Abscisic Acid Signaling Research Articles

Identification of ABA Signaling Pathway Genes and Their Differential Regulation in Response to Suboptimal Light Stress in Grape (Vitis vinifera L.)

Suboptimal light stress in grapevines is increasing worldwide with the spread of grapevine cultivation, which can affect grapevine physiology and productivity, such as in Southern China. Abscisic acid (ABA) is an important hormone in plant adaptive responses to abiotic stress, including low light stress. However, ABA signaling pathway genes (APGs) are not well characterized in the grapevine, and little is known of their potentially mitigating role in grapevine growth under weak light stress. Our study aimed to explore the potential role of the ABA signaling pathway in the response of grapevines to suboptimal light conditions. In this study, APGs were identified in the grapevine genome, and the distribution of conserved motifs was shown to reflect their phylogenetic relationships. Gene duplication analysis indicated that segmental duplication was an important driver for gene expansion in the grapevine ABA signaling pathway. Suboptimal conditions of light were shown to seriously affect the growth of grapevine leaves and berries, with the differential regulation of APGs in the grapevine. Our study summarizes the basic characteristics of APGs in grapevine, which can now be examined further for their roles in grapevine’s response to suboptimal light conditions.

PYL Family Genes from Liriodendron chinense Positively Respond to Multiple Stresses.

The phytohormone abscisic acid (ABA) plays important roles in response to abiotic and biotic stresses in plants. Pyrabactin resistance 1-like (PYR/PYL) proteins are well-known as ABA receptors, which are responsible for ABA signal transduction. Nevertheless, the characteristics of PYL genes from Liriodendron chinense, an endangered timber tree, remain unclear in coping with various stresses. In this study, five PYLs were identified from the genome of Liriodendron chinense by sequence alignment and conserved motif analysis, which revealed that these LcPYLs contain a conserved gate and latch motif for ABA binding. The LcPYL promoters possess a series of cis-acting elements involved in response to various hormone and abiotic stresses. Moreover, the transcriptome data of Liriodendron hybrid leaves reveal that LcPYL genes specifically transcript under different abiotic stresses; Lchi11622 transcription was induced by drought and cold treatment, and Lchi01385 and Lchi16997 transcription was upregulated under cold and hot stress, respectively. Meanwhile, the LcPYLs with high expression levels shown in the transcriptomes were also found to be upregulated in whole plants treated with the same stresses tested by qPCR. Moreover, under biotic stress caused by scale insect and whitefly, Liriodendron hybrid leaves exhibited a distinct phenotype including disease spots that are dark green in the middle and yellow on the margin; the qPCR results showed that the relative expression levels of Lchi13641 and Lchi11622 in infected leaves were upregulated by 1.76 and 3.75 folds relative to normal leaves, respectively. The subcellular localizations of these stress-responsive LcPYLs were also identified in protoplasts of Liriodendron hybrid. These results provide a foundation to elucidate the function of PYLs from this elite tree species and assist in understanding the molecular mechanism of Liriodendron hybrid in dealing with abiotic and biotic stresses. In future research, the detailed biological function of LcPYLs and the genetic redundancy between LcPYLs can be explored by gene overexpression and knockout based on this study.

Transcript-wide identification and expression pattern analysis to comprehend the roles of AP2/ERF genes under development and abiotic stress in Trichosanthes kirilowii

BackgroundThe APETALA 2/ ethylene-responsive element binding factors (AP2/ERF), are thought to be associated with plant abiotic stress response, and involved in some plant hormone signaling pathways. Trichosanthes kirilowii is an important edible and medicinal crop, so far no research has been conducted on the TkAP2/ERF genes.ResultIn this study, a total of 135 TkERFs were identified, these genes were divided into 4 subfamilies and clustered into 13 groups. Moreover, 37 paralogous pairs were identified, with only two having Ka/Ks values greater than 1, proving that most TkERF genes underwent purifying selection during evolution. Co-expression networks constructed using transcriptome data at various flowering stages revealed that 50, 64, and 67 AP2/ERF genes correlated with members of the ethylene, gibberellin, and abscisic acid signaling pathways, respectively. When tissue cultured seedlings were treated with ETH, GA3 and ABA, 11, 12 and 17 genes were found to be up-regulated, respectively, suggesting that some members of the TkERF gene family may be involved in plant hormone signaling pathways. And under 4 ℃, PEG and NaCl treatment, 15, 20 and 19 genes were up-regulated, respectively, this suggested that these selected genes might be involved in plant abiotic stresses.ConclusionsOverall, we identified 135 AP2/ERF family members, a comprehensive analysis of AP2/ERF gene expression patterns by RNA-seq and qRT-PCR showed that they played important roles in flower development and abiotic stress. This study provided a theoretical basis for the functional study of TkAP2/ERF genes and the genetic improvement of T. kirilowii.

Exogenous spraying of IAA improved the efficiency of microspore embryogenesis in Wucai (Brassica campestris L.) by affecting the balance of endogenous hormones, energy metabolism, and cell wall degradation

BackgroundMicrospore embryogenesis is an extraordinarily complicated process, comprehensively regulated by a composite network of physiological and molecular factors, among which hormone is one of the most crucial factors. Auxin is required for stress-induced microspore reprogramming, however, the mechanism of its regulation of microspore embryogenesis is still unclear.ResultsIn this study, we found exogenously spraying 100 mg·L− 1 IAA on the buds of Wucai significantly increased the rate of microspore embryogenesis, and moreover accelerated the process of embryogenesis. Physiological and biochemical tests showed that the contents of amino acids, soluble total sugar, soluble protein, and starch were significantly increased after IAA treatment. Furthermore, exogenously spraying 100 mg·L− 1 IAA significantly enhanced IAA, GA4, and GA9 content, increased catalase (CAT) and malondialdehyde (MDA) activity, and reduced abscisic acid (ABA), MDA and soluble protopectin content, H2O2 and O2·− production rate in the bud with the largest population of late-uninucleate-stage microspores. Transcriptome sequencing was performed on buds respectively treated with 100 mg·L− 1 IAA and fresh water. A total of 2004 DEGs were identified, of which 79 were involved in micropores development, embryonic development and cell wall formation and modification, most of which were upregulated. KEGG and GO analysis revealed that 9.52% of DEGs were enriched in plant hormone synthesis and signal transduction pathways, pentose and glucuronic acid exchange pathways, and oxidative phosphorylation pathways.ConclusionsThese findings indicated that exogenous IAA altered the contents of endogenous hormone content, total soluble sugar, amino acid, starch, soluble protein, MDA and protopectin, the activities of CAT and peroxidase (POD), and the production rate of H2O2 and O2·−. Combined with transcriptome analysis, it was found that most genes related to gibberellin (GA) and Auxin (IAA) synthesis and signal transduction, pectin methylase (PME) and polygalacturonase (PGs) genes and genes related to ATP synthesis and electron transport chain were upregulated, and genes related to ABA synthesis and signal transduction were downregulated. These results indicated that exogenous IAA treatment could change the balance of endogenous hormones, accelerate cell wall degradation, promote ATP synthesis and nutrient accumulation, inhibit ROS accumulation, which ultimately promote microspore embryogenesis.

The role of walnut bZIP genes in explant browning

BackgroundBasic leucine zipper (bZIP) proteins are important transcription factors in plants. To study the role of bZIP transcription factors in walnut explant browning, this study used bioinformatics software to analyze walnut bZIP gene family members, along with their transcript levels in different walnut tissues, to evaluate the transcriptional expression of this gene family during the primary culture of walnut explants and to reveal the mechanism of action of walnut bZIP genes in walnut explant browning.ResultsThe results identified 65 JrbZIP genes in the walnut genome, which were divided into 8 subfamilies and distributed on 16 chromosomes. The results of transcriptome data analysis showed that there were significant differences in the expression of four genes, namely, JrbZIP55, JrbZIP70, JrbZIP72, and JrbZIP88, under both vermiculite and agar culture conditions. There were multiple hormone (salicylic acid, abscisic acid, auxin, and gibberellin) signaling and regulatory elements that are responsive to stress (low temperature, stress, and defense) located in the promoter regions of JrbZIP55, JrbZIP70, JrbZIP72, and JrbZIP88. The walnut JrbZIP55 protein and Arabidopsis bZIP42 protein are highly homologous, and the proteins interacting with Arabidopsis bZIP42 include the AT2G19940 oxidoreductases, which act on aldehyde or oxygen-containing donors.ConclusionIt is speculated that JrbZIP55 may participate in the regulation of browning in walnut explants.

Heat shock protein TaHSP17.4, a TaHOP interactor in wheat, improves plant stress tolerance

Adaptation to drought and salt stresses is a fundamental part of plant cell physiology and is of great significance for crop production under environmental stress. Heat shock proteins (HSPs) are molecular chaperones that play a crucial role in folding, assembling, translocating, and degrading proteins. However, their underlying mechanisms and functions in stress tolerance remain elusive. Here, we identified the HSP TaHSP17.4 in wheat by analyzing the heat stress-induced transcriptome. Further analysis showed that TaHSP17.4 was significantly induced under drought, salt, and heat stress treatments. Intriguingly, yeast-two-hybrid analysis showed that TaHSP17.4 interacts with the HSP70/HSP90 organizing protein (HOP) TaHOP, which plays a significant role in linking HSP70 and HSP90. We found that TaHSP17.4- and TaHOP-overexpressing plants have a higher proline content and a lower malondialdehyde content than wild-type plants under stress conditions and display strong tolerance to drought, salt, and heat stress. Additionally, qRT-PCR analysis showed that stress-responsive genes relevant to reactive oxygen species scavenging and abscisic acid signaling pathways were significantly induced in TaHSP17.4- and TaHOP-overexpressing plants under stress conditions. Together, our findings provide insight into HSP functions in wheat and two novel candidate genes for improvement of wheat varieties.

Transcriptomic and proteomic analyses of Mangifera indica in response to Xanthomonas critis pv. mangiferaeindicae.

Mango is an important tropical fruit with the reputation of "Tropical Fruit King." It is widely cultivated in tropical and subtropical regions. Mango bacterial leaf spot, which is caused by Xanthomonas critis pv. mangiferaeindicae (Xcm), poses a great threat to the development of mango planting industry. In this study, we used RNA sequencing and data-independent acquisition techniques to compare the transcriptome and proteome of the highly resistant cultivar "Renong No.1" (RN) and the highly susceptible cultivar "Keitt" (KT) in response to Xcm infection at different stages (0, 2, and 6 days). A total of 14,397 differentially expressed genes (DEGs) were identified in the transcriptome of the two varieties, and 4,400 and 8,926 genes were differentially expressed in RN and KT, respectively. Among them, 217 DEGs were related to plant hormone signaling pathway, and 202 were involved in the maintenance of cellular redox homeostasis. A total of 3,438 differentially expressed proteins (DEPs) were identified in the proteome of the two varieties. Exactly 1,542 and 1,700 DEPs were detected in RN and KT, respectively. In addition, 39 DEPs were related to plant hormone signaling pathway, whereas 68 were involved in the maintenance of cellular redox homeostasis. Through cross-validation of the two omics, 1,470 genes were found to be expressed in both groups, and a large number of glutathione metabolism-related genes, such as HSP26-A, G6PD4, and GPX2, were up-regulated in both omics. Peroxisome-related genes, such as LACS6, LACS9, PED1, GLO4, and HACL, were up-regulated or down-regulated in both omics. ABCB11, SAPK2, MYC2, TAG7, PYL1, and other genes related to indole-3-acetic acid and abscisic acid signal transduction and plant-pathogen interaction were up-regulated or down-regulated in both omics. We also used weighted gene co-expression network analysis to combine physiological and biochemical data (superoxide dismutase and catalase activity changes) with transcriptome and proteome data and finally identified three hub genes/proteins (SAG113, SRK2A, and ABCB1) that play an important role in plant hormone signal transduction. This work was the first study of gene/protein changes in resistant and susceptible mango varieties, and its results improved our understanding of the molecular mechanism of mango resistance to Xcm.

Cucumber abscisic acid 8'-hydroxylase Csyf2 regulates yellow flesh by modulating carotenoid biosynthesis.

Cucumber (Cucumis sativus L.) flesh is typically colorless or pale green. Flesh with yellow or orange pigment, determined mainly by carotenoid content and composition, is mostly found in semi-wild Xishuangbanna cucumber, which has a very narrow genetic background. Here, we identified a spontaneous cucumber mutant with yellow flesh (yf-343), which accumulated more β-cryptoxanthin and less lutein than regular cultivated European glasshouse-type cucumbers. Genetic analysis revealed that the yellow flesh phenotype was controlled by a single recessive gene. Through fine mapping and gene sequencing, we identified the candidate gene C. sativus yellow flesh 2 (Csyf2), encoding an abscisic acid (ABA) 8'-hydroxylase. Overexpression and RNAi-silencing of Csyf2 in cucumber hairy roots produced lower and higher ABA contents than in non-transgenic controls, respectively. Further, RNA-seq analysis suggested that genes related to ABA signal transduction were differentially expressed in fruit flesh between yf-343 and its wild type, BY, with white flesh. The carotenoid biosynthesis pathway was specifically enriched in fruit flesh at 30 days after pollination when yf-343 fruit flesh turns yellow. Our findings highlight a promising target for gene editing to increase carotenoid content, expanding our genetic resources for pigmented cucumber flesh breeding for improving the nutritional quality of cucumber.

The ABI3-ERF1 module mediates ABA-auxin crosstalk to regulate lateral root emergence

Abscisic acid (ABA) is involved in lateral root (LR) development, but how ABA signaling interacts withauxin signaling to regulate LR formation is not well understood. Here, we report that ABA-responsive ERF1 mediates the crosstalk between ABA and auxin signaling to regulate Arabidopsis LR emergence. ABI3 is a negative factor in LR emergence and transcriptionally activates ERF1 by binding to its promoter, and reciprocally, ERF1 activates ABI3, which forms a regulatory loop that enables rapid signal amplification. Notably, ABI3 physically interacts with ERF1, reducing the cis element-binding activities of bothERF1 and ABI3 and thus attenuating the expression of ERF1-/ABI3-regulated genes involved inLR emergence and ABA signaling, such as PIN1, AUX1, ARF7, and ABI5, which may provide a molecular rheostat to avoid overamplification of auxin and ABA signaling. Taken together, our findings identify the role of the ABI3-ERF1 module in mediating crosstalk between ABA and auxin signaling in LR emergence.

ABA Biosynthesis- and Signaling-Related Gene Expression Differences between Sweet Cherry Fruits Suggest Attenuation of ABA Pathway in Bicolored Cultivars.

Fruit development involves exocarp color evolution. However, signals that control this process are still elusive. Differences between dark-red and bicolored sweet cherry cultivars rely on MYB factor gene mutations. Color evolution in bicolored fruits only occurs on the face receiving sunlight, suggesting the perception or response to color-inducing signals is affected. These color differences may be related to synthesis, perception or response to abscisic acid (ABA), a phytohormone responsible for non-climacteric fruit coloring. This work aimed to determine the involvement of ABA in the coloring process of color-contrasting varieties. Several phenolic accumulation patterns differed between bicolored 'Royal Rainier' and dark-red 'Lapins'. Transcript abundance of ABA biosynthetic genes (PavPSY, PavZEP and PavNCED1) decreased dramatically from the Pink to Red stage in 'Royal Rainier' but increased in 'Lapins', which correlated with a higher ABA content in this dark-red cultivar. Transcripts coding for ABA signaling (PavPP2Cs, PavSnRKs and PavMYB44.1) were almost undetectable at the Red stage in 'Royal Rainier'. Field trials revealed that 'Royal Rainier' color development was insensitive to exogenous ABA, whereas it increased in 'Lapins'. Furthermore, ABA treatment only increased transcript levels of signaling genes in 'Lapins'. Further studies may address if the ABA pathway is attenuated in bicolor cultivars.

Constitutive expression of nucleotide-binding and leucine-rich repeat gene AtRPS2 enhanced drought and salt tolerance in rice

Drought and salt are major abiotic stresses that severely restricts plant growth and development, leading to serious losses in agricultural production. Therefore, improving crop tolerance to drought and salt stresses is an urgent issue. A previous study showed that overexpression of Arabidopsis NLR gene AtRPS2 conferred broad-spectrum disease resistance in rice. In this study, we demonstrated that constitutive expression of AtRPS2 increased abscisic acid (ABA) sensitivity during seedling stage, the shoot length of transgenic plants were shorter than wild type plants. Exogenous application of ABA markedly induced the expression of stress-related genes and promoted stomatal close in transgenic plants. Overexpression of AtRPS2 also enhanced drought and salt tolerance in rice, transgenic plants exhibited higher survival rates under drought and salt conditions than wild type plants. The activities of catalase (CAT) and superoxide dismutase (SOD) were higher in AtRPS2 transgenic rice than wild type plants. In addition, the expression of stress-related genes and ABA-responsive genes were significantly upregulated in AtRPS2 transgenic plants than wild type plants under drought and salt treatments. Besides, exogenous application of ABA could facilitate drought and salt tolerance in AtRPS2 transgenic plants. Taken together, this study indicated that AtRPS2 could improve drought and salt tolerance in rice, and this phenomenon is likely to be regulated through ABA signaling pathways.

PROTEIN PHOSPHATASE 2C08, a Negative Regulator of Abscisic Acid Signaling, Promotes Internode Elongation in Rice

Clade A protein phosphatase 2Cs (PP2CAs) negatively regulate abscisic acid (ABA) signaling. Here, we investigated the functions of OsPP2CAs and their crosstalk with ABA and gibberellic acid (GA) signaling pathways in rice (Oryza sativa). Among the nine OsPP2CAs, OsPP2C08 had the highest amino acid sequence similarity with OsPP2C51, which positively regulates GA signaling in rice seed germination. However, OsPP2C08 was expressed in different tissues (internodes, sheaths, and flowers) compared to OsPP2C51, which was specifically expressed in seeds, and showed much stronger induction under abiotic stress than OsPP2C51. Transgenic rice lines overexpressing OsPP2C08 (OsPP2C08-OX) had a typical ABA-insensitive phenotype in a post-germination assay, indicating that OsPP2C08, as with other OsPP2CAs, negatively regulates ABA signaling. Furthermore, OsPP2C08-OX lines had longer stems than wild-type (WT) plants due to longer internodes, especially between the second and third nodes. Internode cells were also longer in OsPP2C08-OX lines than in the WT. As GA positively regulates plant growth, these results suggest that OsPP2C08 might positively regulate GA biosynthesis. Indeed, the expression levels of GA biosynthetic genes including gibberellin 20-oxidase (OsGA20ox4) and Ent-kaurenoic acid oxidase (OsKAO) were increased in OsPP2C08-OX lines, and we observed that GIBBERELLIN 2-OXIDASE 4 (OsGA2ox4), encoding an oxidase that catalyzes the 2-beta-hydroxylation of several biologically active GAs, was repressed in the OsPP2C08-OX lines based on a transcriptome deep sequencing and RT-qPCR analysis. Furthermore, we compared the accumulation of SLENDER RICE 1 (SLR1), a DELLA protein involved in GA signaling, in OsPP2C08-OX and WT plants, and observed lower levels of SLR1 in the OsPP2C08-OX lines than in the WT. Taken together, our results reveal that OsPP2C08 negatively regulates ABA signaling and positively regulates GA signaling in rice. Our study provides valuable insight into the molecular mechanisms underlying the crosstalk between GA and ABA signaling in rice.

Genome-wide identification of the PYL gene family of tea plants (Camellia sinensis) revealed its expression profiles under different stress and tissues

BackgroundPYL (Pyrabactin resistance 1-like) protein is a receptor of abscisic acid (ABA), which plays an important role in ABA signaling and influences plant growth and development and stress response. However, studies on PYL gene family in tea plants have not been reported.ResultsIn this study, we identified 20 PYL genes from the reference genome of tea plant (‘Shuchazao’). Phylogeny analysis indicated that PYLs from tea and other plant species were clustered into seven groups. The promoter region of PYL genes contains a large number of cis-elements related to hormones and stresses. A large number of PYL genes responding to stress were found by analyzing the expression levels of abiotic stress and biotic stress transcriptome data. For example, CSS0047272.1 were up-regulated by drought stress, and CSS0027597.1 could respond to both anthracnose disease and geometrid feeding treatments. In addition, 10 PYL genes related to growth and development were verified by RT-qPCR and their tissue expression characteristics were revealed.ConclusionsOur results provided a comprehensive characteristic of the PYL gene family in tea plants and provided an important clue for further exploring its functions in the growth and development, and resistance to stress of tea plants.

Transcription factor RcNAC091 enhances rose drought tolerance through the abscisic acid-dependent pathway.

NAC (NAM, ATAF1,2, and CUC2) transcription factors (TFs) play critical roles in controlling plant growth, development, and abiotic stress responses. However, few studies have examined NAC proteins related to drought stress tolerance in rose (Rosa chinensis). Here, we identified a drought- and abscisic acid (ABA)-induced NAC TF, RcNAC091, that localizes to the nucleus and has transcriptional activation activity. Virus-induced silencing of RcNAC091 resulted in decreased drought stress tolerance, and RcNAC091 overexpression had the opposite effect. Specifically, ABA mediated RcNAC091-regulated drought tolerance. A transcriptomic comparison showed altered expression of genes involved in ABA signaling and oxidase metabolism in RcNAC091-silenced plants. We further confirmed that RcNAC091 directly targets the promoter of RcWRKY71 in vivo and in vitro. Moreover, RcWRKY71-slienced rose plants were not sensitive to both ABA and drought stress, whereas RcWRKY71-overexpressing plants were hypersensitive to ABA, which resulted in drought-tolerant phenotypes. The expression of ABA biosynthesis- and signaling-related genes was impaired in RcWRKY71-slienced plants, suggesting that RcWRKY71 might facilitate the ABA-dependent pathway. Therefore, our results show that RcWRKY71 is transcriptionally activated by RcNAC091, which positively modulates ABA signaling and drought responses. The results of this study provide insights into the roles of TFs as functional links between RcNAC091 and RcWRKY71 in priming resistance; our findings also have implications for the approaches to enhance the drought resistance of roses.

Transcriptomic Profiling Highlights the ABA Response Role of BnSIP1-1 in Brassica napus.

BnSIP1-1 is the first identified SIP1 (6b Interacting Protein1) subfamily gene of the trihelix transcription factor family from Brassica napus (B. napus). We previously used a reverse genetic method to reveal its abiotic stress response function in endowing plants resistance to drought and salinity, as well as ABA (Abscisic acid). However, the molecular mechanisms of BnSIP1-1 are unclear. In this study, the global transcriptome files of BnSIP1-1-overexpressing transgenic and wildtype B. napus seedlings under ABA treatment were constructed using RNA-seq. A total of 1823 and 5512 DEGs (Differentially Expressed Genes) were identified in OE vs. WT and OE_ABA vs. WT_ABA comparison groups, which included 751 and 2567 up-regulated DEGs, and 1072 and 2945 down-regulated DEGs, separately. The impact of overexpressed BnSIP1-1 on plants was amplified by ABA, indicating BnSIP1-1 was an ABA-conditioned responsive gene. More interestingly, we found the reasons for BnSIP1-1 increasing plants' insensitivity to ABA were not by regulating ABA synthesis and catabolism, but by manipulating ABA transportation, ABA signal perception and transduction, inositol phosphate metabolism, as well as endomembrane trafficking, indirectly suggesting this gene may play roles upstream of the core ABA response pathway. Our results provided new insights into improving the knowledge about the function of BnSIP1-1 and the ABA signaling mechanism in B. napus.

Next-generation ABACUS biosensors reveal cellular ABA dynamics driving root growth at low aerial humidity

The plant hormone abscisic acid (ABA) accumulates under abiotic stress to recast water relations and development. To overcome a lack of high-resolution sensitive reporters, we developed ABACUS2s—next-generation Förster resonance energy transfer (FRET) biosensors for ABA with high affinity, signal-to-noise ratio and orthogonality—that reveal endogenous ABA patterns in Arabidopsis thaliana. We mapped stress-induced ABA dynamics in high resolution to reveal the cellular basis for local and systemic ABA functions. At reduced foliar humidity, root cells accumulated ABA in the elongation zone, the site of phloem-transported ABA unloading. Phloem ABA and root ABA signalling were both essential to maintain root growth at low humidity. ABA coordinates a root response to foliar stresses, enabling plants to maintain foraging of deeper soil for water uptake.

BBX24 Increases Saline and Osmotic Tolerance through ABA Signaling in Arabidopsis Seeds.

Seed germination is a critical stage for survival during the life cycle of an individual plant. Genetic and environmental cues are integrated by individual seeds to determine germination, mainly achieved through regulation of the metabolism and signaling of gibberellins (GA) and abscisic acid (ABA), two phytohormones with antagonistic roles. Saline and drought conditions can arrest the germination of seeds and limit the seedling emergence and homogeneity of crops. This work aimed to study the function of BBX24, a B-Box transcription factor, in the control of germination of Arabidopsis thaliana seeds imbibed in saline and osmotic conditions. Seeds of mutant and reporter GUS lines of BBX24 were incubated at different doses of NaCl and polyethylene-glycol (PEG) solutions and with ABA, GA and their inhibitors to evaluate the rate of germination. We found that BBX24 promotes seed germination under moderated stresses. The expression of BBX24 is inhibited by NaCl and PEG. In addition, ABA suppresses BBX24-induced seed germination. Additional experiments suggest that BBX24 reduces ABA sensitivity, improving NaCl tolerance, and increases GA sensitivity in seeds imbibed in ABA. In addition, BBX24 inhibits the expression of ABI3 and ABI5 and genetically interacts upstream of HY5 and ABI5. This study demonstrates the relevance of BBX24 to induce drought and salinity tolerance in seed germination to ensure seedling emergence in sub-optimal environments.

Overexpression of 9-cis-Epoxycarotenoid Dioxygenase Gene, IbNCED1, Negatively Regulates Plant Height in Transgenic Sweet Potato.

Plant height is one of the key agronomic traits for improving the yield of sweet potato. Phytohormones, especially gibberellins (GAs), are crucial to regulate plant height. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) is the key enzyme for abscisic acid (ABA) biosynthesis signalling in higher plants. However, its role in regulating plant height has not been reported to date. Here, we cloned a new NCED gene, IbNCED1, from the sweet potato cultivar Jishu26. This gene encoded the 587-amino acid polypeptide containing an NCED superfamily domain. The expression level of IbNCED1 was highest in the stem and the old tissues in the in vitro-grown and field-grown Jishu26, respectively. The expression of IbNCED1 was induced by ABA and GA3. Overexpression of IbNCED1 promoted the accumulation of ABA and inhibited the content of active GA3 and plant height and affected the expression levels of genes involved in the GA metabolic pathway. Exogenous application of GA3 could rescue the dwarf phenotype. In conclusion, we suggest that IbNCED1 regulates plant height and development by controlling the ABA and GA signalling pathways in transgenic sweet potato.

ClSnRK2.3 negatively regulates watermelon fruit ripening and sugar accumulation.

Watermelon (Citrullus lanatus) as non-climacteric fruit is domesticated from the ancestors with inedible fruits. We previously revealed that the abscisic acid (ABA) signaling pathway gene ClSnRK2.3 might influence watermelon fruit ripening. However, the molecular mechanisms are unclear. Here, we found that the selective variation of ClSnRK2.3 resulted in lower promoter activity and gene expression level in cultivated watermelons than ancestors, which indicated ClSnRK2.3 might be a negative regulator in fruit ripening. Overexpression (OE) of ClSnRK2.3 significantly delayed watermelon fruit ripening and suppressed the accumulation of sucrose, ABA and gibberellin GA4 . Furthermore, we determined that the pyrophosphate-dependent phosphofructokinase (ClPFP1) in sugar metabolism pathway and GA biosynthesis enzyme GA20 oxidase (ClGA20ox) could be phosphorylated by ClSnRK2.3 and thereby resulting in accelerated protein degradation in OE lines and finally led to low levels of sucrose and GA4 . Besides that, ClSnRK2.3 phosphorylated homeodomain-leucine zipper protein (ClHAT1) and protected it from degradation to suppress the expression of the ABA biosynthesis gene 9'-cis-epoxycarotenoid dioxygenase 3 (ClNCED3). These results indicated that ClSnRK2.3 negatively regulated watermelon fruit ripening by manipulating the biosynthesis of sucrose, ABA and GA4 . Altogether, these findings revealed a novel regulatory mechanism in non-climacteric fruit development and ripening.

Arabidopsis EIN2 represses ABA responses during germination and early seedling growth by inactivating HLS1 protein independently of the canonical ethylene pathway.

The signaling pathways for the phytohormones ethylene and abscisic acid (ABA) have antagonistic effects on seed germination and early seedling establishment. However, the underlying molecular mechanisms remain unclear. In Arabidopsis thaliana, ETHYLENE INSENSITIVE 2 (EIN2) localizes to the endoplasmic reticulum (ER); although its biochemical function is unknown, it connects the ethylene signal with the key transcription factors EIN3 and EIN3-LIKE 1 (EIL1), leading to the transcriptional activation of ethylene-responsive genes. In this study, we uncovered an EIN3/EIL1-independent role for EIN2 in regulating the ABA response. Epistasis analysis demonstrated that this distinct role of EIN2 in the ABA response depends on HOOKLESS 1 (HLS1), the putative histone acetyltransferase acting as a positive regulator of ABA responses. Protein interaction assays supported a direct physical interaction between EIN2 and HLS1 in vitro and in vivo. Loss of EIN2 function resulted in an alteration of HLS1-mediated histone acetylation at the ABA-INSENSITIVE 3 (ABI3) and ABI5 loci, which promotes gene expression and the ABA response during seed germination and early seedling growth, indicating that the EIN2-HLS1 module contributes to ABA responses. Our study thus revealed that EIN2 modulates ABA responses by repressing HLS1 function, independently of the canonical ethylene pathway. These findings shed light on the intricate regulatory mechanisms underling the antagonistic interactionsbetween ethylene and ABA signaling, with significant implications for our understanding of plant growth and development.