativa cv.'Qingshui' (QS), tap-rooted M. sativa cv.'Longdong' (LD), and creeping-rooted M. varia cv. 'Gongnong No. 4' (GN) were used to analyze the transcriptome information and physiological characteristics of the root systems of the cultivars under simulated drought stress using PEG-6000. Results: It was found that aridity caused a significant increase in the content of osmotic stress substances and antioxidant enzyme activity. The content of malondialdehyde (MDA) in QS was lower than that in LD and GN under moisture stress, indicating a stronger accumulation capacity of osmotic regulatory substances. Based on sequencing results, 14,475, 9336, and 9243 upregulated DEGs from QS, LD, and GN were annotated into 26, 29, and 28 transcription factor families, respectively. QS showed more DEGs than LD and GN. KEGG enrichment analysis identified that DEGs were significantly enriched in metabolic pathways such as amino acid biosynthesis, phenylpropanoid biosynthesis, plant hormone signaling transduction, and MAPK pathways. This suggests a strong correlation between these pathways and drought stress. The results also show that genes associated with ABA hormone signaling (MS. gene93372, MS. gene072046, and MS. gene012975) are crucial for plant's adaptation to drought stress. Conclusions: These genes, such as serine/threonine protein kinases and abscisic acid receptors, play a crucial role in plant hormone signaling and MAPK pathways. They could serve as potential candidate genes for drought resistance research in alfalfa, providing a molecular foundation for studying drought resistance. [ABSTRACT FROM AUTHOR]

Bitter gourd is an economically important horticultural crop for its edible and medicinal value. However, the regulatory mechanisms of bitter gourd in response to cold stress are still poorly elucidated. In this study, phytohormone determination and comparative transcriptome analyses in XY (cold-tolerant) and QF (cold-sensitive) after low temperature treatment were conducted. Under cold stress, the endogenous contents of abscisic acid (ABA), jasmonic acid (JA) and salicylic acid (SA) in XY were significantly increased at 24 h after treatment (HAT), indicating that ABA, JA and SA might function in regulating cold resistance. RNA-seq results revealed that more differentially expressed genes were identified at 6 HAT in QF and 24 HAT in XY, respectively. KEGG analysis suggested that the plant hormone signal transduction pathway was significantly enriched in both genotypes at all the time points. In addition, transcription factors showing different expression patterns between XY and QF were identified, including CBF3, ERF2, NAC90, WRKY51 and WRKY70. Weighted gene co-expression network analysis suggested MARK1, ERF17, UGT74E2, GH3.1 and PPR as hub genes. These results will deepen the understanding of molecular mechanism of bitter gourd in response to cold stress and the identified genes may help to facilitate the genetic improvement of cold-resistant cultivars. [ABSTRACT FROM AUTHOR]

Transcription factor MYB is a critical factor involved in anthocyanin biosynthesis and abiotic stress resistance of plants. This paper reports the functions of codon-optimized transcription factor VvMYBA6 expressed in transgenic Arabidopsis plants. VvMYBA6 overexpression resulted in significant increase of anthocyanin content, which also enhanced salt and mannitol tolerance in transgenic Arabidopsis plants. Besides, real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of VvMYBA6 promoted the expression level of genes involved in anthocyanin biosynthesis, abscisic acid (ABA) synthesis, proline synthesis, stress responses and ROS scavenging under salt and mannitol stress. According to further analysis under salt and mannitol stress, overexpression of VvMYBA6 significantly increased ABA and proline content, activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as reduced the content of HO and malonaldehyde (MDA). The results demonstrated that the overexpression of VvMYBA6 enhanced salt and mannitol tolerance based on increasing synthetic levels of anthocyanin and ABA in transgenic Arabidopsis plants. Therefore, the overexpression of VvMYBA6 could be widely used in promoting salt tolerance in plants. [ABSTRACT FROM AUTHOR]

Induced resistance is considered an eco-friendly disease control strategy, which can enhance plant disease resistance by inducing the plant's immune system to activate the defense response. In recent years, studies have shown that lactic acid can play a role in plant defense against biological stress; however, whether lactic acid can improve tobacco resistance to Phytophthora nicotianae, and its molecular mechanism remains unclear. In our study, the mycelial growth and sporangium production of P. nicotianae were inhibited by lactic acid in vitro in a dose-dependent manner. Application of lactic acid could reduce the disease index, and the contents of total phenol, salicylic acid (SA), jasmonic acid (JA), lignin and H2O2, catalase (CAT) and phenylalanine ammonia–lyase (PAL) activities were significantly increased. To explore this lactic acid-induced protective mechanism for tobacco disease resistance, RNA-Seq analysis was used. Lactic acid enhances tobacco disease resistance by activating Ca2+, reactive oxygen species (ROS) signal transduction, regulating antioxidant enzymes, SA, JA, abscisic acid (ABA) and indole-3-acetic acid (IAA) signaling pathways, and up-regulating flavonoid biosynthesis-related genes. This study demonstrated that lactic acid might play a role in inducing resistance to tobacco black shank disease; the mechanism by which lactic acid induces disease resistance includes direct antifungal activity and inducing the host to produce direct and primed defenses. In conclusion, this study provided a theoretical basis for lactic acid-induced resistance and a new perspective for preventing and treating tobacco black shank disease. [ABSTRACT FROM AUTHOR]

Low-temperature germination (LTG) is an important agronomic trait for rice (Oryza sativa). Japonica rice generally has greater capacity for germination at low temperatures than the indica subpopulation. However, the genetic basis and molecular mechanisms underlying this complex trait are poorly understood. Here, we report that OsUBC12, encoding an E2 ubiquitin-conjugating enzyme, increases low-temperature germinability in japonica, owing to a transposon insertion in its promoter enhancing its expression. Natural variation analysis reveals that transposon insertion in the OsUBC12 promoter mainly occurs in the japonica lineage. The variation detected in eight representative two-line male sterile lines suggests the existence of this allele introgression by indica-japonica hybridization breeding, and varieties carrying the japonica OsUBC12 locus (transposon insertion) have higher low-temperature germinability than varieties without the locus. Further molecular analysis shows that OsUBC12 negatively regulate ABA signaling. OsUBC12-regulated seed germination and ABA signaling mainly depend on a conserved active site required for ubiquitin-conjugating enzyme activity. Furthermore, OsUBC12 directly associates with rice SUCROSE NON-FERMENTING 1-RELATED PROTEIN KINASE 1.1 (OsSnRK1.1), promoting its degradation. OsSnRK1.1 inhibits LTG by enhancing ABA signaling and acts downstream of OsUBC12. These findings shed light on the underlying mechanisms of UBC12 regulating LTG and provide genetic reference points for improving LTG in indica rice. Japonica rice generally has greater capacity for low temperatures germination (LTG) than indica rice. Here, the authors report an E2 ubiquitin-conjugating enzyme-encoding gene OsUBC12 can increase LTG in japonica rice by negatively regulate ABA signaling via promoting the proteasomal degradation of OsSnRK1.1. [ABSTRACT FROM AUTHOR]

Leaf angle, as one of the important agronomic traits of maize, can directly affect the planting density of maize, thereby affecting its yield. Here we used the ZmLPA1 gene mutant lpa1 to study maize leaf angle and found that the lpa1 leaf angle changed significantly under exogenous brassinosteroid (BR) treatment compared with WT (inbred line B73). Transcriptome sequencing of WT and lpa1 treated with different concentrations of exogenous BR showed that the differentially expressed genes were upregulated with auxin, cytokinin and brassinosteroid; Genes associated with abscisic acid are down-regulated. The differentially expressed genes in WT and lpa1 by weighted gene co-expression network analysis (WGCNA) yielded two gene modules associated with maize leaf angle change under exogenous BR treatment. The results provide a new theory for the regulation of maize leaf angle by lpa1 and exogenous BR. [ABSTRACT FROM AUTHOR]

Translation of seed stored mRNAs is essential to trigger germination. However, when RNAPII re-engages RNA synthesis during the seed-to-seedling transition has remained in question. Combining csRNA-seq, ATAC-seq and smFISH in Arabidopsis thaliana we demonstrate that active transcription initiation is detectable during the entire germination process. Features of non-coding regulation such as dynamic changes in chromatin accessible regions, antisense transcription, as well as bidirectional non-coding promoters are widespread throughout the Arabidopsis genome. We show that sensitivity to exogenous ABSCISIC ACID (ABA) during germination depends on proximal promoter accessibility at ABA-responsive genes. Moreover, we provide genetic validation of the existence of divergent transcription in plants. Our results reveal that active enhancer elements are transcribed producing non-coding enhancer RNAs (eRNAs) as widely documented in metazoans. In sum, this study defining the extent and role of coding and non-coding transcription during key stages of germination expands our understanding of transcriptional mechanisms underlying plant developmental transitions. Seed germination in plants is a tightly controlled process relying on translation of stored RNAs. Here, Tremblay et al. show that nascent transcriptome and epigenome reprogramming are detected from initial stages of germination. [ABSTRACT FROM AUTHOR]

To explore the fruit-cracking mechanism in nectarine, we compared three cracking-susceptible nectarine varieties ('Huaguang', 'Yanguang', and 'Zaohongzhu') and one cracking-resistant nectarine variety ('Shuguang'). Our findings indicate that 'Shuguang' nectarines exhibited significantly higher levels of calcium, calcium pectinate, total pectin, cellulose, Na2CO3-soluble pectin and CDTA-soluble pectin in the peel compared to 'Huaguang', 'Yanguang', and 'Zaohongzhu'. In contrast, the activities of polygalacturonases, pectinesterases, β-galactosidases, and cellulase were significantly lower in 'Shuguang'. Interestingly, no significant differences were observed in indole-3-acetic acid and gibberellic acid content between 'Shuguang' and the other three cracking-susceptible nectarine varieties. However, the abscisic acid content in 'Shuguang' was significantly lower. Additionally, compared with the three cracking-susceptible nectarine varieties, the expression level of PpPIP1 (encoding the plasma membrane intrinsic protein, which can improve the permeability of plant cell membranes and greatly improve the efficiency of water diffusion across membranes) in flesh was significantly lower, and the expression levels of PpExp1 and PpExp2 (encoding expansins, which play significant roles in loosening and expanding cell wall components) were significantly higher in the peels of cracking-resistant nectarine varieties. These differences can provide a basis for further study of the mechanism of nectarine fruit-cracking. [ABSTRACT FROM AUTHOR]

Plant yield is severely hampered by drought, affirming the urgent need to develop strategies to improve plant growth and drought tolerance. The synergistic application of ABA and calcium nanoparticles (Ca-NPs) has emerged as a promising approach for sustainable crop production and improved resistance to abiotic stress, although the underlying mechanism for foliar application of growth regulator ABA and Ca-NPs in regulating plant growth and drought tolerance in rapeseed (Brassica napus L.) remains poorly understood. To address this knowledge gap, the current study was conducted to investigate the protective role of 100-µM ABA and 100 ppm Ca-NPs in alleviating the drought stress (15% PEG-6000) in B. napus following further application with 100 µM solution of photosynthesis inhibitor 3-(3,4-dichlorophyllorophenyl)-1,1-dimethylurea (DCMU). Foliar application of 100 ppm Ca-NPs and 100-µM ABA significantly reduced the drought stress by increasing chl a, chl b, total chlorophyll, carotenoids, xanthophyll by 86, 63, 78, 56, 68%; nutritional profile Ca, K, P, Mg, Mn, B by 131, 108, 98, 111, 82, 67% of B. napus plants, respectively. Moreover, under drought condition the combined treatment of Ca-NPs + ABA along with the DCMU increased the Pn, Gs, Ci, Tr by 30, 24, 37, 22% and transcript abundance of transcription factors and ROS homeostasis genes (CDPK5, MYC2, TGA1, CAS, and POD), and photosynthetic proteins expressions (NCED3, PsbB, CP29, CP24, PCaA, CP26 and cytochrome f). Overall, this study provides the evidence of effectiveness of combined application of Ca-NPs and ABA in alleviating drought stress in rapeseed. [ABSTRACT FROM AUTHOR]

Guttation is one of several visible physiological events of plant kingdom. The mechanism of this phenomenon is however, obscure and embedded deep into mysteries despite its vital significance for the plants and people. In this paper attempts have been made, in the light of recent discoveries, and new and novel findings, to review the past and present works reflecting on an integrated view of the mechanism of this phenomenon and its regulation. In this context, the gene transfer technology and other modern developments in instrumentation and experimentation have enabled to a large extent the understanding of the mechanism of plant secretion of liquid having solutes, both organic and inorganic, dissolved in it. In all probability, this process seems to originate primarily on account of root pressure that involves osmotic withdrawal and transport of water from growth medium and subsequently activities of living cells of xylem parenchyma at the expense of energy fuelled by ATP leading to energetically uphill co-transport of water and solutes in xylem vessels building hydrostatic pressure in the roots pushing the saps upward (Wegner in Journal of Experimental Botany 65:381-393, ; Singh ). This process though genetically governed, appears to be triggered and regulated by the interaction of several internal, external and edaphic factors finely-tuned by chemico-mechanosensors such as pH gradient, hormones, mechanical loading, turgor potential, membrane potential, temperature, light, touch, sound etc. influencing cellular contractile proteins and gating of aquaporins. The positive hydrostatic pressure so developed is, in turn, transmitted via stem to the leaves as release of water droplets of guttation through permanently open hydathodes located at the tips, margins, adaxial and abaxial surfaces of uninjured leaves. [ABSTRACT FROM AUTHOR]

Mevalonate diphosphate decarboxylase (GbMVD) of Ginkgo biloba catalyzes the final step of mevalonic acid pathway by converting the six-carbon mevalonate diphosphate into isopentenyl diphosphate, a precursor of ginkgolides and bilobalide collectively termed terpene trilactones (TTLs). This paper presents the isolation of a 1.2-kb fragment (designated as GbMVDpro) of the 5′-flanking region of GbMVD. Extensive sequence analysis revealed the presence of evolutionarily conserved putative cis-acting elements in light-regulated transcription, hormone signaling (abscisic acid, jasmonate, and salicylic acid), and plant defense (W-box/WRKY) in the GbMVD promoter region. Electrophoretic mobility shift analysis suggested possible involvement of W-box in GbMVD promoter function. To assess the organ-specific and environmentally responsive characteristics of GbMVD expression, GbMVDpro was fused to GUS reporter gene. GbMVDpro::GUS was introduced into tobacco. Histological analysis of the transgenic tobacco showed that GUS mainly localized in the leaf epidermis, stem secondary xylem, and root vasculature. These observations closely correlated with the previously reported presence of GbMVD transcripts in the roots, stems, and leaves. Further functional characterizations in transiently transformed tobacco leaves allowed us to identify the region that can be considered as the minimal promoter. Light and hormonal signals (i.e., ethephon, salicylic acid, and methyl jasmonate) induced the activity of GbMVDpro-driven GUS in transgenic tobacco and enhanced the transcription of GbMVD as well as TTL production in ginkgo seedlings. These results, together with the bioinformatic analysis of GbMVDpro, suggest that the GbMVD promoter harbored a numerous TTL biosynthesis-related cis-elements that regulate the flux of terpenoid precursors. [ABSTRACT FROM AUTHOR]

In this paper, the formation mechanism of the abscisic acid (ABA) transport channel in protein PYL2 was studied by the molecular dynamics (MD) method. MD simulations suggested that CL2, CL3 and CL4 loops in PYL2 are more flexible than other loops after the PYL2 activation. ABA binding induces dramatic conformational changes in loops CL2, CL2 and CL3, which indicates that the three loops may play key roles in the activation of the channel for the ABA entry into the pocket of the PYL2 protein. Simulations also showed that residue Arg120 in CL3 plays an essential role in the formation of the ABA transport channel. In SMD simulations, a steady increase of the applied force during the first 400 ps of the ABA egress process was shown. It rose to approximately 680 pN that was the maximum rupture force of the ABA unbinding along this pathway. The large rupture force may contribute to the breaking of hydrogen bonds between ABA and PYL2. [ABSTRACT FROM AUTHOR]

Effect of presowing treatment with stevioside (10–8 M) on activity, content, and expression of the wheat-germ agglutinin (WGA) gene, as well as the content of phytohormones, was studied in 4-day-old seedlings of wheat (Triticum aestivum L.) exposed to low above-zero temperatures. Pretreatment with stevioside considerably increased the protective potential of plants in response to low-temperature stress. The obtained results point to an ABA-dependent effect of stevioside on WGA in spite of the gibberellin-like chemical structure of the examined growth regulator. [ABSTRACT FROM AUTHOR]

Background: Raising global temperatures limit crop productivity and new strategies are needed to improve the resilience of thermosensitive crops such as potato (Solanum tuberosum L.). Biostimulants are emerging as potential crop protection products against environmental stress, however their mechanism of action remains largely unknown, hindering their wider adoption. We used comprehensive physiological, molecular, and mass spectrometry approaches to develop understanding of the mechanism of plant thermotolerance exerted by the biostimulant, Quantis™, under heat stress. Using orthologues gene mutations in Arabidopsis thaliana we report heat-defence genes, modified by Quantis™, which were also investigated for potential overlapping functions in biotic stress defence to Sclerotinia sclerotiorum and Rhizoctonia solani. Results: Quantis™ enhanced PSII photochemical efficiency and decreased thermal dissipation of potato grown under heat stress. These effects were associated with upregulation of genes with antioxidant function, including PR10, flavonoid 3′‐hydroxylase and β-glucosidases, and modulation of abscisic acid (ABA) and cytokinin (CK) activity in leaves by Quantis™. The biostimulant modulated the expression of the heat-defence genes, PEN1, PR4 or MEE59, with functions in leaf photoprotection and root thermal protection, but with no overlapping function in biotic stress defence. Protective root growth under heat stress, following the biostimulant application, was correlated with enhanced CK signalling in roots. Increased endogenous concentrations of ABA and CK in potato leaves and significant upregulation of StFKF1 were consistent with tuberisation promoting effects. Quantis™ application resulted in 4% tuber weight increase and 40% larger tuber size thus mitigating negative effects of heat stress on tuber growth. Conclusions: Quantis™ application prior to heat stress effectively primed heat tolerance responses and alleviated temperature stress of S. tuberosum L. and A. thaliana by modulating the expression and function of PR4 and MEE59 and by regulating CK activity above and below ground, indicating that the mechanism of action of the biostimulant is conserved, and will be effective in many plant species. Thus, a biostimulant application targeting the most susceptible crop developmental stages to heat disorders can be effectively integrated within future agronomy practices to mitigate losses in other thermosensitive crops. [ABSTRACT FROM AUTHOR]

Background: With the increasing frequency of climatic anomalies, high temperatures and long-term rain often occur during the rice-harvesting period, especially for early rice crops in tropical and subtropical regions. Seed dormancy directly affects the resistance to pre-harvest sprouting (PHS). Therefore, in order to increase rice production, it is critical to enhance seed dormancy and avoid yield losses to PHS. The elucidation and utilization of the seed dormancy regulation mechanism is of great significance to rice production. Preliminary results indicated that the OsMKKK62-OsMKK3-OsMPK7/14 module might regulate ABA sensitivity and then control seed dormancy. The detailed mechanism is still unclear. Results: The overexpression of OsMKK3 resulted in serious PHS. The expression levels of OsMKK3 and OsMPK7 were upregulated by ABA and GA at germination stage. OsMKK3 and OsMPK7 are both located in the nucleus and cytoplasm. The dormancy level of double knockout mutant mkk3/mft2 was lower than that of mkk3, indicating that OsMFT2 functions in the downstream of MKK3 cascade in regulating rice seeds germination. Biochemical results showed that OsMPK7 interacted with multiple core ABA signaling components according to yeast two-hybrid screening and luciferase complementation experiments, suggesting that MKK3 cascade regulates ABA signaling by modulating the core ABA signaling components. Moreover, the ABA response and ABA responsive genes of mpk7/14 were significantly higher than those of wild-type ZH11 when subjected to ABA treatment. Conclusion: MKK3 cascade mediates the negative feedback loop of ABA signal through the interaction between OsMPK7 and core ABA signaling components in rice. [ABSTRACT FROM AUTHOR]

Acetylcholine (ACh), a potential plant growth regulator, can alleviate injury caused by NaCl and cadmium stress. However, the underlying mechanisms whereby it affects seed germination remain unclear. We pre-soaked maize (Zea mays L.) in different concentrations (1–3 μm) of ACh. Seed germination and levels of β-galactosidase, α-amylase, and starch were analyzed. ACh, abscisic acid (ABA), and gibberellic acid levels were estimated via enzyme-linked immunosorbent assay. The expression of ABA and gibberellic acid signaling-related genes was analyzed. Salt stress significantly reduced seed germination and hypocotyl elongation but increased ABA and H2O2 levels and enhanced antioxidant enzyme activity. Priming with 2 μm ACh caused a significantly higher germination rate (by 13.4%) relative to that of the seeds subjected to salt stress alone. Under salt stress, ACh effectively upregulated α-amylase and β-galactosidase activity (by 0.63- and 1.04-fold) and reduced starch content (by 34.02%). ACh treatment downregulated the expression of ZmNCED3 (involved in ABA signaling) and upregulated that of ZmKAO (involved in gibberellin signaling). The leaves of the seedlings pretreated with ACh presented higher antioxidant enzyme activity and, therefore, lower H2O2 accumulation than those of seedlings subjected to salt stress alone. Priming the maize seeds with exogenous ACh maintained seedling growth under salt stress. ACh pretreatment increased antioxidant activity, reduced ABA activity, and improved salt tolerance in maize seeds exposed to salt stress. These findings suggest that pretreatment with 2 μm ACh improves seed germination, activates ROS scavenging, and regulates phytohormone levels under salt stress, thereby improving growth. [ABSTRACT FROM AUTHOR]

Non-hydraulic root signals (nHRS) are affirmed as a unique positive response to soil drying, and play a crucial role in regulating water use efficiency and yield formation in dryland wheat production. Strigolactones (SLs) can enhance plant drought adaptability. However, the question of whether strigolactones enhance grain yield and water use efficiency by regulating nHRS and antioxidant defense systems in dryland wheat remains unanswered. In this study, pot experiments were conducted to investigate the effects of strigolactones on nHRS, antioxidant defense system, and grain yield and water use efficiency in dryland wheat. The results showed that external application of SLs increased drought-induced abscisic acid (ABA) accumulation and activated an earlier trigger of nHRS at 73.4% field capacity (FC), compared to 68.5% FC in the control group (CK). This phenomenon was mechanically associated with the physiological mediation of SLs. The application of SLs significantly enhanced the activities of leaf antioxidant enzymes, reduced ROS production, and mitigated oxidative damage to lipid membrane. Additionally, root biomass, root length density, and root to shoot ratio were increased under strigolactone treatment. Furthermore, exogenous application of SLs significantly increased grain yield by 34.9% under moderate drought stress. Water use efficiency was also increased by 21.5% and 33.3% under moderate and severe drought conditions respectively, compared to the control group (CK). The results suggested that the application of strigolactones triggered earlier drought-sensing mechanism and improved the antioxidant defense ability, thus enhancing grain yield and water use efficiency in dryland wheat production. [ABSTRACT FROM AUTHOR]

Seed germination is a complex process regulated by internal and external factors. Melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous signaling molecule, playing an important role in regulating seed germination under normal and stressful conditions. In this review, we aim to provide a comprehensive overview on melatonin's effects on seed germination on the basis of existing literature. Under normal conditions, exogenous high levels of melatonin can suppress or delay seed germination, suggesting that melatonin may play a role in maintaining seed dormancy and preventing premature germination. Conversely, under stressful conditions (e.g., high salinity, drought, and extreme temperatures), melatonin has been found to accelerate seed germination. Melatonin can modulate the expression of genes involved in ABA and GA metabolism, thereby influencing the balance of these hormones and affecting the ABA/GA ratio. Melatonin has been shown to modulate ROS accumulation and nutrient mobilization, which can impact the germination process. In conclusion, melatonin can inhibit germination under normal conditions while promoting germination under stressful conditions via regulating the ABA/GA ratios, ROS levels, and metabolic enzyme activity. Further research in this area will deepen our understanding of melatonin's intricate role in seed germination and may contribute to the development of improved seed treatments and agricultural practices. [ABSTRACT FROM AUTHOR]

Abiotic stresses in wheat, particularly drought (DR), hamper wheat production and causes up to 86% yield losses. Therefore, developing stress-tolerant genotypes is a major challenge in wheat breeding. In this study, we evaluated 72 diverse wheat genotypes for DR tolerance over two consecutive years, examining 12 morpho-physiological traits under irrigated (IR) and DR conditions. Under DR, grain yield (GY) was significantly associated with biomass and phenological traits. The principal component analysis accounted for 82.79% and 80.08% of the overall variation during IR and DR stress conditions, respectively. Based on GY component traits and drought susceptible index, two tolerant (IC36761A and IC128335) and two susceptible (IC138852 and IC335732) genotypes were selected for physio-biochemical analysis. In these genotypes, the membrane stability index (MSI) ranged from 57 to 74% and 35 to 64% under IR and DR conditions. Genotype IC128335 showed 78.10% relative water content (RWC), 2.97 mg/g tannin, and 3.67 mg/g fresh weight reducing sugar (RS) content under DR conditions. Abscisic acid (ABA) content ranged from 0.81 to 4.03 ppm/g dry weight (DW) and 0.92–4.23 ppm/g DW under IR and DR stress conditions, respectively. There was a significant genotype × environment interaction observed for the physio-biochemical traits. The genotypes IC36761A and IC128335 suffered less reduction in MSI and RWC. RS and flavonoid content significantly increased in all four genotypes, but the tannin and ABA levels increased especially in IC128335 and IC36761A under DR conditions. The physio-biochemical findings support the DR tolerance of genotypes IC128335 and IC36761A, indicating their potential for inclusion in breeding programs aimed at enhancing DR tolerance in bread wheat. [ABSTRACT FROM AUTHOR]

This article discusses a study on the enzyme GAS2 and its role in the breakdown of abscisic acid (ABA), a plant hormone involved in stress responses. The study found that GAS2 converts ABA and its precursor, phaseic acid (PA), into a compound called 8'-carboxy-ABA. The researchers also observed that increased levels of GAS2 resulted in lower ABA levels and reduced sensitivity to ABA in Arabidopsis plants. These findings suggest that GAS2 plays a significant role in the breakdown of ABA and may impact how plants respond to stress. [Extracted from the article]

This research aimed toward bioengineering of Zinc oxide nanoparticles (ZnO NPs) using Rosa canina L. aqueous extract followed by conjugation with Abscisic acid (ABA) for inducing drought-tolerant properties in Zea mays L under water stress. The impact of six different treatments using seed imbibition (SI) and foliar spray (FS) methods upon physio-morphological and biochemical properties of Z. mays L. was studied. These included ABA-SI, ABA-FS, ABA-ZnO-SI, ABA-ZnO-FS, ZnO-SI, and ZnO-FS, drought control (DC), and untreated healthy control (HC). Both ZnO and ABA-ZnO NPs showed distinct UV–Visible peaks at 438 nm and 339 nm with mean sizes of 20.17 nm and 14.05 nm, respectively. Scanning Electron Microscopy coupled with Energy-Dispersive X-ray identified 60.14% Zn in ZnO NPs with irregular surface topology and 56.72% Zn in ABA-ZnO NPs with semi-cylindrical morphology. Among treated maize plants, ABA-ZnO-SI displayed prominent results with increased root length (32.89 ± 1.25 cm), relative water content (20.4 ± 2.9%), total chlorophyll content [10.73 ± 0.18 mgg−1 Fresh weight (FW)], carotenoid content (190.4 ± 0.56 mg g−1 FW), cob length (27.94 ± 1.32 cm), cob weight (25.64 ± 0.42 g), and short anthesis-silking interval (3 days). Stomatal opening (0.95 ± 0.24%) and leaf damage index (29.86 ± 0.19%) were reduced in ABA-ZnO-SI treatment compared to DC. A significant amount of proline (4.40 ± 0.01 µmoles g−1 FW) with reduced lipid peroxidation (0.24 ± 0.02-mM malondialdehyde) and highest antioxidant activities (IC50: 332.8 ± 0.46 µg/ml) with maximum levels of catalase (2.87 ± 0.05 Uml−1), ascorbate peroxidase (3.41 ± 0.02 Uml−1), and guaiacol peroxidase (3.10 ± 0.06 Uml−1) were observed in ABA-ZnO-SI-treated plants. Given the promising outcomes, current research work has brought forward a potential drought tolerance treatment for Z. mays L. which might serve as productive agricultural progress in upcoming years. [ABSTRACT FROM AUTHOR]

Sorghum (Sorghum bicolor L. Moench) is one of the most significant cereals worldwide. Its growth and yield are threatened by different abiotic stresses, particularly drought and salinity. In this study, we performed a comprehensive meta-analysis on sorghum using RNA-seq data to discover differentially expressed genes effective in responses to drought and salinity stresses. The meta-analysis identified 2139 and 2238 genes for drought, and salinity stresses significantly differentially expressed in control and stress conditions, respectively. Also, the 1835 genes were common under drought and salinity stress conditions. Gene ontology and Kyoto encyclopedia of genes and genomes pathway enrichment analysis showed that differentially expressed genes are significantly enriched in photosynthesis and metabolic pathways, response to abiotic stimulus, phosphorus metabolic process, and biosynthesis of secondary metabolites. We found 96 transcription factor genes, all classified into 28 transcription factor families. Also, 217 protein kinase genes were recognized, with the plant receptor-like kinase (RLK-Pelle) family as the largest category. Besides, the promoter analysis identified 68 significant cis-acting elements in the hub gene's upstream regions. Known cis-acting elements participate in light-responsive, hormone-responsive, stress-related, tissue and development-related, and promoter and site-binding-related elements. Weighted gene co-expression network analysis identified 11 and 6 distinct co-expression modules for drought and salinity stresses, respectively, mainly associated with genes in response to temperature stimulus, photosynthesis, phosphorus metabolic process, and abscisic acid. The network analysis also identified hub genes, including SORBI_3001G410100, SORBI_3002G343500, SORBI_3001G426900, SORBI_3010G246000, and SORBI_3004G293500 involved in regulating the stress response. These findings provide novel insights into the abiotic stress molecular response and introduce numerous candidate genes, offering evidence for subsequent analysis of validation of their biological functions to unravel the molecular mechanisms of abiotic tolerance in sorghum. [ABSTRACT FROM AUTHOR]

Water stress is a primary abiotic stress that produces several morphological, physiological, biochemical and molecular alterations, which affect crop productivity. The aim of the present study was to evaluate and compare morphophysiological and biochemical characteristics and the hormone profiles of two sunflower inbred lines (C803 and R461-4) in response to moderate water stress at the early vegetative growth (V2) stage. Sunflower seedlings of C803 and R461-4 inbred lines obtained in pots filled with sand moistened to 60% field capacity were watered with (1) Hoagland's solution (control) or (2) mannitol 400 mM (moderate water stress) to field capacity on the fourth day after sowing. At V2, the seedlings were harvested and sectioned into the aerial part and roots. The parameters recorded for the analyses included the aerial part and root length, fresh and dry weight, leaf area and expansion rate, stomatal conductance, osmotic potential, phytohormones and total soluble carbohydrates. Among these parameters, the leaf area and stomatal conductance were the most affected by water stress. Abscisic acid and salicylic acid showed significant increases in the aerial part of water-stressed seedlings, while abscisic acid was the most abundant phytohormone in the roots. In addition, 28-Homocastasterone was the brassinosteroid with higher levels in both lines. This is the first report of teasterone in the sunflower. Finally, total soluble carbohydrates increased upon stressful conditions. Altogether, the water stress led to different parameter alterations dependent on the inbred line and its different sensitivity to water stress. [ABSTRACT FROM AUTHOR]

Herbaceous peony is a perennial root plant that likes light and is cold-resistant. During summer, high temperature and strong light intensity advance its entry into the leaf wilting stage, which limits the accumulation of nutrients and formation of strong buds and severely affects its growth and development the following year. In this study, the wild herbaceous peony species and two main cultivars, 'Zifengyu' and 'Hongfengyu', were subjected to slight shading and strong light environments in summer, and their effects on leaf senescence and endogenous hormone and polyamine contents were explored. Slight shading treatment significantly delayed withering, increased the leaf net photosynthetic rate, and increased the chlorophyll, soluble sugar, indole-3-acetic acid, zeatin, gibberellin, spermine, spermidine, putrescine, and polyamine contents. Additionally, slight shading significantly reduced the proline and abscisic acid contents. Slight shading during summer prolonged the green period and delayed leaf senescence. The tolerance of tested materials to strong light intensity in summer was ranked as follows: 'Zifengyu' > 'Hongfengyu' > wild species. In conclusion, this study revealed that summer leaf senescence is delayed in herbaceous peony through shading and growth regulators. Additional varieties should be evaluated to provide reference for high-efficiency, high-quality, and high-yield cultivation of herbaceous peony. [ABSTRACT FROM AUTHOR]

Global warming is a critical challenge limiting crop productivity. Heat stress during cucumber growing stages caused deterioration impacts on the flowering, fruit, and yield stages. In this study, "inbred line 1 and hybrid P1 × P2" (heat-tolerant) and "Barracuda" (heat-sensitive) were utilized to determine the heat tolerance in summer season. The heat injury index was used to exhibit the heat tolerance performance. The heat injury index for heat tolerant (HT) genotypes, on leaves (HIIL%) and female flowers (HIIF%), was less than 25 and 15 % in HT, compared to heat sensitive (HS) was more than 75 and 85%, respectively. Moreover, the content of leaf chlorophyll, proline, brassinosteroid (BRs), abscisic acid content (ABA), the activity of catalase (CAT, EC 1.11. 1.6), peroxidase (POD, EC 1.11.1.7) and superoxide dismutase (SOD, EC 1.15.1.1) increased with the heat stress responses in HT plants. Expression pattern analyses of eight genes, related to POD (CSGY4G005180 and CSGY6G015230), SOD (CSGY4G010750 and CSGY1G026400), CAT (CsGy4G025230 and CsGy4G025240), and BR (CsGy6G029150 and CsGy6G004930) showed a significant increase in HT higher than in HS plants. This study furnishes valuable markers for heat tolerance genotypes breeding in cucumber and provides a basis for understanding heat-tolerance mechanisms. [ABSTRACT FROM AUTHOR]

Cryopreservation is an important technique used in the conservation of various plant tissues. This study proposes a cryopreservation method for the long-term conservation of eastern bracken fern gametophytes (Pteridium aquilinum var. latiusculum). Encapsulation–dehydration of the gametophytes was performed, and the exogenous sucrose and abscisic acid (ABA) preculture conditions were investigated. Gametophytes are sensitive to dehydration and drying, and the following treatment conditions were applied: encapsulation by alginate containing 0.75 M sucrose, 18-h loading treatment with 0.75 M sucrose, and 6-h drying treatment. The survival rate following cryopreservation was determined. The water content of < 27.5% in the alginate beads after dehydration and drying was found to be appropriate for ensuring survival. Additionally, performing an exogenous sucrose and ABA preculture was essential before encapsulation to achieve a survival of ≥ 90%. The high stress induced by cryopreservation and exogenous preculture regulated the expression of PaSuSy, PaLEA14, and PaABI1b and the endogenous ABA content. In eastern bracken gametophytes, ABI1 appears to be a negative regulator of ABA signaling. These results indicate that the encapsulation–dehydration method is effective for the long-term conservation of eastern bracken fern gametophytes, and exogenous preculture alleviates abiotic stress and increases the survival rate. [ABSTRACT FROM AUTHOR]

Abies koreana, a plant species endemic to Korea, is sensitive to climate change. However, little is known about the molecular mechanisms underlying its environmental stress response. Here, we characterized the effects of exogenous abscisic acid (ABA) concentration, application method, and application duration on the expression of ABA-responsive genes in A. koreana. The expression level of AkNAC19 was significantly higher in ABA (0.2, 0.4, 0.8 mM)-treated leaves (needles) than in non-treated samples, indicating the role of ABA in the induction of gene expression. In addition, 0.2 mM ABA was found to be optimal for gene regulation. When assessing the efficacies of ABA application methods, the dipping method was slightly more effective in inducing gene expression than the pressure method. Therefore, leaves were further treated with 0.2 mM ABA using the dipping method to investigate the expression levels of multiple ABA-responsive genes, including AkNAC19, AkMPK6, AkERF4, AkNAC2, AkbHLH, AkEFP, AkHSP17.6, and AkMYB123. The expression levels of all genes, except AkMPK6, were significantly higher in ABA-treated leaves than in non-treated leaves. However, the optimal treatment duration for gene expression induction varied with the gene type. Overall, these results suggest that A. koreana responds to abiotic stress by upregulating the expression of ABA-responsive genes. [ABSTRACT FROM AUTHOR]

In response to the rapid expansion of the worldwide population, there is an urgent need for the development of new, more environmentally-conscious, food sources. In this context, microalgae, such as Euglena, are of interest due to their capacity for large-scale cultivation and flexible bioproduct output. Media recycling techniques have been proposed as waste- and cost-reducing measures for large-scale algal cultivation. Culture dynamics and phytohormone production during novel fermentation conditions can enhance growth and biomass production; yet, little is known about the impacts on growth regulating phytohormones such as cytokinins (CKs) and abscisic acid (ABA) under these conditions. Using Euglena gracilis, an organic culture medium was recycled at 25, 50 and 75% inclusion rates through multiple growth cycles to evaluate impacts on biomass production and phytohormone profiles. A 25% recycled inclusion rate resulted in biomass accumulation similar to the control over one growth cycle. Subsequent recycled rates and growth cycling reduced E. gracilis biomass accumulation relative to the control, even with cell counts continuing to increase throughout, highlighting that the recycled medium inclusion and the number of repeated culture cycles impacts the biomass output of E. gracilis. Phytohormone analysis indicated that E. gracilis synthesized CKs via the tRNA-degradation pathway with increased hormone levels corresponding to higher recycle rates; ABA increased in the supernatant at higher recycle rates but was not detected in any pellet fractions. This research expands upon the roles of CKs and ABA as signaling molecules and adds guidance for building a suite of conditions specific for industrial product development. [ABSTRACT FROM AUTHOR]

The stress hormone, Abscisic acid (ABA), is crucial for plants to respond to changes in their environment. It triggers changes in cytoplasmic Ca2+ levels, which activate plant responses to external stresses. However, how Ca2+ sensing and signaling feeds back into ABA signaling is not well understood. Here we reveal a calcium sensing module that negatively regulates drought stress via modulating ABA receptor PYLs. Mutants cbl1/9 and cipk1 exhibit hypersensitivity to ABA and drought resilience. Furthermore, CIPK1 is shown to interact with and phosphorylate 7 of 14 ABA receptors at the evolutionarily conserved site corresponding to PYL4 Ser129, thereby suppressing their activities and promoting PP2C activities under normal conditions. Under drought stress, ABA impedes PYLs phosphorylation by CIPK1 to respond to ABA signaling and survive in unfavorable environment. These findings provide insights into a previously unknown negative regulatory mechanism of the ABA signaling pathway, which is mediated by CBL1/9-CIPK1-PYLs, resulting in plants that are more sensitive to drought stress. This discovery expands our knowledge about the interplay between Ca2+ signaling and ABA signaling. ABA signaling and Ca2+ signaling regulatory networks are crucial for how plants respond to drought stress. Here, the authors reported that the functional module of the CBL1/9-CIPK1-PYLs regulatory network plays a negative role in ABA signaling and its response to drought stress. [ABSTRACT FROM AUTHOR]

Drought severely damages crop production, even under conditions so mild that the leaves show no signs of wilting. However, it is unclear how field-grown plants respond to mild drought. Here, we show through six years of field trials that ridges are a useful experimental tool to mimic mild drought stress in the field. Mild drought reduces inorganic phosphate levels in the leaves to activate the phosphate starvation response (PSR) in soybean plants in the field. Using Arabidopsis thaliana and its mutant plants grown in pots under controlled environments, we demonstrate that PSR occurs before abscisic acid response under progressive mild drought and that PSR plays a crucial role in plant growth under mild drought. Our observations in the field and laboratory using model crop and experimental plants provide insight into the molecular response to mild drought in field-grown plants and the relationship between nutrition and drought stress response. Even mild drought impacts crop production significantly. Here, the authors develop an experimental mild drought system induced by ridges in the field and find that phosphate starvation response occurs before ABA response in early mild drought. [ABSTRACT FROM AUTHOR]

With the changing global climate, drought is considered one of the most devastating abiotic factors. Drought not only limits plant productivity by changing growth and development but also alters the microbiome in the rhizosphere. In addition to influencing the root microbes, drought modifies the root exudate's composition and profile in the rhizosphere. Plant health, root exudation, and abundance of soil microbes in the rhizosphere are inter-connected. The composition of root exudate is altered in terms of the abundance of primary metabolites such as sugar, amino acids, and organic acids and secondary metabolites like flavonoids, strigolactones, and terpenoids. Here, we discuss how a plethora of soil microbes may be involved in a feedback mechanism by utilizing root exudate constituents to promote drought tolerance in plants. Furthermore, plant drought tolerance is positively associated with strigolactones (SLs) exudation via coordination with ABA hormone signaling. Lastly, while the collection, sampling, and analysis of root exudates are all promising, we attempted to present advanced methodology and the development of novel processes in the review, which benefited greatly. [ABSTRACT FROM AUTHOR]

Salicylic acid (SA) has multiple functions in plants, either under optimal or environmental stress conditions. In salt-stressed plants, SA in coordination with other plant hormones (e.g., auxins, abscisic acid, gibberellins) and other signaling molecules can take part to the finely tuned regulatory network, to promote the stimulation of plant defenses aimed at counteracting the salt-triggered harmful effects. This review summarizes the most updated literature dealing with the roles of SA in salt-stressed plants with the aim to provide a comprehensive picture about physiological, biochemical and molecular mechanisms mediated by SA during salt stress, to highlight the possible beneficial effect of SA supplementation and to orientate the direction of future research on this topic. [ABSTRACT FROM AUTHOR]

Melatonin and polyamines have been broadly found in multiple physiological processes and in diverse abiotic stresses faced by plants. In various plant species, melatonin-induced regulation of polyamine metabolism has been reported to play a critical role in the manifestation of stress tolerance mechanisms. Exogenous melatonin pretreatment has been shown to elevate the levels of endogenous polyamines through enhanced expression of ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) ultimately resulting in tolerant phenotypes. The melatonin-polyamine modulation activates the antioxidant enzymatic machinery within the plant system that maintains the reactive species levels and alleviates the oxidative burst-associated damage responses. Alternatively, melatonin-mediated polyamine catabolism has been reported to be crucial in minimizing the excess reactive species accumulation under stress conditions. The melatonin-induced balance of polyamine metabolic flux maintains the ionic homeostasis in plant cells under stress conditions. Recent reports highlighted that melatonin-polyamine regulation involves crosstalk with salicylic acid, abscisic acid and ethylene that leads to a complex network of defense activation under stress conditions. This review attempts to highlight the regulatory role of melatonin in the modulation of polyamine metabolism and associated signaling components that confer stress tolerance in plants. The potential hormonal crosstalks involving melatonin-polyamine regulation have also been discussed to provide mechanistic insight into possible underlying mechanisms. This study will assist the current understanding of the uses of melatonin and polyamines as polyfunctional phytoprotectant in the crop production system. [ABSTRACT FROM AUTHOR]

Plant-derived smoke is a source of several butenolide compounds collectively termed, karrikins (KARs). These have been recognized as a recent class of plant growth regulators associated with diverse phenomena especially seed germination, seedling vigor and other photo-morphogenetic responses. Role of KARs in improving the performance of plants exposed to different environmental constraints has been recognized recently. KARs mitigate oxidative stress in plants caused by salinity, drought, shade and heavy metals by modulating antioxidative metabolism (SOD, POX, GR, APX) and up-regulating the expression of various stress related genes in plants. Such a modulation involves an interplay with different transcription factors and endogenous plant growth regulators predominantly auxins, gibberellins, ethylene and abscissic acid. The present article is an attempt to gain a comprehensive understanding regarding the KARs-induced plant responses. Moreover, role of KARs in plant abiotic stress tolerance, perception of KARs in plants, expression of different enzymes and genes involved in abiotic stress mitigation, their cross-talk with other endogenous hormones under normal and chellanging environmental circumstances. [ABSTRACT FROM AUTHOR]

Vigna unguiculata (L.) Walp. (subsp. sesquipedalis) is a legume species, widely cultivated in the tropics. The seeds of the plant show orthodox behavior during development with an initial influx of water from the maternal tissues during early embryogeny but declined in subsequent stages of embryo development. The seed acquire desiccation tolerance during embryo drying stage and remains viable for months. However the fully mature seed germinates within two days of hydration. PGRs play an important role in all these processes, since the levels of various hormones change dramatically during the developmental sequence. Seven classes of major PGRs were simultaneously assayed using LC-MS/MS in order to understand the hormonal dynamics and to establish the possible interactions during the orthodox cowpea seed development and germination. There was a differential accumulation of IAA, GA4, tZ, tZR, JA and cisJ in the early embryogeny stage. These PGRs were down regulated in subsequent stages of embryo development. tZ, GA4 and JA were up-regulated upon water induction during germination. ABA was up-regulated in response to a drop in moisture content showing a peak in the mid-embryogeny and down regulated in all other stages including germination. GA/ABA antagonism was observed during the germination in cowpea. SA was found in exceptionally higher level in all stages of seed development and germination. 24-epiBL was detected in significant levels in all stages of development with two peaking in early and late embryogeny. BA, IBA, metJ, GA3, GA7 and ACC were found in insignificant levels in the seeds. Multiple correlation studies showed a strong positive correlation of IAA and JA with cytokinins (tZ and tZR) indicating possible cross-talk between these PGRs. [ABSTRACT FROM AUTHOR]

Soybean is an important oil crop used as a plant protein and oil resource by humans, worldwide. However, abiotic stresses have significantly inhibiting soybean seed germination and yield. Plant hormones can improve stress tolerance by regulating gene expression and physiological processes. In this study, the effect of exogenous SL (strigolactone) was studied on germination and post-germination attributes of soybean grown under alkaline stress. Alkaline stress showed significant delayed response of the germination process and also reduced the radicle length. The qRT-PCR (real-time quantitative PCR) analysis showed that alkali stress increased the expression levels of GmABF4, GmAAO3, GmABI5, GmNCED5, and GmNCED9 genes in ABA (Abcisic acid) pathways. The exogenous application of SL promoted soybean radicle length. The SL-treated plants were much more tolerant to alkali stress exhibiting higher germination rates, longer radicles, increased fresh weight, and higher catalase enzyme activity as compared to control plants. After alkaline stress, the expression of SL biosynthetic and signaling genes, such as GmD27, GmCCD8, GmMAX2 and GmDAD2, was substantially increased under SL exogenous application while expression patterns of ABA biosynthetic and signaling genes, such as GmABI5, GmNCED9, and GmAAO3, were decreased. In conclusion, these results exhibited a positive role of SL on seed germination attributes via alleviation of ABA-mediated germination inhibition, improved antioxidant system as well as efficient biosynthesis, perception, and signaling of SL hormone. [ABSTRACT FROM AUTHOR]