Abscisic Acid Hypersensitivity Research Articles

DEAD-box RNA helicase 6 regulates drought and abscisic acid stress responses in rapeseed (Brassica napus)

DEAD-box RNA helicase is a major subfamily of RNA helicases with vital roles played in plant growth, development, and plant-environment interactions. RNA helicase 6 in rapeseed (Brassica napus) (BnRH6) is a member of DEAD-box RNA helicase. While previous research has demonstrated the role of BnRH6 in salt stress regulation, the involvement of BnRH6 in drought stress adaptation remains unknown. This report described a function of BnRH6 in drought stress response. BnRH6 was sufficiently induced by osmotic stress. Transgenic Brassica napus and Arabidopsis thaliana (Arabidopsis) overexpressing BnRH6 (OE) showed a drought tolerance phenotype, characterized by improved plant growth, increased survival rates, reduced water loss, leaf chlorosis and oxidative stress. Furthermore, BnRH6 was also induced by exogenous abscisic acid (ABA). BnRH6 overexpression plants exhibited ABA hypersensitivity with lagging seed germination, growth stunt and diminished stomatal opening in the presence of ABA, suggesting the involvement of ABA signal. Assessment of several well-identified drought stress responsive genes such as Calcium-dependent Protein Kinase 14 (BnCDPK14), Enhanced Response to ABA1 (BnERA1) and ABA Insensitive 1 (BnABI1) revealed that their expressions were accordingly changed in BnOE plants, possibly with interplays between BnRH6 and those genes. Our data highlighted the functional role of BnRH6, which plays a positive role in active regulation of drought stress response likely through an ABA-dependent manner in rapeseed plants.

An Amur grape VaHsfC1 is involved in multiple abiotic stresses

Plant heat stress transcription factors (Hsfs) belong to a very large gene family and play dominant roles in response to heat stress. Here, we report the functional analysis of VaHsfC1, a class C Hsf gene from Vitis amurensis, and involved in multiple abiotic stresses. The structure of VaHsfC1 contains a typical HSF domain for DNA-binding at N terminus. Phylogenetic analysis revealed that VaHsfC1 belongs to the C1 family of Hsfs. VaHsfC1 was highly induced by heat, cold, exogenous abscisic acid (ABA) and salinity, respectively. Unusually, VaHsfC1was preferentially localized in nucleus, but less in the cytosol. Also, no transcriptional activation was detected for the protein in yeast cells. Ectopic VaHsfC1 expression in Arabidopsis enhanced heat tolerance characterized by the increased survival rate, higher chlorophyll content, reduced electrolyte leakage, and activated expressions of ascorbate peroxidase (Apx2) and heat shock protein (HSP) expression compared to the WT. Interestingly, overexpression of VaHsfC1 in Arabidopsis could also increase the cold tolerance, as reveled from a series changes at the physiological and biochemical steps, as well as at the transcript levels of CORs in the CBF-dependent responsive pathway. Additionally, the growth of VaHsfC1-overexpressing Arabidopsis showed enhanced seed ABA hypersensitivity during germination and cotyledon development, and a significant reduction in stomatal aperture was also observed in overexpression lines. Furthermore, VaHsfC1-overexpressing lines displayed salt-hypersensitive phenotype with a lower rates both in germination and cotyledon greening, and the inhibition of root growth. Our findings demonstrated that the complex nature of VaHsfC1 in mediating multiple abiotic stress responses, as a key component to further understanding of the ‘crosstalk’ mechanism of multiple abiotic stress response in plants.

Involvement of rice transcription factor OsERF19 in response to ABA and salt stress responses

Soil salinity is a major environmental stressor that restricts the growth and yield of crops. Plants have evolved more complicated and precise mechanisms to cope with salt stress, as they cannot escape from harmful environments. In the current study we identified and characterized an AP2/ERF transcription factor in rice, OsERF19. The expression of OsERF19 was slightly repressed by salt stress or abscisic acid (ABA) treatment. OsERF19-overexpression (OsERF19-OX) plants displayed enhanced tolerance to salt stress and ABA hypersensitivity compared to wild type and control plants. Furthermore, OsLEA3, OsNHX1, OsHKT6, and OsOTS1 were upregulated in OsERF19-OX plants when the plants were subjected to salt stress. OsRAB21, OsNCED5, and OsP5CS1 were also upregulated in OsERF19-OX plants treated with ABA. Yeast one-hybrid and dual luciferase reporter assays demonstrated that OsERF19 directly targets the promoters of OsOTS1 and OsNCED5 and further increases their transcription. These results suggest that the transcription factor OsERF19 plays a positive role in salt stress and ABA responses in rice.

Arabidopsis N6-methyladenosine reader CPSF30-L recognizes FUE signals to control polyadenylation site choice in liquid-like nuclear bodies

The biological functions of the epitranscriptomic modification N6-methyladenosine (m6A) in plants are not fully understood. CPSF30-L is a predominant isoform of the polyadenylation factor CPSF30 and consists of CPSF30-S and an m6A-binding YTH domain. Little is known about the biological roles of CPSF30-L and the molecular mechanism underlying its m6A-binding function in alternative polyadenylation. Here, we characterized CPSF30-L as an Arabidopsis m6A reader whose m6A-binding function is required for the floral transition and abscisic acid (ABA) response. We found that the m6A-binding activity of CPSF30-L enhances the formation of liquid-like nuclear bodies, where CPSF30-L mainly recognizes m6A-modified far-upstream elements to control polyadenylation site choice. Deficiency of CPSF30-L lengthens the 3′ untranslated region of three phenotypes-related transcripts, thereby accelerating their mRNA degradation and leading to late flowering and ABA hypersensitivity. Collectively, this study uncovers a new molecular mechanism for m6A-driven phase separation and polyadenylation in plants.

Overexpression of a Poplar RING-H2 Zinc Finger, Ptxerico, Confers Enhanced Drought Tolerance via Reduced Water Loss and Ion Leakage in Populus.

Drought stress is one of the major environmental problems in the growth of crops and woody perennials, but it is getting worse due to the global climate crisis. XERICO, a RING (Really Interesting New Gene) zinc-finger E3 ubiquitin ligase, has been shown to be a positive regulator of drought tolerance in plants through the control of abscisic acid (ABA) homeostasis. We characterized a poplar (Populus trichocarpa) RING protein family and identified the closest homolog of XERICO called PtXERICO. Expression of PtXERICO is induced by both salt and drought stress, and by ABA treatment in poplars. Overexpression of PtXERICO in Arabidopsis confers salt and ABA hypersensitivity in young seedlings, and enhances drought tolerance by decreasing transpirational water loss. Consistently, transgenic hybrid poplars overexpressing PtXERICO demonstrate enhanced drought tolerance with reduced transpirational water loss and ion leakage. Subsequent upregulation of genes involved in the ABA homeostasis and drought response was confirmed in both transgenic Arabidopsis and poplars. Taken together, our results suggest that PtXERICO will serve as a focal point to improve drought tolerance of woody perennials.

ABI5 modulates seed germination via feedback regulation of the expression of the PYR/PYL/RCAR ABA receptor genes.

As abscisic acid (ABA) receptors, PYR1/PYL/RCAR (PYLs) play important roles in ABA-mediated seed germination, but the regulation of PYLs in this process, especially at the transcriptional level, remains unclear. In this study, we found that expression of 11 of 14 PYLs changes significantly during seed germination and is affected by exogenous ABA. Two PYLs, PYL11 and PYL12, both of which are expressed specifically in mature seeds, positively modulate ABA-mediated seed germination. However, ABI5 was found to modulate the PYL11- and PYL12-mediated ABA response. In the abi5-7 mutant, ABA hypersensitivity caused by PYL11 and PYL12 overexpression was totally or partially blocked. By contrast, ABI5 regulates the expression of PYL11 and PYL12 by directly binding to their promoters. Moreover, the expression of eight other PYLs is also affected during the germination of abi5 mutants. Promoter analysis revealed that an ABI5-binding region is present next to the TATA box or initiator box. Together, our data demonstrate the role of PYL11 and PYL12 in seed germination. In addition, the identification of PYLs as targets of ABI5 reveals a role of ABI5 in the feedback regulation of ABA-mediated seed germination.

E3 ubiquitin ligase ATL61 acts as a positive regulator in abscisic acid mediated drought response in Arabidopsis

Abscisic acid (ABA) is an important plant hormone that mediates abiotic stresses in plant growth and development. A number of E3 ligases have been reported to be involved in ABA signaling pathway. In this study, we identified a C3H2C3 RING-type E3 ligase, Arabidopsis thaliana Tόxicos en Levadura 61 (ATL61), which regulated drought stress in planta. Enzyme assay in vitro demonstrated that ATL61 had E3 ubiquitin ligase activity, while point mutation of ATL61H109A, H122A (mATL61) abolished its E3 ubiquitin ligase activity. ATL61 overexpression plants exhibited ABA hypersensitivity and were more tolerant to drought, while the atl61 mutant plants were insensitive to ABA. Moreover, mATL61 overexpression lines exhibited similar ABA-related phenotypes with wild type (WT) plants. The transcript abundances of ABA-mediated drought stress-related genes RD20 and RD22 were higher in ATL61 overexpression plants than those in WT, atl61, and mATL61 plants. Our results indicated that ATL61 acted as a positive regulator in the ABA-mediated drought stress response.

Overexpression of the persimmon abscisic acid β-glucosidase gene (DkBG1) alters fruit ripening in transgenic tomato.

β-Glucosidases (BG) are present in many plant tissues. Among these, abscisic acid (ABA) β-glucosidases are thought to take part in the adjustment of cellular ABA levels, however the role of ABA-BG in fruits is still unclear. In this study, through RNA-seq analysis of persimmon fruit, 10 full-length DkBG genes were isolated and were all found to be expressed. In particular, DkBG1 was highly expressed in persimmon fruits with a maximum expression 95days after full bloom (DAFD). We verified that, in vitro, DkBG1 protein can hydrolyze ABA-glucose ester (ABA-GE) to release free ABA. Compared with wild-type, tomato plants that overexpressed DkBG1 significantly upregulated the expression of ABA receptor PYL3/7 genes and showed typical symptoms of ABA hypersensitivity in fruits. DkBG1 overexpression (DkBG1-OE) accelerated fruit ripening onset by 3-4days by increasing ABA levels at the pre-breaker stage and induced early ethylene release compared with wild-type fruits. DkBG1-OE altered the expression of ripening regulator NON-RIPENING (NOR) and its target genes; this in turn altered fruit quality traits such as coloration. Our results demonstrated that DkBG1 plays an important role in fruit ripening and quality by adjusting ABA levels via hydrolysis of ABA-GE.

The ABA receptor-like gene VyPYL9 from drought-resistance wild grapevine confers drought tolerance and ABA hypersensitivity in Arabidopsis

The PYR/PYL/RCAR (hereafter referred to PYLs) proteins, which act as abscisic acid (ABA) receptors, have been reported to play a crucial role in response to drought stress. In this study, we used a drought-resistant accession of the wild Chinese grapevine, Vitis yeshanensis-’Yanshan-1’, as a model to understand the function of PYLs in grape and other fruit crops. We cloned six PYL genes from V. yeshanensis. Phylogenetic analysis showed that the encoded proteins could be classified into three subfamilies. All six grapevine PYL proteins contained conserved amino acids at positions implicated in ‘gate-and-latch’ mechanism of ABA binding and in the interaction with PP2C proteins. Gene expression profiles of VyPYLs in various tissues of ‘Yanshan-1’ plants revealed they were relatively strongly expressed in old leaves compared to young leaves. Analysis of the subcellular localization of the VyPYL proteins showed that they were localized in the cytoplasm and the nucleus. Yeast two-hybrid assays revealed that six VyPYL proteins selectively interacted with three VyPP2C proteins in an ABA-dependent or ABA-independent manner. Expression of one of the genes, VyPYL9, was induced by exogenous ABA and drought conditions. Heterologous expression of VyPYL9 in Arabidopsis enhanced ABA sensitivity during seed germination and primary root growth. Moreover, VyPYL9-expressing Arabidopsis plants showed enhanced drought tolerance, and this was associated with decreased water loss and increased activity of antioxidant defense systems. In addition, we found that ABA promoted leaf senescence in Arabidopsis plants expressing VyPYL9. Taken together, our results suggest that VyPYL9 may be involved in response of grapevine to drought stress via the ABA signaling pathway. VyPYL9-expressing Arabidopsis plants showed enhanced drought tolerance, and this was associated with decreased water loss and increased activity of antioxidant defense systems. In addition, we found that ABA promoted leaf senescence in Arabidopsis plants expressing VyPYL9.

Arabidopsis ALIX Regulates Stomatal Aperture and Turnover of Abscisic Acid Receptors.

The plant endosomal trafficking pathway controls the abundance of membrane-associated soluble proteins, as shown for abscisic acid (ABA) receptors of the PYRABACTIN RESISTANCE1/PYR1-LIKE/REGULATORY COMPONENTS OF ABA RECEPTORS (PYR/PYL/RCAR) family. ABA receptor targeting for vacuolar degradation occurs through the late endosome route and depends on FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING1 (FYVE1) and VACUOLAR PROTEIN SORTING23A (VPS23A), components of the ENDOSOMAL SORTING COMPLEX REQUIRED FOR TRANSPORT-I (ESCRT-I) complexes. FYVE1 and VPS23A interact with ALG-2 INTERACTING PROTEIN-X (ALIX), an ESCRT-III-associated protein, although the functional relevance of such interactions and their consequences in cargo sorting are unknown. In this study we show that Arabidopsis (Arabidopsis thaliana) ALIX directly binds to ABA receptors in late endosomes, promoting their degradation. Impaired ALIX function leads to altered endosomal localization and increased accumulation of ABA receptors. In line with this activity, partial loss-of-function alix-1 mutants display ABA hypersensitivity during growth and stomatal closure, unveiling a role for the ESCRT machinery in the control of water loss through stomata. ABA-hypersensitive responses are suppressed in alix-1 plants impaired in PYR/PYL/RCAR activity, in accordance with ALIX affecting ABA responses primarily by controlling ABA receptor stability. ALIX-1 mutant protein displays reduced interaction with VPS23A and ABA receptors, providing a molecular basis for ABA hypersensitivity in alix-1 mutants. Our findings unveil a negative feedback mechanism triggered by ABA that acts via ALIX to control the accumulation of specific PYR/PYL/RCAR receptors.

OoNAC72, a NAC-Type Oxytropis ochrocephala Transcription Factor, Conferring Enhanced Drought and Salt Stress Tolerance in Arabidopsis.

The NAC proteins form one of the largest families of plant-specific transcription factors (TFs) and play essential roles in developmental processes and stress responses. In this study, we characterized a NAC domain transcription factor, OoNAC72, from a legume Oxytropis ochrocephala. OoNAC72 was proved to be localized in the nuclei in tobacco lower epidermal cells and had transcriptional activation activity in yeast, confirming its transcription activity. OoNAC72 expression could be induced by drought, salinity and exogenous abscisic acid (ABA) in O. ochrocephala seedlings. Furthermore, over-expression of OoNAC72 driven by CaMV35S promoter in Arabidopsis resulted in ABA hypersensitivity and enhanced tolerance to drought and salt stresses during seed germination and post-germinative growth periods. In addition, over-expression of OoNAC72 enhanced the expression of stress-responsive genes such as RD29A, RD29B, RD26, LEA14, ANACOR19, ZAT10, PP2CA, and NCED3. These results highlight the important regulatory role of OoNAC72 in multiple abiotic stress tolerance, and may provide an underlying reason for the spread of O. ochrocephala.

A Stress-Responsive NAC Transcription Factor from Tiger Lily (LlNAC2) Interacts with LlDREB1 and LlZHFD4 and Enhances Various Abiotic Stress Tolerance in Arabidopsis.

Our previous studies have indicated that a partial NAC domain protein gene is strongly up-regulated by cold stress (4 °C) in tiger lily (Lilium lancifolium). In this study, we cloned the full-length of this NAC gene, LlNAC2, to further investigate the function of LlNAC2 in response to various abiotic stresses and the possible involvement in stress tolerance of the tiger lily plant. LlNAC2 was noticeably induced by cold, drought, salt stresses, and abscisic acid (ABA) treatment. Promoter analysis showed that various stress-related cis-acting regulatory elements were located in the promoter of LlNAC2; and the promoter was sufficient to enhance activity of GUS protein under cold, salt stresses and ABA treatment. DREB1 (dehydration-responsive binding protein1) from tiger lily (LlDREB1) was proved to be able to bind to the promoter of LlNAC2 by yeast one-hybrid (Y1H) assay. LlNAC2 was shown to physically interact with LlDREB1 and zinc finger-homeodomain ZFHD4 from the tiger lily (LlZFHD4) by bimolecular fluorescence complementation (BiFC) assay. Overexpressing LlNAC2 in Arabidopsis thaliana showed ABA hypersensitivity and enhanced tolerance to cold, drought, and salt stresses. These findings indicated LlNAC2 is involved in both DREB/CBF-COR and ABA signaling pathways to regulate stress tolerance of the tiger lily.

The B-box protein BBX19 suppresses seed germination via induction of ABI5.

Seed germination is a fundamental process in the plant life cycle and is regulated by functionally opposing internal and external inputs. Here we explored the role of a negative regulator of photomorphogenesis, a B-box-containing protein (BBX19), as a molecular link between the inhibitory action of the phytohormone abscisic acid (ABA) and the promoting role of light in germination. We show that seeds of BBX19-overexpressing lines, in contrast to those of BBX19 RNA interference lines, display ABA hypersensitivity, albeit independently of elongated hypocotyl 5 (HY5). Moreover, we establish that BBX19 functions neither via perturbation of GA signaling, the ABA antagonistic phytohormone, nor through interference with the DELLA protein germination repressors. Rather, BBX19 functions as an inducer of ABA INSENSITIVE5 (ABI5) by binding to the light-responsive GT1 motifs in the gene promoter. In summary, we identify BBX19 as a regulatory checkpoint, directing diverse developmental processes and tailoring adaptive responses to distinct endogenous and exogenous signals.

Arabidopsis histone H3K4 demethylase JMJ17 functions in dehydration stress response.

Under dehydration in plants, antagonistic activities of histone 3 lysine 4 (H3K4) methyltransferase and histone demethylase maintain a dynamic and homeostatic state of gene expression by orientating transcriptional reprogramming toward growth or stress tolerance. However, the histone demethylase that specifically controls histone methylation homeostasis under dehydration stress remains unknown. Here, we document that a histone demethylase, JMJ17, belonging to the KDM5/JARID1 family, plays crucial roles in response to dehydration stress and abscisic acid (ABA) in Arabidopsis thaliana. jmj17 loss-of-function mutants displayed dehydration stress tolerance and ABA hypersensitivity in terms of stomatal closure. JMJ17 specifically demethylated H3K4me1/2/3 via conserved iron-binding amino acids invitro and invivo. Moreover, H3K4 demethylase activity of JMJ17 was required for dehydration stress response. Systematic combination of genome-wide chromatin immunoprecipitation coupled with massively parallel DNA sequencing (ChIP-seq) and RNA-sequencing (RNA-seq) analyses revealed that a loss-of-function mutation in JMJ17 caused an ectopic increase in genome-wide H3K4me3 levels and activated a plethora of dehydration stress-responsive genes. Importantly, JMJ17 bound directly to the chromatin of OPEN STOMATA 1 (OST1) and demethylated H3K4me3 for the regulation of OST1 mRNA abundance, thereby modulating the dehydration stress response. Our results demonstrate a new function of a histone demethylase under dehydration stress in plants.

GOLDEN2-LIKE Transcription Factors Regulate WRKY40 Expression in Response to Abscisic Acid

Arabidopsis (Arabidopsis thaliana) GARP (Golden2, ARR-B, Psr1) family transcription factors, GOLDEN2-LIKE1 and -2 (GLK1/2), function in different biological processes; however, whether and how these transcription factors modulate the response to abscisic acid (ABA) remain unknown. In this study, we used a glk1 glk2 double mutant to examine the role of GLK1/2 in the ABA response. The glk1 glk2 double mutant displayed ABA-hypersensitive phenotypes during seed germination and seedling development and an osmotic stress-resistant phenotype during seedling development. Genome-wide RNA sequencing analysis of the glk1 glk2 double mutant revealed that GLK1/2 regulate several ABA-responsive genes, including WRKY40, in the presence of ABA. Chromatin immunoprecipitation and gel retardation assays showed that GLK1/2 directly associate with the WRKY40 promoter via the recognition of a consensus sequence. Additionally, RNA sequencing analysis of the glk1 glk2 double mutant and wrky40 single mutant revealed that GLK1/2 and WRKY40 control a common set of downstream target genes in response to ABA. Furthermore, results of a genetic interaction test showed that the glk1 glk2 wrky40 triple mutant displayed similar ABA hypersensitivity to the wrky40 single mutant and the glk1 glk2 double mutant, while the glk1 glk2 wrky40 abi5-c (ABI5 CRISPR/Cas9 mutant) quadruple mutant displayed similar ABA hyposensitivity to the abi5-7 single mutant. Based on these results, we propose that the GLK1/2-WRKY40 transcription module plays a negative regulatory role in the ABA response.

Arabidopsis RIBOSOMAL RNA PROCESSING7 Is Required for 18S rRNA Maturation.

Ribosome biogenesis is fundamental to growth and development in eukaryotes and is linked to human diseases and cancer. Arabidopsis thaliana MORPHOLOGY OF ARGONAUTE1-52 SUPPRESSED 2 (MAS2) participates in splicing and 45S ribosomal DNA (rDNA) expression. In a screen for MAS2 interactors, we identified RIBOSOMAL RNA PROCESSING 7 (RRP7), an ortholog of yeast rRNA processing protein 7 (Rrp7), which is required for 18S ribosomal RNA (rRNA) maturation. Arabidopsis rrp7 mutants exhibit a pleiotropic phenotype including slow growth, altered shoot phyllotaxy, aberrant venation in lateral organs, partial infertility, and abscisic acid hypersensitivity in seedlings. In Arabidopsis, RRP7 localizes mainly to the nucleolus, the site of the 45S rDNA transcription that produces a 45S pre-rRNA primary transcript, precursor of the 25S, 18S and 5.8S rRNAs. Lack of RRP7 function perturbs 18S rRNA maturation, causes nucleolar hypertrophy, and results in an increased 25S/18S rRNA ratio. Arabidopsis contains hundreds of 45S rDNA genes whose expression is epigenetically regulated, and deregulated, in rrp7 mutants. Double mutant analysis revealed synergistic interactions between RRP7 alleles and alleles of MAS2, NUCLEOLIN1 (NUC1), and HISTONE DEACETYLASE 6 (HDA6), which encode epigenetic regulators of 45S rDNA transcription. Our results reveal the evolutionarily conserved but divergent roles of RRP7 as a ribosome biogenesis factor.

A DEAD-box RNA helicase, RH8, is critical for regulation of ABA signalling and the drought stress response via inhibition of PP2CA activity.

Abscisic acid (ABA) is major plant hormone involved in regulating abiotic stress responses. Several studies have established that an ABA-signalling transduction pathway-from ABA perception to response-functions in plant cells. The group A PP2Cs constitute core components of ABA signalling, and they negatively regulate ABA signalling and stress responses. Recent studies have identified and functionally analysed regulators of PP2C activity; however, the precise regulatory mechanisms remain unclear. In the present study, we used a yeast 2-hybrid (Y2H) screening analysis to identify the DEAD-box RNA helicase RH8, which interacted with PP2CA in the nucleus. rh8 knockout mutants exhibited ABA hyposensitivity and drought-susceptible phenotypes characterized by high levels of transpirational water loss via reduced stomatal closure and decreased leaf temperatures. However, rh8/pp2ca double mutants showed ABA hypersensitivity and drought-tolerant phenotypes, indicating that RH8 and PP2CA function in the same ABA-signalling pathway in the drought stress response; moreover, RH8 functions upstream of PP2CA. In vitro phosphatase and kinase assays revealed that RH8 inhibits PP2CA phosphatase activity. Our data indicate that RH8 and its interacting partner PP2CA modulate the drought stress response via ABA-dependent signalling.

The Antagonistic Action of Abscisic Acid and Cytokinin Signaling Mediates Drought Stress Response in Arabidopsis

As sessile organisms, plants encounter a variety of environmental stresses and must optimize their growth for survival. Abscisic acid (ABA) and cytokinin antagonistically regulate many developmental processes and environmental stress responses in plants. However, the molecular mechanism underlying this antagonism remains poorly defined. In this study, we demonstrated that Sucrose nonfermenting1-related kinases SnRK2.2, SnRK2.3, and SnRK2.6, the key kinases of the ABA signaling pathway, directly interact with and phosphorylate type-A response regulator 5 (ARR5), a negative regulator of cytokinin signaling. The phosphorylation of ARR5 Ser residues by SnRK2s enhanced ARR5 protein stability. Accordingly, plants overexpressing ARR5 showed ABA hypersensitivity and drought tolerance, and these phenotypes could not be recapitulated by overexpressing a non-phosphorylated ARR5 mimic. Moreover, the type-B ARRs, ARR1, ARR11 and ARR12, physically interacted with SnRK2s and repressed the kinase activity of SnRK2.6. The arr1,11,12 triple mutant exhibited hypersensitivity to ABA. Genetic analysis demonstrated that SnRK2s act upstream of ARR5 but downstream of ARR1, ARR11 and ARR12 in mediating ABA response and drought tolerance. Taken together, this study unravels the antagonistic actions of several molecular components of the ABA and cytokinin signaling pathways in mediates drought stress response, providing significant insights into how plants coordinate growth and drought stress response by integrating multiple hormone pathways.

The sHSP22 Heat Shock Protein Requires the ABI1 Protein Phosphatase to Modulate Polar Auxin Transport and Downstream Responses.

The phytohormones abscisic acid (ABA) and indole-3-acetic acid (IAA) response pathways interact synergistically or antagonistically to regulate plant development and environmental adaptation. Here, we show that ABI1, a key negative regulator of ABA signaling, is essential for auxin-modulated root development. We performed a microarray analysis using the loss-of-function mutant abi1-3 and Col-0 seedlings treated with IAA. For sHSP22, an endoplasmic reticulum (ER) small heat shock protein-encoding gene, the induction by IAA was dependent on ABI1shsp22 displayed enhanced sensitivity to ABA in primary root growth. In contrast, overexpression of full-length, but not truncated sHSP22 lacking signal peptide and ER-retention sequences, resulted in decreased ABA sensitivity. Overexpressed (OX) sHSP22 partially rescued the ABA hypersensitivity of abi1-3 In addition, sHSP22 is involved in auxin-regulated hypocotyl elongation at high temperature treatment. sHSP22 also affected accumulation of auxin efflux carrier PIN proteins due to potentiated intracellular trafficking. And sHSP22 OX lines initiated more lateral roots after auxin application. Our results suggest that sHSP22 regulates auxin response through modulating auxin polar transport, and ABI1-sHSP22 provides a novel module orchestrating ABA and auxin signaling crosstalk in Arabidopsis (Arabidopsis thaliana).

Ectopic Expression of Pumpkin NAC Transcription Factor CmNAC1 Improves Multiple Abiotic Stress Tolerance in Arabidopsis.

Drought, cold and salinity are the major environmental stresses that limit agricultural productivity. NAC transcription factors regulate the stress response in plants. Pumpkin (Cucurbita moschata) is an important cucurbit vegetable crop and it has strong resistance to abiotic stress; however, the biological functions of stress-related NAC genes in this crop are largely unknown. This study reports the function of CmNAC1, a stress-responsive pumpkin NAC domain protein. The CmNAC1-GFP fusion protein was transiently expressed in tobacco leaves for subcellular localization analysis, and we found that CmNAC1 is localized in the nucleus. Transactivation assay in yeast cells revealed that CmNAC1 functions as a transcription activator, and its transactivation domain is located in the C-terminus. CmNAC1 was ubiquitously expressed in different organs, and its transcript was induced by salinity, cold, dehydration, H2O2, and abscisic acid (ABA) treatment. Furthermore, the ectopic expression (EE) of CmNAC1 in Arabidopsis led to ABA hypersensitivity and enhanced tolerance to salinity, drought and cold stress. In addition, five ABA-responsive elements were enriched in CmNAC1 promoter. The CmNAC1-EE plants exhibited different root architecture, leaf morphology, and significantly high concentration of ABA compared with WT Arabidopsis under normal conditions. Our results indicated that CmNAC1 is a critical factor in ABA signaling pathways and it can be utilized in transgenic breeding to improve the abiotic stress tolerance of crops.