Identification of an important site for function of the type 2C protein phosphatase ABI2 in abscisic acid signalling in Arabidopsis

MePP2C24, a cassava (Manihot esculenta) gene encoding protein phosphatase 2C, negatively regulates drought stress and abscisic acid responses in transgenic Arabidopsis thaliana

Abscisic acid (ABA) signaling plays a crucial role in plant development and response to abiotic/biotic stress. However, the function and regulation of protein phosphatase 2C (PP2C), a key component of abscisic acid signaling, under abiotic stress are still unknown in cassava, a drought-tolerant crop. In this study, a cassava PP2C gene (MePP2C24) was cloned and characterized. The MePP2C24 transcripts increased in response to mannitol, NaCl, and ABA. Overexpression of MePP2C24 in Arabidopsis resulted in increased sensitivity to drought stress and decreased sensitivity to exogenous ABA. This was demonstrated by transgenic lines having higher levels of malondialdehyde (MDA), ion leakage (IL), and reactive oxygen species (ROS), lower activities of catalase (CAT) and peroxidase (POD), and lower proline content than wild type (WT) under drought stress. Moreover, MePP2C24 overexpression caused decrease in expression of drought-responsive genes related to ABA signaling pathway. In addition, MePP2C24 was localized in the cell nucleus and showed self-activation. Furthermore, many MePYLs (MePYL1, MePYL4, MePYL7-9, and MePYL11-13) could interact with MePP2C24 in the presence of ABA, and MePYL1 interacted with MePP2C24 in both the presence and absence of ABA. Additionally, MebZIP11 interacted with the promoter of MePP2C24 and exerted a suppressive effect. Taken together, our results suggest that MePP2C24 acts as a negative regulator of drought tolerance and ABA response.

Comprehensive analysis of transcriptional data on seed germination of two maize inbred lines under low-temperature conditions

Seed germination directly affect maize yield and grain quality. Low-temperature reduces maize yield by affecting seed germination and seedling growth. However, the molecular mechanism of maize seed germination under low-temperature remains unclear. In this study, the transcriptome data of two maize inbred lines SCL127 (chilling-sensitive) and SCL326 (chilling-tolerant) were analyzed at five time points (0 H, 4 H, 12 H, 24 H, and 48 H) under low-temperature conditions. Through the comparison of SCL127-0 H-vs-SCL326-0 H (Group I), SCL127-4 H-vs-SCL326-4 H (Group Ⅱ), SCL127-12 H-vs-SCL326-12 H (Group Ⅲ), SCL127-24 H-vs-SCL326-24 H (Group Ⅳ), and SCL127-48 H-vs SCL326-48 H (Group Ⅴ), a total of 8,526 differentially expressed genes (DEGs) were obtained. Weighted correlation network analysis revealed that Zm00001d010445 was the hub gene involved in seed germination under low-temperature conditions. Zm00001d010445-based association analysis showed that Hap Ⅱ (G) was the excellent haplotype for seed germination under low-temperature conditions. These findings provide a new perspective for the study of the genetic architecture of maize tolerance to low-temperature and contribute to the cultivation of maize varieties with low-temperature tolerance.

Comprehensive functional analysis of the PYL-PP2C-SnRK2s family in Bletilla striata reveals that BsPP2C22 and BsPP2C38 interact with BsPYLs and BsSnRK2s in response to multiple abiotic stresses

As the core regulation network for the abscisic acid (ABA) signaling pathway, the PYL-PP2C-SnRK2s family commonly exists in many species. For this study, a total of 9 BsPYLs, 66 BsPP2Cs, and 7 BsSnRK2s genes were identified based on the genomic databases of Bletilla striata, which were classified into 3, 10, and 3 subgroups, respectively. Basic bioinformatics analysis completed, including the physicochemical properties of proteins, gene structures, protein motifs and conserved domains. Multiple cis-acting elements related to stress responses and plant growth were found in promoter regions. Further, 73 genes were localized on 16 pseudochromosomes and 29 pairs of paralogous genes were found via intraspecific collinearity analysis. Furthermore, tissue-specific expression was found in different tissues and germination stages. There were two BsPYLs, 10 BsPP2Cs, and four BsSnRK2 genes that exhibited a difference in response to multiple abiotic stresses. Moreover, subcellular localization analysis revealed six important proteins BsPP2C22, BsPP2C38, BsPP2C64, BsPYL2, BsPYL8, and BsSnRK2.4 which were localized in the nucleus and plasma membrane. Finally, yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays suggested that BsPP2C22 and BsPP2C38 could interact with multiple BsPYLs and BsSnRK2s proteins. This study systematically reported on the identification and characterization of the PYL-PP2C-SnRK2s family in B. striata, which provided a conceptual basis for deep insights into the functionality of ABA core signal pathways in Orchidaceae.

Hydrogen sulphide signalling in plant response to abiotic stress

Throughout their whole life cycle, higher plants are often exposed to diverse environmental stresses, such as drought, salinity, heavy metals and extreme temperatures. In response to such stress, plant cells initiate signalling transduction, resulting in downstream responses, such as specific gene transcription and protein expression. Accumulating evidence has revealed that hydrogen sulphide (H₂ S) serves as a signalling molecule in plant acclimation to stressful conditions. More important, H₂ S interacts with other signalling molecules and phytohormones, contributing to transcriptional regulation and post-translational modification. Overall, the H₂ S-mediated signalling pathway and its interaction with other signals remains elusive. Here, we describe the role of the H₂ S signalling network in regulating physiological and molecular processes under various abiotic stresses.

Genome-Wide Analysis of the Protein Phosphatase 2C Genes in Tomato

The plant protein phosphatase 2C (PP2C) plays an irreplaceable role in phytohormone signaling, developmental processes, and manifold stresses. However, information about the PP2C gene family in tomato (Solanum lycopersicum) is relatively restricted. In this study, a genome-wide investigation of the SlPP2C gene family was performed. A total of 92 SlPP2C genes were identified, they were distributed on 11 chromosomes, and all the SlPP2C proteins have the type 2C phosphatase domains. Based on phylogenetic analysis of PP2C genes in Arabidopsis, rice, and tomato, SlPP2C genes were divided into eight groups, designated A–H, which is also supported by the analyses of gene structures and protein motifs. Gene duplication analysis revealed that the duplication of whole genome and chromosome segments was the main cause of SLPP2Cs expansion. A total of 26 cis-elements related to stress, hormones, and development were identified in the 3 kb upstream region of these SlPP2C genes. Expression profile analysis revealed that the SlPP2C genes display diverse expression patterns in various tomato tissues. Furthermore, we investigated the expression patterns of SlPP2C genes in response to Ralstonia solanacearum infection. RNA-seq and qRT-PCR data reveal that nine SlPP2Cs are correlated with R. solanacearum. The above evidence hinted that SlPP2C genes play multiple roles in tomato and may contribute to tomato resistance to bacterial wilt. This study obtained here will give an impetus to the understanding of the potential function of SlPP2Cs and lay a solid foundation for tomato breeding and transgenic resistance to plant pathogens.

Populus euphratica Apyrases Increase Drought Tolerance by Modulating Stomatal Aperture in Arabidopsis

Stomatal regulation is crucial to reduce water consumption under drought conditions. Extracellular ATP (eATP) serves as a signaling agent in stomatal regulation; however, it is less known whether the eATP mediation of stomatal aperture is linked to apyrases (APYs), the principal enzymes that control the concentration of eATP. To clarify the role of APYs in stomatal control, PeAPY1 and PeAPY2 were isolated from Populus euphratica and transferred into Arabidopsis. Compared with the wild-type Arabidopsis and loss-of-function mutants (Atapy1 and Atapy2), PeAPY1- and PeAPY2-transgenic plants decreased stomatal aperture under mannitol treatment (200 mM, 2 h) and reduced water loss during air exposure (90 min). The role of apyrase in stomatal regulation resulted from its control in eATP-regulated stomatal movements and increased stomatal sensitivity to ABA. The bi-phasic dose-responses to applied nucleotides, i.e., the low ATP (0.3-1.0 mM)-promoted opening and high ATP (>2.0 mM)-promoted closure, were both restricted by P. euphratica apyrases. It is noteworthy that eATP at a low concentration (0.3 mM) counteracted ABA action in the regulation of stomatal aperture, while overexpression of PeAPY1 or PeAPY2 effectively diminished eATP promotion in opening, and consequently enhanced ABA action in closure. We postulate a speculative model of apyrase signaling in eATP- and ABA-regulated stomatal movements under drought.

Genome-wide analysis of PYL-PP2C-SnRK2s family in Camellia sinensis

Abscisic acid (ABA) signaling regulates plant growth and development and participates in response to abiotic stressors. However, details about the PYL-PP2C-SnRK2 gene family, which is the core component of ABA signaling in Camellia sinensis, are unknown. In this work, we identified 14 pyrabactin resistance-likes (PYLs), 84 type 2C protein phosphatase (PP2Cs), and 8 SNF1-related protein kinase 2s (SnRK2s) from C. sinensis. The transcriptomic analysis indicated that PYL-PP2C-SnRK2s were associated with changes of leaf color and the response of C. sinensis to drought and salt stressors. Changes of the expression of Snrk2s were not significant in the process of leaf color change or drought and salt stress response, suggesting that PYLs and PP2Cs may not interact with SnRK2s in C. sinensis during these processes. Finally, Gene Regulatory Network (GRN) construction and interaction networks analysis demonstrated that PYLs and PP2Cs were associated with multiple metabolic pathways during the changes of leaf color.

Counteraction of ABA-Mediated Inhibition of Seed Germination and Seedling Establishment by ABA Signaling Terminator in Arabidopsis

Seed germination and seedling establishment are important for the reproductive success of plants, but seeds and seedlings typically encounter constantly changing environmental conditions. By inhibiting seed germination and post-germinative growth through the PYR1/PYL/RCAR ABA receptors and PP2C co-receptors, the phytohormone abscisic acid (ABA) prevents premature germination and seedling growth under unfavorable conditions. However, little is known about how the ABA-mediated inhibition of seed germination and seedling establishment is thwarted. Here, we report that ABA Signaling Terminator (ABT), a WD40 protein, efficiently switches off ABA signaling and is critical for seed germination and seedling establishment. ABT is induced by ABA in a PYR1/PYL/RCAR-PP2C-dependent manner. Overexpression of ABT promotes seed germination and seedling greening in the presence of ABA, whereas knockout of ABT has the opposite effect. We found that ABT interacts with the PYR1/PYL/RCAR and PP2C proteins, interferes with the interaction between PYR1/PYL4 and ABI1/ABI2, and hampers the inhibition of ABI1/ABI2 by ABA-bound PYR1/PYL4, thereby terminating ABA signaling. Taken together, our results reveal a core mechanism of ABA signaling termination that is critical for seed germination and seedling establishment in Arabidopsis.

The Sucrose Non-Fermenting 1-Related Protein Kinase 2 (SnRK2) Genes Are Multifaceted Players in Plant Growth, Development and Response to Environmental Stimuli

Reversible protein phosphorylation orchestrated by protein kinases and phosphatases is a major regulatory event in plants and animals. The SnRK2 subfamily consists of plant-specific protein kinases in the Ser/Thr protein kinase superfamily. Early observations indicated that SnRK2s are mainly involved in response to abiotic stress. Recent evidence shows that SnRK2s are multifarious players in a variety of biological processes. Here, we summarize the considerable knowledge of SnRK2s, including evolution, classification, biological functions and regulatory mechanisms at the epigenetic, post-transcriptional and post-translation levels.

Genome-Wide Identification, Evolution, and Transcriptional Profiling of PP2C Gene Family in Brassica rapa

The type 2C protein which belongs to the major group of protein phosphatases (PP2C) plays a vital role in abscisic acid (ABA) signaling and signal transductions processes. In the present study, 131 PP2C genes were identified in total in Brassica rapa and categorized into thirteen subgroups based on their phylogenetic relationships. These B. rapa PP2C are structurally conserved based on amino acid sequence alignment, phylogenetic analysis, and conserved domains. Moreover, we utilized previously reported RNA-sequence data on various tissues (root, stem, leaf, flower, and silique), which suggests overlapping expression pattern in 29 paralogous gene pairs. The qRT-PCR validation of 15 paralogous gene pairs depicts distinct expression patterns in response to various abiotic stresses, such as heat, cold, ABA, and drought. Interestingly, stress-responsive BraPP2C candidate genes were also identified, suggesting their significance in stress-tolerance mechanism in B. rapa. The evolutionary analysis for 15 paralogous gene pairs suggested that only three pairs have the positive selection and remaining were purifying in nature. The presented results of this study hasten our understanding of the molecular evolution of the PP2C gene family in B. rapa. Thus, it will be ultimately helping in future research for facilitating the functional characterization of BraPP2C genes in developing the abiotic stress tolerant plants.

Genome-wide identification, evolution, and molecular characterization of the PP2C gene family in woodland strawberry

The protein phosphatase 2C (PP2C) gene family is one of the momentous and conserved plant-specific gene families, known to participate in cellular processes via reversible protein phosphorylation and regulates signal transduction in eukaryotic organisms. Recently, PP2Cs were identified in Arabidopsis and maize, however, the whole-genome analysis of PP2C in strawberry has not yet been reported. In the current research, we found 62 PP2C-encoding genes in total from the strawberry genome. Further, the phylogenetic analysis categorized FvPP2C genes into twelve subgroups with significant structural conservation based on conserved domain and amino acid sequence. Moreover, we observed a strong signature of purifying selection between the comparison of orthologous gene pairs of strawberry and Arabidopsis. The comparison of RNA-sequence (RNA-seq) data published on various vegetative and reproductive tissues of strawberry plant suggested the significant role of FvPP2C genes in organ development. The qRT-PCR validation of thirty FvPP2C genes indicated their critical tolerance-related role under abiotic stress stimuli in strawberry. Finally, the subcellular localization of FvPP2C51 gene proves that it resides and stimulates its function in the nucleus. Our findings provide an overview of the identification of strawberry FvPP2C gene family and demonstrate their critical role in tissue-specific response and abiotic stress-tolerance, thereby, intimating their significance in the strawberry molecular breeding for the resistant cultivars.

Abscisic Acid Signaling Inhibits Brassinosteroid Signaling through Dampening the Dephosphorylation of BIN2 by ABI1 and ABI2

Abscisic acid (ABA) and brassinosteroid (BR) antagonistically regulate many aspects of plant growth and development. Previous physiological studies have revealed that the inhibition of BR signaling by ABA is largely dependent on ABI1 and ABI2. However, the genetic and molecular basis of how ABI1 and ABI2 are involved in inhibiting BR signaling remains unclear. Although it is known that in the BR signaling pathway the ABA-BR crosstalk occurs in the downstream of BR receptor complex but upstream of BIN2 kinase, a negative regulator of BR signaling, the component that acts as the hub to directly mediate their crosstalk remains a big mystery. Here, we found that ABI1 and ABI2 interact with and dephosphorylate BIN2 to regulate its activity toward the phosphorylation of BES1. By in vitro mimicking ABA signal transduction, we found that ABA can promote BIN2 phosphorylation by inhibiting ABI2 through ABA receptors. RNA-sequencing analysis further demonstrated that ABA inhibits BR signaling through the ABA primary signaling components, including its receptors and ABI2, and that ABA and GSK3s co-regulate a common set of stress-responsive genes. Because BIN2 can interact with and phosphorylate SnRK2s to activate its kinase activity, our study also reveals there is a module of PP2Cs-BIN2-SnRK2s in the ABA signaling pathway. Collectively, these findings provide significant insights into how plants balance growth and survival by coordinately regulating the growth-promoting signaling pathway and stress responses under abiotic stresses.

The core regulatory network of the abscisic acid pathway in banana: genome-wide identification and expression analyses during development, ripening, and abiotic stress

BACKGROUND

Abscisic acid (ABA) signaling plays a crucial role in developmental and environmental adaptation processes of plants. However, the PYL-PP2C-SnRK2 families that function as the core components of ABA signaling are not well understood in banana.

RESULTS

In the present study, 24 PYL, 87 PP2C, and 11 SnRK2 genes were identified from banana, which was further supported by evolutionary relationships, conserved motif and gene structure analyses. The comprehensive transcriptomic analyses showed that banana PYL-PP2C-SnRK2 genes are involved in tissue development, fruit development and ripening, and response to abiotic stress in two cultivated varieties. Moreover, comparative expression analyses of PYL-PP2C-SnRK2 genes between BaXi Jiao (BX) and Fen Jiao (FJ) revealed that PYL-PP2C-SnRK2-mediated ABA signaling might positively regulate banana fruit ripening and tolerance to cold, salt, and osmotic stresses. Finally, interaction networks and co-expression assays demonstrated that the core components of ABA signaling were more active in FJ than in BX in response to abiotic stress, further supporting the crucial role of the genes in tolerance to abiotic stress in banana.

CONCLUSIONS

This study provides new insights into the complicated transcriptional control of PYL-PP2C-SnRK2 genes, improves the understanding of PYL-PP2C-SnRK2-mediated ABA signaling in the regulation of fruit development, ripening, and response to abiotic stress, and identifies some candidate genes for genetic improvement of banana.

SMAX1-LIKE/D53 Family Members Enable Distinct MAX2-Dependent Responses to Strigolactones and Karrikins in Arabidopsis

The plant hormones strigolactones and smoke-derived karrikins are butenolide signals that control distinct aspects of plant development. Perception of both molecules in Arabidopsis thaliana requires the F-box protein MORE AXILLARY GROWTH2 (MAX2). Recent studies suggest that the homologous SUPPRESSOR OF MAX2 1 (SMAX1) in Arabidopsis and DWARF53 (D53) in rice (Oryza sativa) are downstream targets of MAX2. Through an extensive analysis of loss-of-function mutants, we demonstrate that the Arabidopsis SMAX1-LIKE genes SMXL6, SMXL7, and SMXL8 are co-orthologs of rice D53 that promote shoot branching. SMXL7 is degraded rapidly after treatment with the synthetic strigolactone mixture rac-GR24. Like D53, SMXL7 degradation is MAX2- and D14-dependent and can be prevented by deletion of a putative P-loop. Loss of SMXL6,7,8 suppresses several other strigolactone-related phenotypes in max2, including increased auxin transport and PIN1 accumulation, and increased lateral root density. Although only SMAX1 regulates germination and hypocotyl elongation, SMAX1 and SMXL6,7,8 have complementary roles in the control of leaf morphology. Our data indicate that SMAX1 and SMXL6,7,8 repress karrikin and strigolactone signaling, respectively, and suggest that all MAX2-dependent growth effects are mediated by degradation of SMAX1/SMXL proteins. We propose that functional diversification within the SMXL family enabled responses to different butenolide signals through a shared regulatory mechanism.

Crucial roles of the pentatricopeptide repeat protein SOAR1 in Arabidopsis response to drought, salt and cold stresses

Whereas several mitochondrial/chloroplast pentatricopeptide repeat (PPR) proteins have been reported to regulate plant responses to abiotic stresses, no nucleus-localized PPR protein has been found to play role in these processes. In the present experiment, we provide evidence that a cytosol-nucleus dual-localized PPR protein SOAR1, functioning to negatively regulate abscisic acid (ABA) signaling in seed germination and postgermination growth, is a crucial, positive regulator of plant response to abiotic stresses. Downregulation of SOAR1 expression reduces, but upregulation of SOAR1 expression enhances, ABA sensitivity in ABA-induced promotion of stomatal closure and inhibition of stomatal opening, and plant tolerance to multiple, major abiotic stresses including drought, high salinity and low temperature. Interestingly and importantly, the SOAR1-overexpression lines display strong abilities to tolerate drought, salt and cold stresses, with surprisingly high resistance to salt stress in germination and postgermination growth of seeds that are able to potentially germinate in seawater, while no negative effect on plant growth and development was observed. So, the SOAR1 gene is likely useful for improvement of crops by transgenic manipulation to enhance crop productivity in stressful conditions. Further experimental data suggest that SOAR1 likely regulates plant stress responses at least partly by integrating ABA-dependent and independent signaling pathways, which is different from the ABI2/ABI1 type 2C protein phosphatase-mediated ABA signaling. These findings help to understand highly complicated stress and ABA signalling network.

TaPP2C1, a Group F2 Protein Phosphatase 2C Gene, Confers Resistance to Salt Stress in Transgenic Tobacco

Group A protein phosphatases 2Cs (PP2Cs) are essential components of abscisic acid (ABA) signaling in Arabidopsis; however, the function of group F2 subfamily PP2Cs is currently less known. In this study, TaPP2C1 which belongs to group F2 was isolated and characterized from wheat. Expression of the TaPP2C1-GFP fusion protein suggested its ubiquitous localization within a cell. TaPP2C1 expression was downregulated by abscisic acid (ABA) and NaCl treatments, but upregulated by H2O2 treatment. Overexpression of TaPP2C1 in tobacco resulted in reduced ABA sensitivity and increased salt resistance of transgenic seedlings. Additionally, physiological analyses showed that improved resistance to salt stress conferred by TaPP2C1 is due to the reduced reactive oxygen species (ROS) accumulation, the improved antioxidant system, and the increased transcription of genes in the ABA-independent pathway. Finally, transgenic tobacco showed increased resistance to oxidative stress by maintaining a more effective antioxidant system. Taken together, these results demonstrated that TaPP2C1 negatively regulates ABA signaling, but positively regulates salt resistance. TaPP2C1 confers salt resistance through activating the antioxidant system and ABA-independent gene transcription process.

The dynamics of DNA methylation in maize roots under Pb stress

Plants adapt to adverse conditions through a series of physiological, cellular, and molecular processes, culminating in stress tolerance. However, little is known about the associated regulatory mechanisms at the epigenetic level in maize under lead (Pb) stress. Therefore, in this study, we aimed to compare DNA methylation profiles during the dynamic development of maize roots following Pb treatment to identify candidate genes involved in the response to Pb stress. Methylated DNA immunoprecipitation-sequencing (MeDIP-seq) was used to investigate the genome-wide DNA methylation patterns in maize roots under normal condition (A1) and 3 mM Pb(NO₃)₂ stress for 12 h (K2), 24 h (K3) and 48 h (K4). The results showed that the average methylation density was the highest in CpG islands (CGIs), followed by the intergenic regions. Within the gene body, the methylation density of the introns was higher than those of the UTRs and exons. In total, 3857 methylated genes were found in 4 tested samples, including 1805 differentially methylated genes for K2 versus A1, 1508 for K3 versus A1, and 1660 for K4 versus A1. Further analysis showed that 140 genes exhibited altered DNA methylation in all three comparisons, including some well-known stress-responsive transcription factors and proteins, such as MYB, AP2/ERF, bZIP, serine-threonine/tyrosine-proteins, pentatricopeptide repeat proteins, RING zinc finger proteins, F-box proteins, leucine-rich repeat proteins and tetratricopeptide repeat proteins. This study revealed the genome-scale DNA methylation patterns of maize roots in response to Pb exposure and identified candidate genes that potentially regulate root dynamic development under Pb stress at the methylation level.

Type 2C phosphatase 1 of Artemisia annua L. is a negative regulator of ABA signaling

The phytohormone abscisic acid (ABA) plays an important role in plant development and environmental stress response. Additionally, ABA also regulates secondary metabolism such as artemisinin in the medicinal plant Artemisia annua L. Although an earlier study showed that ABA receptor, AaPYL9, plays a positive role in ABA-induced artemisinin content improvement, many components in the ABA signaling pathway remain to be elucidated in Artemisia annua L. To get insight of the function of AaPYL9, we isolated and characterized an AaPYL9-interacting partner, AaPP2C1. The coding sequence of AaPP2C1 encodes a deduced protein of 464 amino acids, with all the features of plant type clade A PP2C. Transcriptional analysis showed that the expression level of AaPP2C1 is increased after ABA, salt, and drought treatments. Yeast two-hybrid and bimolecular fluorescence complementation assays (BiFC) showed that AaPYL9 interacted with AaPP2C1. The P89S, H116A substitution in AaPYL9 as well as G199D substitution or deletion of the third phosphorylation site-like motif in AaPP2C1 abolished this interaction. Furthermore, constitutive expression of AaPP2C1 conferred ABA insensitivity compared with the wild type. In summary, our data reveals that AaPP2C1 is an AaPYL9-interacting partner and involved in the negative modulation of the ABA signaling pathway in A. annua L.

Arabidopsis pentatricopeptide repeat protein SOAR1 plays a critical role in abscisic acid signalling

A dominant suppressor of the ABAR overexpressor, soar1-1D, from CHLH/ABAR [coding for Mg-chelatase H subunit/putative abscisic acid (ABA) receptor (ABAR)] overexpression lines was screened to explore the mechanism of the ABAR-mediated ABA signalling. The SOAR1 gene encodes a pentatricopeptide repeat (PPR) protein which localizes to both the cytosol and nucleus. Down-regulation of SOAR1 strongly enhances, but up-regulation of SOAR1 almost completely impairs, ABA responses, revealing that SOAR1 is a critical, negative, regulator of ABA signalling. Further genetic evidence supports that SOAR1 functions downstream of ABAR and probably upstream of an ABA-responsive transcription factor ABI5. Changes in the SOAR1 expression alter expression of a subset of ABA-responsive genes including ABI5. These findings provide important information to elucidate further the functional mechanism of PPR proteins and the complicated ABA signalling network.

Transcriptome analysis reveals crosstalk of responsive genes to multiple abiotic stresses in cotton (Gossypium hirsutum L.)

Abiotic stress is a major environmental factor that limits cotton growth and yield, moreover, this problem has become more and more serious recently, as multiple stresses often occur simultaneously due to the global climate change and environmental pollution. In this study, we sought to identify genes involved in diverse stresses including abscisic acid (ABA), cold, drought, salinity and alkalinity by comparative microarray analysis. Our result showed that 5790, 3067, 5608, 778 and 6148 transcripts, were differentially expressed in cotton seedlings under treatment of ABA (1 μM ABA), cold (4°C), drought (200 mM mannitol), salinity (200 mM NaCl) and alkalinity (pH=11) respectively. Among the induced or suppressed genes, 126 transcripts were shared by all of the five kinds of abiotic stresses, with 64 up-regulated and 62 down-regulated. These common members are grouped as stress signal transduction, transcription factors (TFs), stress response/defense proteins, metabolism, transport facilitation, as well as cell wall/structure, according to the function annotation. We also noticed that large proportion of significant differentially expressed genes specifically regulated in response to different stress. Nine of the common transcripts of multiple stresses were selected for further validation with quantitative real time RT-PCR (qRT-PCR). Furthermore, several well characterized TF families, for example, WRKY, MYB, NAC, AP2/ERF and zinc finger were shown to be involved in different stresses. As an original report using comparative microarray to analyze transcriptome of cotton under five abiotic stresses, valuable information about functional genes and related pathways of anti-stress, and/or stress tolerance in cotton seedlings was unveiled in our result. Besides this, some important common factors were focused for detailed identification and characterization. According to our analysis, it suggested that there was crosstalk of responsive genes or pathways to multiple abiotic or even biotic stresses, in cotton. These candidate genes will be worthy of functional study under diverse stresses.