Abscisic Acid Signal Transduction Research Articles

Receptor-like cytoplasmic kinase OsRLCK241 functions as an important regulator of abscisic acid synthesis and response in rice

As an important receptor-like kinase subfamily in plants, receptor-like cytoplasmic kinases (RLCKs), such as Oryza sativa L. ( Os ) RLCK241 , are critical in the response to abiotic stress conditions. However, the involvement of OsRLCK241 in the abscisic acid (ABA) signal response remains unknown. In this study, we found that OsRLCK241 participates in the ABA response in rice. The results showed that OsRLCK241 transcription was notably induced by ABA in the rice shoot and root in time- and dose-dependent manners. Additionally, β-glucuronidase staining and analysis of subcellular localization demonstrated that O sRLCK241 directly responded to both ABA and salt treatments. Moreover, phenotypic and physiological analyses showed that OsRLCK241 overexpression decreased ABA sensitivity and ABA content relative to the wild-type variant (Kitaake) under salt stress, and OsRLCK241 loss-of-function variants consistently displayed the opposite ABA-sensitivity phenotype and effects on ABA content. Furthermore, OsRLCK241 overexpression or loss of function modified stomatal patterning under salt stress. Quantitative real-time PCR indicated that the expression of most ABA synthesis-related marker genes, as well as that of genes involved in ABA signal transduction, was altered in both OsRLCK241- overexpressing rice lines and loss-of-function mutants under salt stress. These results suggest that Os RLCK241 is an important regulator of ABA synthesis and response in rice and expand the understanding of plant RLCKs. • Receptor-like cytoplasmic kinases (RLCKs) play key roles in rice abiotic stress responses. • The rice RLCK gene OsRLCK241 was notably induced by ABA in a time and dosage-dependent fashion. • OsRLCK241 altered ABA sensitivity and endogenous ABA content in response to salt stress in rice.

SiMYB19 from Foxtail Millet (Setaria italica) Confers Transgenic Rice Tolerance to High Salt Stress in the Field

Salt stress is a major threat to crop quality and yield. Most experiments on salt stress-related genes have been conducted at the laboratory or greenhouse scale. Consequently, there is a lack of research demonstrating the merit of exploring these genes in field crops. Here, we found that the R2R3-MYB transcription factor SiMYB19 from foxtail millet is expressed mainly in the roots and is induced by various abiotic stressors such as salt, drought, low nitrogen, and abscisic acid. SiMYB19 is tentatively localized to the nucleus and activates transcription. It enhances salt tolerance in transgenic rice at the germination and seedling stages. SiMYB19 overexpression increased shoot height, grain yield, and salt tolerance in field- and salt pond-grown transgenic rice. SiMYB19 overexpression promotes abscisic acid (ABA) accumulation in transgenic rice and upregulates the ABA synthesis gene OsNCED3 and the ABA signal transduction pathway-related genes OsPK1 and OsABF2. Thus, SiMYB19 improves salt tolerance in transgenic rice by regulating ABA synthesis and signal transduction. Using rice heterologous expression analysis, the present study introduced a novel candidate gene for improving salt tolerance and increasing yield in crops grown in saline-alkali soil.

Transcriptome sequencing with nanopore technology for acquiring a deeper understanding of abscisic acid regulation of secondary mechanisms in Salvia miltiorrhiza

The phytohormone abscisic acid (ABA) plays a central role in mediating plant responses to environmental stresses. As a part of the stress response, the biosynthesis of certain secondary metabolites can be triggered by ABA. Salvia miltiorrhiza is a well-known medicinal plant that produces many biologically active components, such as tanshinones and salvianolic acid B. In this study, for the first time, we investigated S. miltiorrhiza transcriptome variations in response to ABA treatment by using Oxford Nanopore Technology (ONT). More than 76 Gb of clean ONT reads were generated from twelve cDNA libraries, and a total of 22,233 genes were detected. The expression pattern of approximately 50% of these genes was changed upon ABA induction, including most genes involved in ABA biosynthesis and ABA signal transduction, which suggests that in plants, multiple ABA signaling-induced cellular processes respond in a coordinated fashion to environmental stress. In addition, in S. miltiorrhiza leaves, ABA can change alternative splicing outputs mainly by reducing intron retention (IR) events through posttranscriptional splicing, which can quickly enhance protein biosynthesis to help plants cope with environmental stresses. Interestingly, ABA can upregulate the expression of genes involved in salvianolic acid biosynthesis but exerts a lesser effect on tanshinone biosynthesis, which indicates the different roles of these two classes of metabolites in response to environmental stresses. A better understanding of the ABA regulatory mechanism and ABA-triggered secondary metabolism will boost our ability to improve herb quality through molecular-assisted breeding, abiotic stress management and chemical manipulation with ABA-based bioactive agents.

Genome-wide identification and expression analysis of the cucumber PYL gene family.

Abscisic acid (ABA) is a very important hormone in plants. It regulates growth and development of plants and plays an important role in biotic and abiotic stresses. The Pyrabactin resistance 1-like (PYR/PYL) proteins play a central role in ABA signal transduction pathways. The working system of PYL genes in cucumber, an important economical vegetable (Cucumis sativus L.), has not been fully studied yet. Through bioinformatics, a total of 14 individual PYL genes were identified in Chinese long ‘9930’ cucumber. Fourteen PYL genes were distributed on six chromosomes of cucumber, and their encoded proteins predicted to be distributed in cytoplasm and nucleus. Based on the phylogenetic analysis, the PYL genes of cucumber, Arabidopsis, rice, apple, Brachypodium distachyon and soybeancould be classified into three groups. Genetic structures and conserved domains analysis revealed that CsPYL genes in the same group have similar exons and conserved domains. By predicting cis-elements in the promoters, we found that all CsPYL members contained hormone and stress-related elements. Additionally, the expression patterns of CsPYL genes were specific in tissues. Finally, we further examined the expression of 14 CsPYL genes under ABA, PEG, salt stress. The qRT-PCR results showed that most PYL gene expression levels were up-regulated. Furthermore, with different treatments about 3h, the relative expression of PYL8 was up-regulated and more than 20 times higher than 0h. It indicated that this gene may play an important role in abiotic stress.

Comparative Analysis of the Transcriptomes of Persisting and Abscised Fruitlets: Insights into Plant Hormone and Carbohydrate Metabolism Regulated Self-Thinning of Pecan Fruitlets during the Early Stage.

Pecan is one of the most popular nut species in the world. The fruit drop rate of the pecan ‘Pawnee’ is more than 57%, with four fruit drop stages, which is very serious. In this study, we conducted transcriptomic profiling of persisting and abscised fruitlets in early fruit development by RNA-seq. A total of 11,976 differentially expressed genes (DEGs) were identified, 3012 upregulated and 8964 downregulated, in a comparison of abscised vs. persisting fruitlets at 35 days after anthesis (DAA). Our transcriptomic data suggest that gene subsets encoding elements involving the biosynthesis, metabolism, perception, signal transduction, and crosstalk of the plant hormones abscisic acid (ABA), auxin, cytokinin, ethylene, and gibberellin (GA) and plant growth regulators jasmonates, salicylic acid, and brassinosteroids were differentially expressed. In addition, the majority of transcriptionally activated genes involved in hormone signaling (except for ethylene and salicylic acid signaling) were downregulated in abscised fruitlets. The differential expression of transcripts coding for enzymes involved in sucrose, glucose, trehalose, starch, galactose, and galactinol metabolism shows that sucrose, galactinol, and glucose synthesis and starch content were reduced as starch biosynthesis was blocked, and retrogradation and degradation intensified. These results suggest that the abscised pecan fruitlets stopped growing and developing for some time before dropping, further indicating that their sugar supply was reduced or stopped. The transcriptome characterization described in this paper contributes to unravelling the molecular mechanisms and pathways involved in the physiological abscission of pecan fruits.

PaPYL9 is involved in the regulation of apricot fruit ripening through ABA signaling pathway

Abscisic acid (ABA) is a major regulator of non-climacteric fruit ripening; however, the role of ABA in the ripening of climacteric fruit is not clear. Here, as a typical climacteric fruit, apricots were used to investigate the role of ABA in fruit ripening. Based on weighted gene co-expression network analysis (WGCNA) of our previous transcriptome data, we treated ‘Danxing’ fruit with exogenous ABA and obtained ABA receptor genes, genes related to ABA biosynthesis and signal transduction, and analyzed the response of these candidate genes to exogenous ABA during fruit ripening. Subsequently, the full length of candidate PYLs genes were cloned, and their putative function were analyzed by phylogenetic analysis and protein structure domain analysis. And then the function of one candidate gene PaPYL9 was verified by using transgenic tomato. Furthermore, the response genes in transgenic tomato were screened by transcriptome sequencing, and ultimately the related regulatory network was proposed. The results showed that the injection of exogenous 1.89 mmol·L-1 ABA remarkably promoted fruit coloration, and increased the color index for red grapes (CIRG) and the total soluble solids (TSS) content, but significantly decreased the firmness and titratable acid (TA) content (p < 0.01). Nordihydroguaiaretic acid (NDGA), the inhibitor of ABA, appeared to have the converse role in TA, TSS, CIRG and firmness, during the ripening process. One NCED (9-cis-epoxycarotenoiddioxygenase) and five ABA receptor genes related to signal transduction were mined from the transcriptome data of apricot fruit through WGCNA. Compared with the control, the expression levels of NCED1, PYL9 (PYR/PYL/RCAR), SnRK2 (SUCROSE NON-FERMENTING1 (SNF1)-RELATED PROTEIN KINASE 2S), and ABF2 (ABRE-binding bZIP transcription) were induced dramatically by ABA treatment (p < 0.01), while NDGA treatment significantly inhibited their expression. Based on gene expression and protein domain analysis, we inferred that PaPYL9 is putatively involved in apricot fruit ripening. Overexpression of PaPYL9 in Micro-TOM tomatoes resulted in the promotion of early ripening. Simultaneously, the expression levels of genes related ethylene biosynthesis, chlorophyll degradation, fruit softening, flavor formation, pigment synthesis, and metabolism were all significantly induced in overexpression of PaPYL9 tomatoes. This indicates the central role of ABA in climacteric fruit ripening. A regulatory network was tentatively proposed, laying the foundation to unveil the molecular mechanism of the regulatory role of PaPYL9 in fruit ripening.

Genome-wide Identification and Evolution of the PP2C Gene Family in Eight Rosaceae Species and Expression Analysis Under Stress in Pyrus bretschneideri.

Type 2C protein phosphatase (PP2C) plays an essential role in abscisic acid (ABA) signaling transduction processes. In the current study, we identify 719 putative PP2C genes in eight Rosaceae species, including 118 in Chinese white pear, 110 in European pear, 73 in Japanese apricot, 128 in apple, 74 in peach, 65 in strawberry, 78 in sweet cherry, and 73 in black raspberry. Further, the phylogenetic analysis categorized PbrPP2C genes of Chinese white pear into twelve subgroups based on the phylogenic analysis. We observed that whole-genome duplication (WGD) and dispersed gene duplication (DSD) have expanded the Rosaceae PP2C family despite simultaneous purifying selection. Expression analysis finds that PbrPP2C genes have organ-specific functions. QRT-PCR validation of nine PbrPP2C genes of subgroup A indicates a role in ABA-mediated response to abiotic stress. Finally, we find that five PbrPP2C genes of subgroup A function in the nucleus. In summary, our research suggests that the PP2C family functions to modulate ABA signals and responds to abiotic stress.

Roles of Glutathione in Mediating Abscisic Acid Signaling and Its Regulation of Seed Dormancy and Drought Tolerance.

Plant growth and development and interactions with the environment are regulated by phytohormones and other signaling molecules. During their evolution, plants have developed strategies for efficient signal perception and for the activation of signal transduction cascades to maintain proper growth and development, in particular under adverse environmental conditions. Abscisic acid (ABA) is one of the phytohormones known to regulate plant developmental events and tolerance to environmental stresses. The role of ABA is mediated by both its accumulated level, which is regulated by its biosynthesis and catabolism, and signaling, all of which are influenced by complex regulatory mechanisms. Under stress conditions, plants employ enzymatic and non-enzymatic antioxidant strategies to scavenge excess reactive oxygen species (ROS) and mitigate the negative effects of oxidative stress. Glutathione (GSH) is one of the main antioxidant molecules playing a critical role in plant survival under stress conditions through the detoxification of excess ROS, maintaining cellular redox homeostasis and regulating protein functions. GSH has recently emerged as an important signaling molecule regulating ABA signal transduction and associated developmental events, and response to stressors. This review highlights the current knowledge on the interplay between ABA and GSH in regulating seed dormancy, germination, stomatal closure and tolerance to drought.

The involvement of abscisic acid in hydrogen gas-enhanced drought resistance in tomato seedlings

Hydrogen gas (H2) regulates plant responses to abiotic and biotic stresses. Abscisic acid (ABA) might alleviate the adverse effects of drought stress. However, the mechanisms by which ABA and H2 ameliorate plant drought stress are unclear. Here, tomato “Micro-Tom” seedlings were used to investigate the interaction between H2 and ABA under drought conditions. The results showed that both hydrogen-rich water (HRW) and ABA increased plant height, stem diameter and root activity of tomato seedlings under drought stress, with optimal concentrations of 75% and 150 μM, respectively. HRW or ABA treatment was able to enhance drought tolerance by increasing photosynthesis, antioxidant enzyme activity and gene expression of antioxidant enzymes under drought stress. Fluridone (FLU), a synthetic inhibitor of ABA, significantly diminished the positive effects of HRW on plant height, stem diameter and root activity under drought stress, suggesting that ABA might play a crucial role in H2-enhanced drought resistance in tomato seedlings. The results revealed that the ABA content in the PEG + HRW treatment was 18% higher than that in the polyethylene glycol (PEG) treatment alone. Furthermore, we found that H2 enhanced endogenous ABA content by increasing zeaxanthin epoxidase (ZEP), 9-cis-epoxycarotenoid dioxygenase (NCED) and abscisic aldehyde oxidase (AAO) activities and the expression of SlZEP, SlNCED, and SlAAO. PEG + HRW treatment increased ZEP and NCED activities, which were 13% and 40% higher than those of PEG treatment, respectively. Meanwhile, the transcription levels of SlSnRK2 and SlAREB were upregulated by HRW or ABA under drought stress, whereas this upregulation was reversed by FLU. Thus, our results demonstrate that H2 was able to enhance drought resistance by regulating ABA biosynthesis and the expression of ABA signal transduction genes in tomato seedlings.

Genome-wide identification of ABA receptor PYL/RCAR gene family and their response to cold stress in Medicago sativa L.

The online version contains supplementary material available at 10.1007/s12298-021-01066-3.

Citrus transcription factor CsHB5 regulates abscisic acid biosynthetic genes and promotes senescence

Senescence is a gradual physiological process involving the integration of numerous internal and environmental signals. Abscisic acid (ABA) is a well-known inducer of senescence. However, the regulatory mechanisms underlying ABA-mediated senescence remain largely unknown. Here, we report that the citrus homeodomain leucine zipperI (HD-ZIPI) transcription factor CsHB5 functions as a regulator of ABA-triggered senescence. CsHB5 acts as a nucleus-localized transcriptional activator, the expression of which appeared to be closely associated with citrus senescence. Overexpression of CsHB5 in citrus calli upregulated the expression of ABA- and reactive oxygen species (ROS)-related genes, and significantly increased the content of ABA and hydrogen peroxide (H2 O2 ), whereas silencing CsHB5 in citrus calli downregulated the expression of ABA-related genes. Additionally, heterogenous overexpression of CsHB5 in Solanum lycopersicum (tomato) and Arabidopsis thaliana (Arabidopsis) leads to early leaf yellowing under dark-induced senescence conditions. Meanwhile, the levels of ABA and H2 O2 in transgenic tomatoes increased significantly and the lycopene content decreased. Transcriptome analysis of CsHB5-overexpressing citrus calli and tomato showed that CsHB5 was involved in multiple senescence-associated processes, including chlorophyll degradation, nutrient compound biosynthesis and transport, as well as ABA and ROS signal transduction. The results of yeast one-hybrid assays, electrophoretic mobility shift assays and dual luciferase assays indicated that CsHB5 directly binds to the promoters of ABA biosynthetic genes, including β-carotene hydroxylase1 (BCH1) and 9-cis-epoxycarotenoid dioxygenase2 (NCED2), thereby activating their transcription. Our findings revealed that CsHB5 participates in senescence, at least partly, by directly controlling ABA accumulation. Our work provides insight into the regulatory mechanisms underlying ABA-mediated senescence.

Hybridization With an Invasive Plant of Xanthium strumarium Improves the Tolerance of Its Native Congener X. sibiricum to Cadmium.

Hybridization is one of the important factors influencing the adaptive evolution of invasive plants. According to previous studies, hybridization with an invasive plant reduces the adaptability of its native congener to environment. However, in this study, the hybridization with an invasive plant of Xanthium strumarium (LT) improves the tolerance and accumulation of its native congener Xanthium sibiricum (CR) to cadmium (Cd). Under Cd stress, X. sibiricum♀ × X. strumarium♂ (ZCR) showed higher biomass and Cd accumulation. Compared with CR, ZCR has longer vegetative and reproductive growth time. Moreover, ZCR adopted more reasonable biomass allocation strategy. ZCR increased the proportion of reproductive allocation and ensured its own survival with the increase of Cd stress. Furthermore, ZCR increased the translocation of Cd to aboveground parts and changed the distribution of Cd. A large amount of Cd is stored in senescent leaves and eliminated from the plant when the leaves fall off, which not only reduces the Cd content in the plant, but also reduces the toxicity of Cd in the normal leaves. Transcriptome analysis shows a total of 2055 (1060 up and 995 down) differentially expressed genes (DEGs) were detected in the leaves of Cd-stressed ZCR compared with CR, while only 792 (521 up and 271 down) were detected in X. strumarium♀ × X. sibiricum♂ (ZLT) compared with LT. A large number of DGEs in ZCR and ZLT are involved in abscisic acid (ABA) synthesis and signal transduction. The genes induced by ABA in ZCR, including CNGC5/20, CPK1/28, CML, PTI1-like tyrosine-protein kinase 3, respiratory burst oxidase homolog protein C, and WRKY transcription factor 33 were found differentially expressed compared CR. carotenoid cleavage dioxygenase 4, NCED1/2, phytoene synthase 2, and CYP707A involved in ABA synthesis and decomposition in ZLT were found differentially expressed compared LT. We speculated that ABA played an important role in Cd transportation of hybrids and Cd distribution in senescent and normal leaves. The results demonstrate that hybridization with an invasive plant improves the adaptability of the hybrid to Cd stress and may enhance the extinction risk of native congener in pollution environment.

Integrative Identification of Crucial Genes Associated With Plant Hormone-Mediated Bud Dormancy in Prunus mume.

Prunus mume is an important ornamental woody plant with winter-flowering property, which is closely related to bud dormancy. Despite recent scientific headway in deciphering the mechanism of bud dormancy in P. mume, the overall picture of gene co-expression regulating P. mume bud dormancy is still unclear. Here a total of 23 modules were screened by weighted gene co-expression network analysis (WGCNA), of which 12 modules were significantly associated with heteroauxin, abscisic acid (ABA), and gibberellin (GA), including GA1, GA3, and GA4. The yellow module, which was positively correlated with the content of ABA and negatively correlated with the content of GA, was composed of 1,426 genes, among which 156 transcription factors (TFs) were annotated with transcriptional regulation function. An enrichment analysis revealed that these genes are related to the dormancy process and plant hormone signal transduction. Interestingly, the expression trends of PmABF2 and PmABF4 genes, the core members of ABA signal transduction, were positively correlated with P. mume bud dormancy. Additionally, the PmSVP gene had attracted lots of attention because of its co-expression, function enrichment, and expression level. PmABF2, PmABF4, and PmSVP were the genes with a high degree of expression in the co-expression network, which was upregulated by ABA treatment. Our results provide insights into the underlying molecular mechanism of plant hormone-regulated dormancy and screen the hub genes involved in bud dormancy in P. mume.

AsTal1 from Aquilaria sinensis regulates ABA signaling-mediated seed germination and root growth in Nicotiana benthamiana

Transaldolase, the key enzyme of the pentose-phosphate pathway, plays an important role in plant growth and defense. Seed germination is a key factor that influences the cultivation of Aquilaria sinensis, the plant source of agarwood, which is widely used as a traditional medicine, perfume and incenses. However, little is known about the function of transaldolase in abscisic acid (ABA) signaling-mediated seed germination. In the present study, the full-length AsTal1 gene was isolated and characterized from A. sinensis calli. Sublocalization analysis indicated that AsTal1 was localized in the chloroplast. In addition, phenotypic analysis indicated that AsTal1-overexpressing Nicotiana benthamiana (OE) plants were less sensitive to ABA during seed germination and root growth than wild-type (WT) plants. Overexpression of AsTal1 regulated the expression of genes involved in ABA metabolism, biosynthesis and signal transduction under ABA treatment. In addition, expression of NbRbohA and NbRbohB was inhibited in the overexpression lines, whereas the abundance and activities of the antioxidative enzymes were higher in the transgenic plants than in the WT lines after ABA treatment. Taken together, our results indicated that AsTal1 regulates ABA signaling-mediated seed germination and root growth by regulating the expression of genes involved in the ABA signaling pathway and the enzymes responsive to ROS.

Plant Hormones and Volatiles Response to Temperature Stress in Sweet Corn (Zea mays L.) Seedlings.

This work aims to emphasize on disclosing the regulative mechanism of sweet corn seedlings response to extreme temperature stress; transcriptomics and metabolomics for volatiles and plant hormones were integrated in this study. Results showed that low-temperature stress significantly impressed 20 volatiles; abscisic acid and salicylic acid accumulated, while auxin and jasmonic acid decreased. The regulatory patterns of vp14 and ABF for abscisic acid accumulation and signal transduction were elucidated in low-temperature stress. High-temperature stress influenced 31 volatiles and caused the reductions on zeatin, salicylic acid, jasmonic acid, and auxin. The up-regulation of an ARR-B gene emphasized its function on zeatin signal transduction under high-temperature stress. Correlations among gene modules, phytohormones, and volatiles were analyzed for building the regulative network of sweet corn seedlings under temperature stress. The attained result might build foundations for improving early development of sweet corn by biological intervention or genomic-level modulation.

The Halophyte Halostachys caspica AP2/ERF Transcription Factor HcTOE3 Positively Regulates Freezing Tolerance in Arabidopsis.

The APETALA2 (AP2) and ethylene-responsive element-binding factor (ERF) gene family is one of the largest plant-specific transcription factor gene families, which plays a critical role in plant development and evolution, as well as response to various stresses. The TARGET OF EAT3 (TOE3) gene is derived from Halostachys caspica and belongs to the AP2 subfamily with two AP2 DNA-binding domains. Currently, AP2 family mainly plays crucial roles in plant growth and evolution, yet there are few reports about the role of AP2 in abiotic stress tolerance. Here, we report HcTOE3, a new cold-regulated transcription factor gene, which has an important contribution to freezing tolerance. The main results showed that the expression of HcTOE3 in the H. caspica assimilating branches was strongly induced by different abiotic stresses, including high salinity, drought, and extreme temperature (heat, chilling, and freezing), as well as abscisic acid and methyl viologen treatments. Overexpressing HcTOE3 gene (OE) induced transgenic Arabidopsis plant tolerance to freezing stress. Under freezing treatment, the OE lines showed lower content of malondialdehyde and electrolyte leakage and less accumulation of reactive oxygen species compared with the wild type. However, the survival rates, antioxidant enzyme activities, and contents of osmotic adjustment substance proline were enhanced in transgenic plants. Additionally, the OE lines increased freezing tolerance by up-regulating the transcription level of cold responsive genes (CBF1, CBF2, COR15, COR47, KIN1, and RD29A) and abscisic acid signal transduction pathway genes (ABI1, ABI2, ABI5, and RAB18). Our results suggested that HcTOE3 positively regulated freezing stress and has a great potential as a candidate gene to improve plant freezing tolerance.

Transcriptome and proteome analyses of the molecular mechanisms underlying changes in oil storage under drought stress in Brassica napus L.

AbstractRapeseed (Brassica napus L.) is the second most important oilseed crop in edible vegetable oil and bioenergy; however, drought stress generally causes a decrease in rapeseed yield and oil content, especially during the reproductive stage. In our study, we measured the oil and protein contents and gibberellic acid (GA) and abscisic acid (ABA) levels in seeds that were acquired on the 30th, 40th, and 50th days after flowering under control and drought treatments. RNA and protein libraries were constructed from the stressed seeds to perform transcriptome and proteome analyses, respectively. Our results demonstrated that the oil content decreased due to four primary mechanisms: downregulation of fatty acid biosynthesis‐associated genes and proteins; upregulation of fatty acid degradation‐associated genes and proteins; enhancement of protein storage due to changes in the abundances of relevant genes and proteins; and upregulation of Gly‐Asp‐Ser‐Leu (GDSL) gene expression, potentially as the result of upregulating the GA biosynthesis gene GA20ox3 and downregulating the GA inactivating gene GA2ox3 and thus an increase in GA content. During seed maturation, oil storage change may also relate to increasing ABA content as the upregulation of two members of NCED6 (9‐cis‐epoxycarotenoid dioxygenase) gene family involved in ABA biosynthesis, and the upregulation of genes involved in ABA signal transduction. These results will help to establish a foundation for breeding excellent varieties of rapeseed with high oil content for areas with frequent droughts to promote the supply of edible vegetable oil and biofuel.

Wheat TaPUB1 protein mediates ABA response and seed development through ubiquitination

Abscisic acid (ABA) is an important regulator of plant growth, development, and biotic and abiotic stress responses. Ubiquitination plays important roles in regulating ABA signaling. E3 ligase, a key member in ubiquitination, actively participates in the regulation of biosynthesis, de-repression, and activation of ABA response and degradation of signaling components. In this study, we found that that overexpression of wheat E3 ligase TaPUB1 decreased the sensitivity of wheat seedlings to ABA, whereas TaPUB1-RNA interference (TaPUB1-RNAi) lines increased wheat sensitivity to ABA during germination, root growth, and stomatal opening. TaPUB1 influenced the expression of several ABA-responsive genes, and also interacted with TaPYL4 and TaABI5, which are involved in ABA signal transduction, and promoted their degradation. Additionally, we observed that TaPUB1-OE lines resulted in lower single-split grain numbers, larger seed size, and higher thousand kernel weight, when compared with the WT lines. Contrasting results were obtained for TaPUB1-RNAi lines. It suggests that TaPUB1 acts as a negative regulator in the ABA signaling pathway by interacting with TaPYL4 and TaABI5, subsequently affecting seed development in wheat. In addition, the enhanced abiotic tolerance of overexpression lines due to enhanced photosynthesis and root development may be related to the degradation of TaABI5 by TaPUB1.

OsbZIP72 Is Involved in Transcriptional Gene-Regulation Pathway of Abscisic Acid Signal Transduction by Activating Rice High-Affinity Potassium Transporter OsHKT1;1

We created CRISPR-Cas9 knock-out and overexpressing OsbZIP72 transgenic rice plants to gain a better understanding of the role and molecular mechanism of OsbZIP72 gene in stress tolerance, which has remained largely elusive. OsbZIP72 was expressed and integrated into rice transgenic plant genomes, and the OsbZIP72 transcript in overexpression lines was elicited by salinity, abscisic acid (ABA) and drought stresses. OsbZIP72 overexpressing plants showed higher tolerance to drought and salinity stresses, while knock-out transgenic lines showed higher sensitivity to these stresses. The differentially expressed genes (DEGs) from RNA-sequencing data encompassed several abiotic stress genes, and the functional classification of these DEGs demonstrated the robust transcriptome diversity in OsbZIP72. Yeast one-hybrid, along with luciferase assay, indicated that OsbZIP72 acted as a transcriptional initiator. Remarkably, electrophoresis mobility assay revealed that OsbZIP72 bound directly to the ABA- responsive element in the OsHKT1;1 promoter region and activated its transcription. Overall, our findings revealed that OsbZIP72 can act as a transcriptional modulator with the ability to induce the expression of OsHKT1;1 in response to environmental stress through an ABA-dependent regulatory pathway, indicating that OsbZIP72 can play a crucial role in the ABA-mediated salt and drought tolerance pathway in rice.

Mitogen-Activated Protein Kinase CaDIMK1 Functions as a Positive Regulator of Drought Stress Response and Abscisic Acid Signaling in Capsicum annuum.

Protein phosphorylation by kinase is an important mechanism for adapting to drought stress conditions. Here, we isolated the CaDIMK1 (Capsicum annuum drought-induced MAP kinase 1) from dehydrated pepper leaf tissue and functionally characterized it. Subcellular localization analysis revealed that the CaDIMK1 protein was localized in the cytoplasm and nucleus. CaDIMK1-silenced pepper plants exhibited drought-susceptible phenotypes that were characterized by increased transpiration rates, low leaf temperatures, and decreased stomatal closure. In contrast, CaDIMK1-overexpressing (OX) transgenic Arabidopsis plants were hypersensitive to abscisic acid (ABA) from germination to adult growth stages. Furthermore, the CaDIMK1-OX plants were tolerant to drought stress. The transcript levels of several stress-related genes were high in CaDIMK1-OX plants than in wild-type plants. Taken together, our data demonstrate that CaDIMK1 acts as a positive modulator of drought tolerance and ABA signal transduction in pepper plants.