ABA-dependent Signaling Pathway Research Articles

Genome-Wide Identification and Transcriptional Analysis of AP2/ERF Gene Family in Pearl Millet (Pennisetum glaucum).

The apetala2/ethylene response factor (AP2/ERF) gene family plays a crucial role in regulating plant growth and development and responding to different abiotic stresses (e.g., drought, heat, cold, and salinity). However, the knowledge of the ERF family in pearl millet remains limited. Here, a total of 167 high-confidence PgERF genes are identified and divided into five subgroups based on gene-conserved structure and phylogenetic analysis. Forty-one pairs of segmental duplication are found using collinear analysis. Nucleotide substitution analysis reveals these duplicated pairs are under positive purification, indicating they are actively responding to natural selection. Comprehensive transcriptomic analysis reveals that PgERF genesare preferentially expressed in the imbibed seeds and stem (tilling stage) and respond to heat, drought, and salt stress. Prediction of the cis-regulatory element by the PlantCARE program indicates that PgERF genes are involved in responses to environmental stimuli. Using reverse transcription quantitative real-time PCR (RT-qPCR), expression profiles of eleven selected PgERF genes are monitored in various tissues and during different abiotic stresses. Transcript levels of each PgERF gene exhibit significant changes during stress treatments. Notably, the PgERF7 gene is the only candidate that can be induced by all adverse conditions. Furthermore, four PgERF genes (i.e., PgERF22, PgERF37, PgERF88, and PgERF155) are shown to be involved in the ABA-dependent signaling pathway. These results provide useful bioinformatic and transcriptional information for understanding the roles of the pearl millet ERF gene family in adaptation to climate change.

Walnut phosphatase 2A proteins interact with basic leucine zipper protein JrVIP1 to regulate osmotic stress response via calcium signaling.

Walnut is an important economic tree species that is susceptible to osmotic stress. Scientific cultivation management is an important way to improve the yield and quality of walnuts, which requires understanding the regulatory mechanisms in response to osmotic stress. Therefore, in this study, 15 protein phosphatase 2A (PP2A) genes were identified from the walnut transcriptome (named JrPP2A01~15) and their potential function responses to osmotic stress were elucidated. The open reading frame (ORF) of JrPP2A01~15 ranges from 651 to 1,764 bp in length, the molecular weight of the encoded proteins are 24.15-65.61 kDa, and the theoretical isoelectric points are 4.80-8.37. These JrPP2As were unevenly distributed on 10 chromosomes and divided into five groups based on the composition of conserved domains, motifs, and exon/intron organizations. The five groups are JrPP2AAs, JrPP2AB's, JrPP2AB''s, JrPP2AB55s, and JrPP2ACs, including 1, 5, 2, 3, and 4 members, accordingly. The cis-elements in JrPP2As' promoters were involved in responses to hormone and abiotic stress. Most JrPP2A genes, excluding JrPP2A01, JrPP2A02, JrPP2A05, JrPP2A06, and JrPP2A13, could be induced significantly by PEG6000, NaCl, CaCl2 and ABA. JrPP2A02, JrPP2A05, JrPP2A07, JrPP2A09, and JrPP2A14, could independently interact with a bZIP transcription factor JrVIP1. Moreover, overexpression of JrPP2A07, JrPP2A09, and JrPP2A14 could significantly decrease ROS accumulation while increasing calcium (Ca) uptake exposed to PEG6000 and NaCl stresses, which was mediated by exogenous CaCl2 and ABA. These results suggested that JrPP2A genes play potential key roles in walnut response to drought and salt-inducing osmotic stress involving Ca- and ABA-dependent signaling pathways.

Transcriptomic analysis reveals the gene regulatory networks involved in leaf and root response to osmotic stress in tomato.

Tomato (Solanum lycopersicum L.) is a major horticultural crop that is cultivated worldwide and is characteristic of the Mediterranean agricultural system. It represents a key component of the diet of billion people and an important source of vitamins and carotenoids. Tomato cultivation in open field often experiences drought episodes, leading to severe yield losses, since most modern cultivars are sensitive to water deficit. Water stress leads to changes in the expression of stress-responsive genes in different plant tissues, and transcriptomics can support the identification of genes and pathways regulating this response. Here, we performed a transcriptomic analysis of two tomato genotypes, M82 and Tondo, in response to a PEG-mediated osmotic treatment. The analysis was conducted separately on leaves and roots to characterize the specific response of these two organs. A total of 6,267 differentially expressed transcripts related to stress response was detected. The construction of gene co-expression networks defined the molecular pathways of the common and specific responses of leaf and root. The common response was characterized by ABA-dependent and ABA-independent signaling pathways, and by the interconnection between ABA and JA signaling. The root-specific response concerned genes involved in cell wall metabolism and remodeling, whereas the leaf-specific response was principally related to leaf senescence and ethylene signaling. The transcription factors representing the hubs of these regulatory networks were identified. Some of them have not yet been characterized and can represent novel candidates for tolerance. This work shed new light on the regulatory networks occurring in tomato leaf and root under osmotic stress and set the base for an in-depth characterization of novel stress-related genes that may represent potential candidates for improving tolerance to abiotic stress in tomato.

Arabidopsis SnRK2.3/SRK2I plays a positive role in seed germination under cold stress conditions

Abscisic acid (ABA) plays a negative role in seed germination by inducing and maintaining seed dormancy. As core components of ABA signaling, the three subclass III SnRK2 protein kinases SnRK2.2, SnRK2.3, and SnRK2.6 play essential roles in the regulation of seed dormancy, seed germination, and seedling growth. However, their precise role in seed germination under cold stress conditions remains unclear. In Arabidopsis seeds, SnRK2.2 and SnRK2.3 genes were highly abundant compared to SnRK2.6, and their expression levels significantly declined during seed germination at 4 °C. Among knockout mutants of these SnRK2s, only snrk2.3 seeds showed significantly delayed germination under cold stress conditions, compared to wild-type seeds. Although this phenotypic abnormality of snrk2.3 was different from those caused by mutations in other ABA core components, such as RCAR5/PYL11 and AIP1/HAI2, it was partially rescued by blocking ABA biosynthesis. When germinated snrk2.3 seeds were grown vertically at 4 °C, their root growth was also severely inhibited compared to that of wild-type plants. In contrast to snrk2.3, SnRK2.3-overexpressing plants exhibited enhanced seed germination under cold stress conditions, and this SnRK2.3-mediated regulation of seed germination was accompanied by altered expression of genes involved in the response to ABA and GA, as well as genes involved in ABA and GA biosynthesis/catabolism. Taken together, the results of our study suggest that SnRK2.3 acts as a positive regulator of seed germination under cold stress conditions, and that this role may be mediated through ABA-dependent signaling pathways.

Lipids: A Key Regulatory Hub in Plant Stress Adaptation

The plants exert rapid responses to environmental stresses to adapt with the stress. Plants respond in many ways to different abiotic and biotic stresses. The first cellular component to sense stress signals is cell membrane. Cell membrane is a biological membrane, and its main constituents are Lipids that can sense conditions outside the cell. Remodeling of cellular membrane lipids is one of the critical mechanisms in the plant cells to withstand stresses. Lipids play a critical role in triggering and regulating cellular hormonal signaling cascades. There is a close correlation between ABA-dependent signaling and lipid metabolic pathways to maintain the integrity and the viability of cellular membranes. Phosphatidic acid, lysophospholipid, inositol phosphate, fatty acid, oxylipins, diacylglycerol, and sphingolipid are considered as the signaling molecules. Lipids also act as a stress reliever to lower the negative effects of stress. This review highlights the key regulatory roles of lipids in plant adaptation against the environmental stresses.

MicroRNA162 regulates stomatal conductance in response to low night temperature stress via abscisic acid signaling pathway in tomato

MicroRNAs (miRNAs) mediate the degradation of target mRNA and inhibit mRNA translation to regulate gene expression at the transcriptional and post-transcriptional levels in response to environmental stress in plants. We characterized the post-transcriptional mechanism by deep sequencing small RNA (sRNA) to examine how miRNAs were involved in low night temperature (LNT) stress in tomato and whether the molecular mechanism depended on the abscisic acid (ABA) signaling pathway. We annotated conserved miRNAs and novel miRNAs with four sRNA libraries composed of wild-type (WT) tomato plants and ABA-deficient mutant (sit) plants under normal growth and LNT stress conditions. Reverse genetics analysis suggested that miR162 participated in LNT resistance and the ABA-dependent signaling pathway in tomato. miR162-overexpressing (pRI-miR162) and miR162-silenced (pRNAi-miR162) transgenic tomato plants were generated to evaluate miR162 functions in response to LNT stress. miR162 deficiency exhibited high photosynthetic capacity and regulated stomatal opening, suggesting negative regulation of miR162 in the ABA-dependent signaling pathway in response to LNT stress. As feedback regulation, miR162 positively regulated ABA to maintain homeostasis of tomato under diverse abiotic stresses. The mRNA of DICER-LIKE1 (DCL1) was targeted by miR162, and miR162 inhibited DCL1 cleavage in LNT response, including the regulation of miRNA160/164/171a and their targets. The DCL1-deficient mutants (dcl1) with CRISPR/Cas9 prevented stomatal opening to influence photosynthesis in the ABA signaling pathway under LNT stress. Finally, we established the regulatory mechanism of ABA-miR162-DCL1, which systematically mediated cold tolerance in tomato. This study suggests that post-transcriptional modulators acted as systemic signal responders via the stress hormone signaling pathway, and the model at the post-transcriptional level presents a new direction for research in plant abiotic stress resistance.

Genome-Wide Identification of 14-3-3 gene family reveals their diverse responses to abiotic stress by interacting with StABI5 in Potato (Solanum tuberosum L.).

The 14-3-3 genes are widely present in plants and participate in a wide range of cellular and physiological processes. In the current study, twelve 14-3-3s were identified from potato genome. According to phylogenetic evolutionary analysis, potato 14-3-3s were divided into ϵ and non-ϵ groups. Conserved motif and gene structure analysis displayed a distinct class-specific divergence between the ϵ group and non-ϵ group. Multiple sequence alignments and three-dimensional structure analysis of 14-3-3 proteins indicated all the members contained nine conservative antiparallel α-helices. The majority of 14-3-3s had transcript accumulation in each detected potato tissue, implying their regulatory roles across all stages of potato growth and development. Numerous cis-acting elements related to plant hormones and abiotic stress response were identified in the promoter region of potato 14-3-3s, and the transcription levels of these genes fluctuated to different degrees under exogenous ABA, salt and drought stress, indicating that potato 14-3-3s may be involved in different hormone signaling pathways and abiotic stress responses. In addition, eight potato 14-3-3s were shown to interact with StABI5, which further demonstrated that potato 14-3-3s were involved in the ABA-dependent signaling pathway. This study provides a reference for the identification of the 14-3-3 gene family in other plants, and provides important clues for cloning potential candidates in response to abiotic stresses in potato.

PheLBD29, an LBD transcription factor from Moso bamboo, causes leaf curvature and enhances tolerance to drought stress in transgenic Arabidopsis

The lateral organ boundaries domain (LBD), a unique family of transcription factors in higher plants, plays a key role in plant growth and development, and stress response. Here, we report on the novel lateral organ boundaries domain (LBD) gene PheLBD29, a nuclear localization protein that can bind the conserved GCCCCG sequence, as determined by electrophoretic mobility shift assay (EMSA). PheLBD29 was highly expressed in blade leaf and significantly induced by polyethylene glycol (PEG). Overexpression of PheLBD29 leads to small and abaxially rolled leaves in Arabidopsis, and anatomically, 35S:PheLBD29 Arabidopsis leaves showed transformation of adaxial cells into abaxial cells. Moreover, overexpression of PheLBD29 in Arabidopsis increased plant tolerance to drought stress, by accumulation of more soluble sugars, less malondialdehyde (MDA), and had lower REL levels under drought stress. Transient expression assay revealed PheLBD29 directly bound to the promoter region of RAB18. In addition, 35S:PheLBD29 Arabidopsis showed higher sensitivity to abscisic acid (ABA) than the wild type. Therefore, we conclude that PheLBD29 may participate in the ABA-dependent signaling pathway to improve drought tolerance. Our study provides new evidence for a Moso bamboo LBD protein regulatory module in leaf curvature and drought resistance.

Genome-Wide Characterization and Expression Profiling of the GRAS Gene Family in Salt and Alkali Stresses in Miscanthus sinensis

The GRAS family genes encode plant-specific transcription factors that play important roles in a diverse range of developmental processes and abiotic stress responses. However, the information of GRAS gene family in the bioenergy crop Miscanthus has not been available. Here, we report the genome-wide identification of GRAS gene family in Micanthus sinensis. A total of 123 MsGRAS genes were identified, which were divided into ten subfamilies based on the phylogenetic analysis. The co-linearity analysis revealed that 59 MsGRAS genes experienced segmental duplication, forming 35 paralogous pairs. The expression of six MsGRAS genes in responding to salt, alkali, and mixed salt-alkali stresses was analyzed by transcriptome and real-time quantitative PCR (RT-qPCR) assays. Furthermore, the role of MsGRAS60 in salt and alkali stress response was characterized in transgenic Arabidopsis. The MsGRAS60 overexpression lines exhibited hyposensitivity to abscisic acid (ABA) treatment and resulted in compromised tolerance to salt and alkali stresses, suggesting that MsGRAS60 is a negative regulator of salt and alkali tolerance via an ABA-dependent signaling pathway. The salt and alkali stress-inducible MsGRAS genes identified serve as candidates for the improvement of abiotic stress tolerance in Miscanthus.

Overexpression of SmMYC2 enhances salt resistance in Arabidopsis thaliana and Salvia miltiorrhiza hairy roots

Soil salinity significantly affects both Salvia miltiorrhiza growth and development as well as seed germination throughout field cultivation and production. The basic helix-loop-helix (bHLH) transcription factor (TF) MYC2 contributes significantly to plant stress resistance as a key regulator of the jasmonic acid signaling pathway. In transgenic S. miltiorrhiza hairy roots, SmMYC2 has been shown to promote the accumulation of tanshinone and salvianolic acid, but its role in S. miltiorrhiza of resistance to abiotic stress is unclear. Herein, we found methyl jasmonate (MeJA), NaCl, and PEG treatment all significantly increased SmMYC2 expression. In response to salt stress, SmMYC2 overexpression in yeast increased its rate of growth. Additionally, overexpression of SmMYC2 transgenic Arabidopsis thaliana and S. miltiorrhiza hairy root showed that it might improve salt resistance in transgenic plant. In particular, compared to WT, overexpression of SmMYC2 transgenic Arabidopsis had higher levels of three antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), proline (Pro) content, and ABA-dependent and ABA-independent genes expression. They also had lower levels of malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation. What's more, overexpression of SmMYC2 increases the expression of flavonoid synthesis genes and the accumulation of related components in Arabidopsis. These findings imply that SmMYC2 functions as a positive regulator that regulates plant tolerance to salt through ABA-dependent and independent signaling pathways.

Heterologous Overexpression of ZmHDZIV13 Enhanced Drought and Salt Tolerance in Arabidopsis and Tobacco

The homeodomain leucine zipper (HD-Zip) IV transcription factor is indispensable in the response of plants to abiotic stress. Systematic studies have been carried out in Arabidopsis, rice and other species from which a series of stress resistance-related genes have been isolated. However, the function of the HD-Zip IV protein in maize is not clear. In this study, we cloned the HD-Zip IV gene ZmHDZIV13 and identified its function in the stress response. Our phylogenetic analysis showed that ZmHDZIV13 and AtHDG11 had high homology and might have similar functions. The heterologous overexpression of ZmHDZIV13 in Arabidopsis resulted in sensitivity to abscisic acid (ABA), salt tolerance during germination and drought tolerance in seedlings. Under drought stress, the transgenic Arabidopsis showed stronger drought resistance than the wild-type (control). The malondialdehyde content of ZmHDZIV13 transgenic plants was lower than that of the control, and the relative water content and proline content were significantly higher than those of the control. After the drought was relieved, the expression levels of stress-related genes were up-regulated in transgenic Arabidopsis. These results show that ZmHDZIV13, as a stress-responsive transcription factor, plays a role in the positive regulation of abiotic stress tolerance and can regulate an ABA-dependent signaling pathway to regulate drought response in plants.

Transcriptome-wide identification of walnut PP2C family genes in response to external stimulus

Walnut is an important economic tree species while confronting with global environmental stress, resulting in decline in quality and yield. Therefore, it is urgent to elucidate the molecular mechanism for the regulation of walnut response to adversity. The protein phosphatase 2C (PP2C) gene family participates in cellular processes in eukaryotes through reversible phosphorylation of proteins and signal transduction regulation. However, the stress response function of PP2C genes was far to be clarified. Therefore, to understand the stress response mechanism of walnut tree, in this study, a total of 41 PP2C genes with complete ORFs were identified from Juglans regia, whose basic bio-information and expression patterns in response to multiple stresses and ABA were confirmed. The results showed that the ORFs of JrPP2Cs were 495 ~ 3231 bp in length, the predicted JrPP2C proteins contained 164 to 1076 amino acids and the molecular weights were 18,581.96 ~ 118,853.34 Da, the pI was 4.55 ~ 9.58. These JrPP2C genes were unevenly distributed on 14 chromosomes, among which Chr11 and Chr13 contained the most genes. Phylogenetic analysis found that these JrPP2C proteins were classed into 9 subfamilies, among which group F covered most JrPP2Cs. The JrPP2Cs in the same subfamily exhibited similarities in the composition of conserved domains, amino acid sequences of motifs and exon/intron organization in DNA sequences. Each JrPP2C includes 4 ~ 10 motifs and each motif contained 15 ~ 37 amino acids. Among the motifs, motif1, motif2, motif3 and motif8 were most abundant. Most of the JrPP2C genes diversely response to osmotic, cadmium, and Colletotrichum gloeosporioide stress as well as ABA treatments, among which JrPP2C28, JrPP2C17, JrPP2C09, JrPP2C36 were more obvious and deserves further attention. All these results indicated that JrPP2C genes play potential vital roles in plant response to multiple stimulus, and are possibly involved in ABA-dependent signaling pathway.

Tartary buckwheat FtMYB30 transcription factor improves the salt/drought tolerance of transgenic Arabidopsis in an ABA-dependent manner.

Drought and high salinity affect plant growth, development, yield, and quality. MYB transcription factors (TFs) in plants play an indispensable regulatory role in resisting adverse stress. In this study, screening and functional validation of the TF FtMYB30, which can respond extensively to abiotic stress and abscisic acid (ABA), was achieved in Tartary buckwheat. FtMYB30, one of the SG22 (sub-group 22) family of R2R3-MYB TFs, localized in the nucleus and had transcriptional activation activity. Under drought and salt stress, FtMYB30 overexpression reduced the oxidative damage in transgenic plants by increasing the activity of proline content and antioxidant enzymes and significantly upregulate the expression of RD29A, RD29B, and Cu/ZnSOD, thereby enhancing drought/salt tolerance in transgenic Arabidopsis. Additionally, overexpression of FtMYB30 can reduce the sensitivity of transgenic plants to ABA. Moreover, AtRCAR1/2/3 and AtMPK6 directly interact with the FtMYB30 TF, possibly through the crosstalk between MAPKs (mitogen-activated protein kinases) and the ABA signaling pathway. Taken together, these results suggest that FtMYB30, as a positive regulator, mediates plant tolerance to salt and drought through an ABA-dependent signaling pathway.

SlSnRK2.3 interacts with SlSUI1 to modulate high temperature tolerance via Abscisic acid (ABA) controlling stomatal movement in tomato

Tomato is often exposed to high temperature stress during summer cultivation. Stomatal movement plays important roles in photosynthesis and transpiration which restricts the quality and yield of tomato under environmental stress. To elucidate the mechanism of stomatal movement in high temperature tolerance, SlSnRK2s (sucrose non-fermenting 1-related protein kinases) silenced plants were generated in tomato with CRISPR-Cas 9 gene editing techniques. Through the observation of stomatal parameters, SlSnRK2.3 regulated stomatal closure which was responded to ABA (abscisic acid) and activated signaling pathway of ROS (reactive oxygen species) in high temperature stress. Based on the positive functions of SlSnRK2.3, the cDNA library was generated to investigate interaction proteins of SlSnRK2s. The interaction between SlSnRK2.3 and SlSUI1 (protein translation factor SUI1 homolog) was employed by Yeast two hybrid assay (Y2H), Luciferase (LUC), and Bimolecular fluorescence complementation (BiFC). Finally, the specific interactive sites between SlSnRK2.3 and SlSUI1 were verified by site-directed mutagenesis. The consistent mechanism of SlSnRK2.3 and SlSUI1 in stomatal movement, indicating that SlSUI1 interacted with SlSnRK2.3 through ABA-dependent signaling pathway in high temperature stress. Our results provided evidence for improving the photosynthetic capacity of tomato under high temperature stress, and support the breeding and genetic engineering of tomato over summer facility cultivation.

Homologous Drought-Induced 19 Proteins, PtDi19-2 and PtDi19-7, Enhance Drought Tolerance in Transgenic Plants.

Drought-induced 19 (Di19) proteins play important roles in abiotic stress responses. Thus far, there are no reports about Di19 family in woody plants. Here, eight Di19 genes were identified in poplar. We analyzed phylogenetic tree, conserved protein domain, and gene structure of Di19 gene members in seven species. The results showed the Di19 gene family was very conservative in both dicotyledonous and monocotyledonous forms. On the basis of transcriptome data, the expression patterns of Di19s in poplar under abiotic stress and ABA treatment were further studied. Subsequently, homologous genes PtDi19-2 and PtDi19-7 with strong response to drought stress were identified. PtDi19-2 functions as a nuclear transcriptional activator with a transactivation domain at the C-terminus. PtDi19-7 is a nuclear and membrane localization protein. Additionally, PtDi19-2 and PtDi19-7 were able to interact with each other in yeast two-hybrid system. Overexpression of PtDi19-2 and PtDi19-7 in Arabidopsis was found. Phenotype identification and physiological parameter analysis showed that transgenic Arabidopsis increased ABA sensitivity and drought tolerance. PtDi19-7 was overexpressed in hybrid poplar 84K (Populus alba × Populus glandulosa). Under drought treatment, the phenotype and physiological parameters of transgenic poplar were consistent with those of transgenic Arabidopsis. In addition, exogenous ABA treatment induced lateral bud dormancy of transgenic poplar and stomatal closure of transgenic Arabidopsis. The expression of ABA/drought-related marker genes was upregulated under drought treatment. These results indicated that PtDi19-2 and PtDi19-7 might play a similar role in improving the drought tolerance of transgenic plants through ABA-dependent signaling pathways.

Identification and molecular analysis of the annexin genes in Cyamopsis tetragonoloba L

Annexins are a family of multigene proteins involved in plant development and stress responses. In the current study, the guar transcriptome database yielded a total of five annexin unigenes (named AnnCt1-AnnCt5). The predicted molecular weight of detected AnnCts was estimated to be between 35.22 and 37.03 kDa, with theoretical pIs ranging from 5.97 to 9.15. AnnCts have four annexin repeats that contain endonexin domains with Ca2+-binding sites with 24.44 to 71.74% of amino acid similarity among each other. The coding sequences (CDS) of two of the five guar annexins (AnnCt1 and AnnCt5) were completely cloned and were similar to the ones retrieved. AnnCts were divided into four groups based on their phylogenetic study, indicating evolutionary connections with higher plant annexins and a close relationship with Glycine max. Predominant expression of AnnCt1 followed by AnnCt2 and AnnCt5 were observed more in green organs such mature leaves, shoots, and developing seeds (30DAF) indicated their significant roles. AnnCts genes have respond to drought, salt, cold, and abscisic acid (ABA) treatments showing possible roles in ABA-dependent or independent stress signaling pathways. In-silico analysis of soybean annexin (evolutionary close to guar annexin) predicted interactions with proteins that are possibly involve in organogenesis, transportation, and transcription regulation. The purified rAnnCt1 protein has shown DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) radical scavenging activity in-vitro. Our findings show that AnnCts are often guar annexins, that may play critical roles in different guar organs as well as contribute to stress tolerance and, its purified rAnnCt1 protein has antioxidant activity.

TaFLZ2D enhances salinity stress tolerance via superior ability for ionic stress tolerance and ROS detoxification

Salinity stress severely affects plant growth and crop productivity. FCS-like zinc finger family genes (FLZ) play important roles in plant growth and stress responses. But most information of this family obtained was involved in sucrose signaling, limited function has been known in response to salinity stress. In this study, a novel FLZ gene TaFLZ2D has been isolated and characterized in response to salinity stress in wheat. TaFLZ2D was induced by both salinity stress and exogenous abscisic acid (ABA). Its transcript level was substantially higher in the salt resistant wheat cultivar SR3 than in its closely related but salt sensitive cultivar JN177. Transient expression in Nicotiana benthamiana leaf epidermal cells demonstrated TaFLZ2D was localized both in the cytoplasm membrane and nucleus. Constitutive expression of TaFLZ2D in Arabidopsis thaliana improved salinity stress tolerance and ABA sensitivity. Phenotype analysis under KCl and mannitol treatment demonstrated TaFLZ2D increased salinity stress tolerance mainly due to the superior ability to cope with ionic stress. TaFLZ2D over-expressing lines increased abscisic acid synthesis, peroxidase activity and reduced rate of water loss. Transcriptomic analysis demonstrated over-expression of TaFLZ2D regulated ABA-dependent and independent signaling pathway related genes expression and activated antioxidant related genes expression under normal condition and Ca2+ signaling related genes expression under NaCl treatmemt. Taken together, TaFLZ2D is a positive regulator of salinity stress tolerance, which contributes to salinity stress mainly through superior ability for ionic stress tolerance and ROS detoxification.

Maize ZmbZIP33 Is Involved in Drought Resistance and Recovery Ability Through an Abscisic Acid-Dependent Signaling Pathway.

Analyzing the transcriptome of maize leaves under drought stress and rewatering conditions revealed that transcription factors were involved in this process, among which ZmbZIP33 of the ABSCISIC ACID-INSENSITIVE 5-like protein 5 family was induced to significantly up-regulated. The functional mechanism of ZmbZIP33 in Abscisic acd (ABA) signaling pathway and its response to drought stress and rewatering has not been studied yet. The present study found that ZmbZIP33 contains a DNA-binding and dimerization domain, has transcriptional activation activity, and is highly homologous to SbABI1,SitbZIP68 and OsABA1. The expression of ZmbZIP33 is strongly up-regulated by drought, high salt, high temperature, and ABA treatments. Overexpression of ZmbZIP33 remarkably increased chlorophyll content and root length after drought stress and rewatering, and, moreover, cause an accumulation of ABA content, thereby improving drought resistance and recovery ability in Arabidopsis. However, silencing the expression of ZmbZIP33 (BMV-ZmbZIP33) remarkably decreased chlorophyll content, ABA content, superoxide dismutase and peroxidase activities, and increased stomatal opening and water loss rate compared with BMV (control). It showed that silencing ZmbZIP33 lead to reduced drought resistance and recovery ability of maize. ABA sensitivity analysis found that 0.5 and 1 μmol/L treatments severely inhibited the root development of overexpression ZmbZIP33 transgenic Arabidopsis. However, the root growth of BMV was greatly inhibited for 1 and 5μmol/L ABA treatments, but not for BMV-ZmbZIP33. Subcellular localization, yeast two-hybrid and BIFC further confirmed that the core components of ABA signaling pathways ZmPYL10 and ZmPP2C7 interacted in nucleus, ZmPP2C7 and ZmSRK2E as well as ZmSRK2E and ZmbZIP33 interacted in the plasma membrane. We also found that expression levels of ZmPYL10 and ZmSRK2E in the BMV-ZmbZIP33 mutant were lower than those of BMV, while ZmPP2C7 was the opposite under drought stress and rewatering. However, expression of ZmPYL10 and ZmSRK2E in normal maize leaves were significantly up-regulated by 3–4 folds after drought and ABA treatments for 24 h, while ZmPP2C7 was down-regulated. The NCED and ZEP encoding key enzymes in ABA biosynthesis are up-regulated in overexpression ZmbZIP33 transgenic line under drought stress and rewatering conditions, but down-regulated in BMV-ZmbZIP33 mutants. Together, these findings demonstrate that ZmbZIP33 played roles in ABA biosynthesis and regulation of drought response and rewatering in Arabidopsis and maize thought an ABA-dependent signaling pathway.

SUPEROXIDE DISMUTASE FAMILY GENES IN WATERMELON AND THEIR RESPONSES TO DIFFERENT ABIOTIC STRESSES

<List> <ListItem><ItemContent> • A total of 8 <i>SOD</i> genes from watermelon were identified and bioinformatically analyzed. </ItemContent></ListItem> <ListItem><ItemContent> • The SOD proteins from watermelon and other different plant species can be classified into five groups consistent with their metal cofactors. </ItemContent></ListItem> <ListItem><ItemContent> • <i>ClSOD</i> genes exhibited distinctive tissue-specific and abiotic stress responsive expression patterns. </ItemContent></ListItem></List> Superoxide dismutase (SOD) is an important enzyme in the antioxidant system of plants and plays a vital role in stress responses by maintaining the dynamic balance of reactive oxygen species (ROS) concentrations. Genome-wide analysis of the <i>SOD</i> gene family in various plant species has been conducted but little is known about this gene family in watermelon (<i>Citrullus lanatus</i>). Here, eight <i>SOD</i> genes were identified in the watermelon genome and are designated <i>ClCSD1-5</i>, <i>ClFSD1-2</i> and <i>ClMSD</i> according to their metal cofactors. Phylogenetic analysis shows that SOD proteins from various plant species can be classified into five groups and members in the same group possess the same metal cofactor and similar subcellular localizations. Expression analysis of the <i>ClSOD</i> genes indicates that they had tissue-specific expression patterns with high expression in different tissues including the leaves, flowers and fruit. In addition, the expression of <i>ClSOD</i> genes differed appreciably under salinity, drought and abscisic acid (ABA) treatments, indicating that they may be involved in ROS scavenging under different abiotic stresses via an ABA-dependent signaling pathway. These results lay the foundation for elucidating the function of <i>ClSOD</i> genes in stress tolerance and fruit development in watermelon.

OsPP2C09 Is a Bifunctional Regulator in Both ABA-Dependent and Independent Abiotic Stress Signaling Pathways.

Clade A Type 2C protein phosphatases (PP2CAs) negatively regulate abscisic acid (ABA) signaling and have diverse functions in plant development and in response to various stresses. In this study, we showed that overexpression of the rice ABA receptor OsPYL/RCAR3 reduces the growth retardation observed in plants exposed to osmotic stress. By contrast, overexpression of the OsPYL/RCAR3-interacting protein OsPP2C09 rendered plant growth more sensitive to osmotic stress. We tested whether OsPP2CAs activate an ABA-independent signaling cascade by transfecting rice protoplasts with luciferase reporters containing the drought-responsive element (DRE) or ABA-responsive element (ABRE). We observed that OsPP2CAs activated gene expression via the cis-acting drought-responsive element. In agreement with this observation, transcriptome analysis of plants overexpressing OsPP2C09 indicated that OsPP2C09 induces the expression of genes whose promoters contain DREs. Further analysis showed that OsPP2C09 interacts with DRE-binding (DREB) transcription factors and activates reporters containing DRE. We conclude that, through activating DRE-containing promoters, OsPP2C09 positively regulates the drought response regulon and activates an ABA-independent signaling pathway.