Abscisic Acid Receptor Research Articles

Genome-wide identification of the ABA receptor PYL gene family and expression analysis in Prunus avium L.

The Pyrabactin resistance 1-like proteins (PYR/PYL/RCAR) are components of the ABA signaling pathway, playing a key role in how plants respond to abiotic stresses. Although PYL genes have been identified in a variety of plants, the evolution and structural characteristics of these genes in sweet cherry (Prunus avium L.) trees are largely unknown. In this study, 11 PaPYL genes were identified at genome-wide level in sweet cherry and were mapped to six chromosomes. According to the phylogenetic analysis, this gene family consisted of four subgroups; genes in the same subgroup had similar conserved motifs and the same number of exons, as revealed by analyzing gene structure. The intra-species collinearity analysis did not find any tandem duplication events in this gene family, and thus fragment duplication may be the primary reason for the generation of some PaPYL genes. Additionally, the inter-species collinearity analysis uncovered a potential evolutionary relationship between them. The expression analysis indicated that some PaPYL genes are specifically expressed in tissues, suggesting they may have unique functions. We also explored the expression of this gene family under different abiotic stress treatments (cold, salinity, drought). The qRT-PCR results showed that the expression levels of most genes were up-regulated under abiotic stress treatments, consistent with the results for their analyzed promoter cis-acting elements. This study provides a basis for further elucidating the function and expression patterning of the PYL gene family in sweet cherry, and helps to further analyze its regulatory mechanism under various abiotic stress factors.

Integrative analysis of transcriptome and metabolome revealed the mechanisms by which flavonoids and phytohormones regulated the adaptation of alfalfa roots to NaCl stress.

Salinity critically affects the growth and development of alfalfa (Medicago sativa), making it necessary to understand the molecular mechanism of alfalfa's adaptation to salt stress. In this study, alfalfa roots were subjected to salt stress and transcriptomics and metabolomics analyses were performed. The results showed that flavonoid synthesis, hormone synthesis, and transduction pathways may be involved in the alfalfa salt stress adaptation reaction, and that they are related. Combined analysis of differential genes and differential metabolites found that dihydroquercetin and beta-ring hydroxylase (LUT5), ABA responsive element binding factor 2 (ABF2), protein phosphatase PP2C (PP2C) and abscisic acid (ABA) receptor PYL2 (PYL), luteolinidin was significantly correlated with PP2C and phytochrome-interacting factor 4 (PIF4) and (+)-7-isomethyl jasmonate were significantly correlated with flavonol synthase (FLS) gene. (+)-7-isomethyl jasmonate and homoeriodictyol chalcone were significantly correlated with peroxidase (POD). POD was significantly up-regulated under NaCl stress for 6 and 24 h. Moreover, flavonoids, gibberellin (GA), jasmonic acid (JA) and ABA were suggested to play an important role in alfalfa's response to salt stress. Further, GA,ABA, and JA may be involved in the regulation of flavonoids to improve alfalfa's salt tolerance, and JA may be a key signal to promote the synthesis of flavonoids. This study revealed the possible molecular mechanism of alfalfa adaptation to salt stress, and identified a number of salt-tolerance candidate genes from the synthesis and signal transduction pathways of flavonoids and plant hormones, providing new insights into the regulatory network of alfalfa response to salt stress.

Abscisic acid agonists suitable for optimizing plant water use.

Climate change and overexploitation of groundwater resources cause constraints on water demand for agriculture, thus threatening crop productivity. For future food security, there is an urgent need for crops of high water use efficiency combined with high crop productivity, i.e. having high water productivity. Highwater productivity means efficient biomass accumulation at reduced transpiration. Recent studies show that plants are able to optimize carbon uptake per water transpired with little or no trade-off in yield. The phytohormone abscisic acid (ABA) plays a pivotal role in minimizing leaf transpiration and mediating enhanced water productivity. Hence, ABA and more chemically stable ABA agonists have the potential to improve crop water productivity. Synthesis, screening, and identification of suitable ABA agonists are major efforts currently undertaken. In this study, we used yeast expressing the plant ABA signal pathway to prescreen ABA-related cyano cyclopropyl compounds (CCPs). The yeast analysis allowed testing the ABA agonists for general toxicity, efficient uptake, and specificity in regulating different ABA receptor complexes. Subsequently, promising ABA-mimics were analyzed in vitro for ligand-receptor interaction complemented by physiological analyses. Several CCPs activated ABA signaling in yeast and plant cells. CCP1, CCP2, and CCP5 were by an order of magnitude more efficient than ABA in minimizing transpiration of Arabidopsis plants. In a progressive drought experiment, CCP2 mediated an increase in water use efficiency superior to ABA without trade-offs in biomass accumulation.

Relationship analysis of FaPYR1 and FaCHS genes encoding fruit ripening of three species of strawberries (Fragaria spp.) fruit

Abstract. Aristya GR, Dyatama GR, Zuyyina C, Maulina NTA, Arif MF, Musthofa A, Kasiamdari RS. 2023. Relationship analysis of FaPYR1 and FaCHS genes encoding fruit ripening of three species of strawberries (Fragaria spp.) fruit. Biodiversitas 24: 87-97. The difference in the phenotypes characters and gene expressionof strawberries (Fragaria spp.) is influenced by changes in hormone signaling mechanisms to receptors due to the adaptation to various types of environments. Abscisic acid (ABA) is one of the phytohormones that plays a role in the growth and development of strawberries, response to environmental stress, and fruit ripening. One of the ABA receptors is the PYR1 protein which is encoded by FaPYR1 gene. ABA also plays a role in inducing the FaCHS gene associated with pigmentation in strawberry fruit. This study aimed to analyze the relationship between FaPYR1 and FaCHS gene sequences in three strawberry species encoding fruit ripening. The FaPYR1 (585-633 bp) and FaCHS (90-93 bp) genes from three strawberries species namely Fragaria moschata, Fragaria vesca L. 'Californica', and Fragariax ananassa 'Festival' were successfully amplified. The results of the gene family relationship analysis of FaPYR1 gene sequences showed a close relationship with the comparative three species to GenBank, with a genetic distance value of 0.01-0.02. Meanwhile, FaCHS gene sequences from three species of strawberries showed a close relationship with the comparable FaCHS gene sequence from GenBank, with a genetic distance of 0.1-0.2.

A Medicago truncatula lncRNA MtCIR1 negatively regulates response to salt stress.

A lncRNA MtCIR1 negatively regulates the response to salt stress in Medicago truncatula seed germination by modulating seedling growth and ABA metabolism and signaling by enhancing Na+ accumulation. Increasing evidence suggests that long non-coding RNAs (lncRNAs) are involved in the regulation of plant tolerance to varying abiotic stresses. A large number of lncRNAs that are responsive to abiotic stress have been identified in plants; however, the mechanisms underlying the regulation of plant responses to abiotic stress by lncRNAs are largely unclear. Here, we functionally characterized a salt stress-responsive lncRNA derived from the leguminous model plant M. truncatula, referred to as MtCIR1, by expressing MtCIR1 in Arabidopsis thaliana in which no such homologous sequence was observed. Expression of MtCIR1 rendered seed germination more sensitive to salt stress by enhanced accumulation of abscisic acid (ABA) due to suppressing the expression of the ABA catabolic enzyme CYP707A2. Expression of MtCIR1 also suppressed the expression of genes associated with ABA receptors and signaling. The ABA-responsive gene AtPGIP2 that was involved in degradation of cell wall during seed germination was up-regulated by expressing MtCIR1. On the other hand, expression of MtCIR1 in Arabidopsisthaliana enhanced foliar Na+ accumulation by down-regulating genes encoding Na+ transporters, thus rendering the transgenic plants more sensitive to salt stress. These results demonstrate that the M. truncatula lncRNA MtCIR1 negatively regulates salt stress response by targeting ABA metabolism and signaling during seed germination and foliar Na+ accumulation by affecting Na+ transport under salt stress during seedling growth. Thesenovel findings would advance our knowledge on the regulatory roles of lncRNAs in response of plants to salt stress.

Identification and Expression Analysis of Abscisic Acid Signal Transduction Genes in Hemp Seeds

Abscisic acid (ABA) is involved in regulating diverse biological processes, but its signal transduction genes and roles in hemp seed germination are not well known. Here, the ABA signaling pathway members, <i>PYL</i>, <i>PP2C</i> and <i>SnRK2</i> gene families, were identified from the hemp reference genome, including 7 <i>CsPYL</i> (pyrab-actin resistance1-like, ABA receptor), 8 <i>CsPP2CA</i> (group A protein phosphatase 2c), and 7 <i>CsSnRK2</i> (sucrose nonfermenting1-related protein kinase 2). The content of ABA in hemp seeds in germination stage is lower than that in non-germination stage. Exogenous ABA (1 or 10 μM) treatment had a significant regulatory effect on the selected <i>PYL</i>, <i>PP2C</i>, <i>SnRK2</i> gene families. <i>CsAHG3</i> and <i>CsHAI1</i> were most significantly affected by exogenous ABA treatment. Yeast two-hybrid experiments were performed to reveal that CsPYL5, CsSnRK2.2, and CsSnRK2.3 could interact with CsPP2CA7 and demonstrate that this interaction was ABA-independent. Our results indicated that <i>CsPYL5</i>, <i>CsSnRK2.2</i>, <i>CsSnRK2.3</i> and <i>CsPP2CA7</i> might involve in the ABA signaling transduction pathway of hemp seeds during the hemp seed germination stages. This study suggested that novel genetic views can be brought into investigation of ABA signaling pathway in hemp seeds and lay the foundation for further exploration of the mechanism of hemp seed germination.

Genome-wide identification of the PYL gene family and expression of PYL genes under abiotic stresses in Chinese cabbage

The family of pyrabactin resistance 1 (PYR1)/PYR1-like (PYL) regulatory components of ABA receptors (RCAR) play a vital role in the initial step of ABA signaling. To understand the expression mode of PYL genes in response to various abiotic stresses in Chinese cabbage (Brassica rapa ssp. pekinensis), the members of BrPYL gene family were first identified with the relevant bioinformatics software. And then, the relative expressions of identified BrPYLs after heat, cold, drought, and salt treatments for 0, 24, 48, and 72 h were determined via real-time quantitative PCR. Here, we identified 24 PYLs in the B. rapa genome. Based on the phylogenetic analysis, these BrPYL genes were divided into three classes and distributed on ten chromosomes in Chinese cabbage. Most of BrPYL genes in the same group have similar gene structures and intron numbers. There were seven genes (BrPYL5, BrPYL8, BrPYL22, BrPYL3, BrPYL18, BrPYL11, and BrPYL21) from Group A with two introns and one gene (BrPYL19) from Group D with one intron. Analysis of conserved motifs suggested that every group contained motif 2 containing the Polyketide_cyc2 domain. Subsequently, the prediction of cis-acting elements indicated that BrPYL genes had 5 stress-related elements and 5 hormone-related elements, among which the number of MYC (dehydration reaction) was the highest, suggesting that BrPYL genes could respond to hormones and abiotic stresses. Expression patterns under four abiotic stresses showed that the expressions of BrPYL4, BrPYL11, BrPYL21, and BrPYL23 responded to these stresses at different time points. To conclude, we identified the BrPYL genes and build the BrPYLs expression mode in response to various abiotic stresses. This study provides a theoretical basis for stress-resistance breeding of Chinese cabbage.

CRISPR/Cas9-Mediated Multiple Knockouts in Abscisic Acid Receptor Genes Reduced the Sensitivity to ABA during Soybean Seed Germination.

Abscisic acid (ABA) is an important plant hormone that regulates numerous functions in plant growth, development, and stress responses. Several proteins regulate the ABA signal transduction mechanism in response to environmental stress. Among them, the PYR1/PYL/RCAR family act as ABA receptors. This study used the CRISPR/Cas9 gene-editing system with a single gRNA to knock out three soybean PYL genes: GmPYL17, GmPYL18, and GmPYL19. The gRNA may efficiently cause varying degrees of deletion of GmPYL17, GmPYL18, and GmPYL19 gene target sequences, according to the genotyping results of T0 plants. A subset of induced alleles was successfully transferred to progeny. In the T2 generation, we obtained double and triple mutant genotypes. At the seed germination stage, CRISPR/Cas9-created GmPYL gene knockout mutants, particularly gmpyl17/19 double mutants, are less susceptible to ABA than the wild type. RNA-Seq was used to investigate the differentially expressed genes related to the ABA response from germinated seedlings under diverse treatments using three biological replicates. The gmpyl17/19-1 double mutant was less susceptible to ABA during seed germination, and mutant plant height and branch number were higher than the wild type. Under ABA stress, the GO enrichment analysis showed that certain positive germination regulators were activated, which reduced ABA sensitivity and enhanced seed germination. This research gives a theoretical basis for a better understanding of the ABA signaling pathway and the participation of the key component at their molecular level, which helps enhance soybean abiotic stress tolerance. Furthermore, this research will aid breeders in regulating and improving soybean production and quality under various stress conditions.

Overexpressing OsPYL/RCAR7 Improves Drought Tolerance of Maize Seedlings by Reducing Stomatal Conductance

Drought stress is a serious abiotic factor limiting the quality and yield of maize (Zea mays). To produce maize plants with enhanced drought tolerance, we generated transgenic maize plants overexpressing OsPYL/RCAR7, encoding an abscisic acid receptor. We crossed the selected lines with maize variety B73 and obtained F1 hybrid seeds. Initial screening suggested that the transgenic lines were more drought tolerant than wild-type plants. Analysis using the DroughtSpotter platform indicated that expressing OsPYL/RCAR7 enhanced drought resistance in transgenic maize seedlings by reducing water loss. In addition, the stomatal conductance of the leaf surface was 30% lower in OsPYL/RCAR7-overexpressing plants than in wild-type ones. After drought treatment, OsPYL/RCAR7-overexpressing maize showed a much higher survival rate than the wild type, suggesting that expressing OsPYL/RCAR7 reduced the negative effects of drought exposure on stomatal conductance and enhanced water use efficiency. Furthermore, the expression levels of drought-tolerance–related abscisic acid–signaling genes ABP2 and RAB16A were higher in the transgenic plants than in the wild type. Taken together, our data indicate that the seedlings of transgenic maize expressing the gene OsPYL/RCAR7 showed increased tolerance to drought stress, raising the possibility that stress-related genes from monocotyledonous crops could be used as genetic resources to improve the agricultural traits of maize.

A regulatory loop establishes the link between the circadian clock and abscisic acid signaling in rice.

There is a close regulatory relationship between the circadian clock and the abscisic acid (ABA) signaling pathway in regulating many developmental processes and stress responses. However, the exact feedback regulation mechanism between them is still poorly understood. Here, we identified the rice (Oryza sativa) clock component PSEUDO-RESPONSE REGULATOR 95 (OsPRR95) as a transcriptional regulator that accelerates seed germination and seedling growth by inhibiting ABA signaling. We also found that OsPRR95 binds to the ABA receptor gene REGULATORY COMPONENTS OF ABA RECEPTORS10 (OsRCAR10) DNA and inhibits its expression. Genetic analysis showed OsRCAR10 acts downstream of OsPRR95 in mediating ABA responses. In addition, the induction of OsPRR95 by ABA partly required a functional OsRCAR10, and the ABA-responsive element-binding factor ABSCISIC ACID INSENSITIVE5 (OsABI5) bound directly to the promoter of OsPRR95 and activated its expression, thus establishing a regulatory feedback loop between OsPRR95, OsRCAR10, and OsABI5. Taken together, our results demonstrated that the OsRCAR10-OsABI5-OsPRR95 feedback loop modulates ABA signaling to fine-tune seed germination and seedling growth, thus establishing the molecular link between ABA signaling and the circadian clock.

Signaling Transduction of ABA, ROS, and Ca2+ in Plant Stomatal Closure in Response to Drought

Drought is a global threat that affects agricultural production. Plants have evolved several adaptive strategies to cope with drought. Stomata are essential structures for plants to control water status and photosynthesis rate. Stomatal closure is an efficient way for plants to reduce water loss and improve survivability under drought conditions. The opening and closure of stomata depend on the turgor pressure in guard cells. Three key signaling molecules, including abscisic acid (ABA), reactive oxygen species (ROS), and calcium ion (Ca2+), play pivotal roles in controlling stomatal closure. Plants sense the water-deficit signal mainly via leaves and roots. On the one hand, ABA is actively synthesized in root and leaf vascular tissues and transported to guard cells. On the other hand, the roots sense the water-deficit signal and synthesize CLAVATA3/EMBRYO-SURROUNDING REGION RELATED 25 (CLE25) peptide, which is transported to the guard cells to promote ABA synthesis. ABA is perceived by pyrabactin resistance (PYR)/PYR1-like (PYL)/regulatory components of ABA receptor (RCAR) receptors, which inactivate PP2C, resulting in activating the protein kinases SnRK2s. Many proteins regulating stomatal closure are activated by SnRK2s via protein phosphorylation. ABA-activated SnRK2s promote apoplastic ROS production outside of guard cells and transportation into the guard cells. The apoplastic H2O2 can be directly sensed by a receptor kinase, HYDROGEN PEROXIDE-INDUCED CA2+ INCREASES1 (HPCA1), which induces activation of Ca2+ channels in the cytomembrane of guard cells, and triggers an increase in Ca2+ in the cytoplasm of guard cells, resulting in stomatal closure. In this review, we focused on discussing the signaling transduction of ABA, ROS, and Ca2+ in controlling stomatal closure in response to drought. Many critical genes are identified to have a function in stomatal closure under drought conditions. The identified genes in the process can serve as candidate genes for genetic engineering to improve drought resistance in crops. The review summarizes the recent advances and provides new insights into the signaling regulation of stomatal closure in response to water-deficit stress and new clues on the improvement of drought resistance in crops.

A Novel R2R3-MYB Transcription Factor FtMYB22 Negatively Regulates Salt and Drought Stress through ABA-Dependent Pathway.

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is a coarse cereal with strongly abiotic resistance. The MYB family plays a regulatory role in plant growth, development, and responses to biotic and abiotic stresses. However, the characteristics and regulatory mechanisms of MYB transcription factors in Tartary buckwheat remain unclarified. Here, this study cloned the FtMYB22 gene from Tartary buckwheat, and investigated its involvement in responding to individual water deficit and salt stress in Arabidopsis. Sequence analysis highlighted that the N-termini of FtMYB22 contained two highly conserved SANT domains and one conserved domain from the SG20 subfamily. Nucleus-localized FtMYB22 did not have individual transcriptional activation activity. Water deficiency and salt stress induced the high expression of the GUS gene, which was driven by the promoter of FtMYB22. Yeast stress experiments showed that the overexpression of FtMYB22 significantly reduced the growth activity of transgenic yeast under water deficit or salt stress. Consistently, the overexpression of FtMYB22 reduced the salt and water deficit stress resistance of the transgenic plants. In addition, physiological parameters showed that transgenic plants had lower proline and antioxidant enzyme activity under stress conditions. Compared to the wild-type (WT), transgenic plants accumulated more malondialdehyde (MDA), H2O2, and O2−; they also showed higher ion permeability and water loss rates of detached leaves under stress treatments. Notably, FtMYB22 was involved in plant stress resistance through an ABA-dependent pathway. Under stress conditions, the expression of RD29A, RD29B, PP2CA, KIN1, COR15A, and other genes in response to plant stress in transgenic lines was significantly lower than that in the WT (p < 0.05). Furthermore, yeast two-hybrid assay showed that there was a significant interaction between FtMYB22 and the ABA receptor protein RCAR1/2, which functioned in the ABA signal pathway. Altogether, FtMYB22, as a negative regulator, inhibited a variety of physiological and biochemical reactions, affected gene expression and stomatal closure in transgenic plants through the ABA-dependent pathway, and reduced the tolerance of transgenic Arabidopsis to water deficiency and salt stress. Based on these fundamental verifications, further studies would shed light on the hormone signal response mechanism of FtMYB22.

Enhanced Resistance to Sclerotinia sclerotiorum in Brassica rapa by Activating Host Immunity through Exogenous Verticillium dahliae Aspf2-like Protein (VDAL) Treatment.

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most destructive diseases in Brassica rapa. Verticillium dahliae Aspf2-like protein (VDAL) is a secretory protein of V. dahliae which has been shown to enhance the resistance against fungal infections in several plants. Nonetheless, the molecular mechanisms of VDAL-primed disease resistance are still poorly understood. In this study, we performed physiological, biochemical, and transcriptomic analyses of Brassica rapa in order to understand how VDAL confers resistance to S. sclerotiorumn infections in plants. The results showed that foliar application of VDAL significantly reduced the plaque area on leaves inoculated with S. sclerotiorum. It also enhanced antioxidant capacity by increasing activities of superoxide dismutase (SOD), peroxidase (POD), peroxidase (APX), glutathione reductase (GR), protoporphyrinogen oxidase (PPO), and defense-related enzymes β-1,3-glucanase and chitinase during the infection periods. This occurred in parallel with significantly reduced relative conductivity at different periods and lower malondialdehyde (MDA) content as compared to sole S. sclerotiorum inoculation. Transcriptomic analysis showed a total of 146 (81 up-regulated and 65 down-regulated) differentially expressed genes (DEGs) in VDAL-treated leaves compared to the control. The most enriched three Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were the mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, and plant-pathogen interaction, all of which were associated with plant immunity. DEGs associated with MAPK and hormone signal transduction pathways were ethylene response sensor ERS2, EIN3 (Ethylene Insensitive3)-binding F-box protein 2 (EBF2), ethylene-responsive transcription factor ERF94, MAPK 9 (MKK9), protein phosphatase 2C (PP2C37), auxin-responsive proteins (AUX/IAA1 and 19), serine/threonine-protein kinase CTR1, and abscisic acid receptors (PLY 4 and 5). Among the DEGs linked with the plant-pathogen interaction pathway were calmodulin-like proteins (CML5, 24, 27), PTI1-like tyrosine protein kinase 3 (Pti13) and transcription factor MYB30, all of which are known to play key roles in pathogen-associated molecular pattern (PAMP)-triggered immunity and effector-triggered immunity (ETI) for hypersensitive response (HR), cell wall reinforcement, and stomatal closure in plants. Overall, VDLA treatment triggered repression of the auxin and ABA signaling pathways and de-repression of the ethylene signaling pathways in young B. rapa seedlings to increase plant innate immunity. Our results showed that VDAL holds great potential to enhance fungal disease resistance in B. rapa crop.

Characterization and expression analysis of key abscisic acid signal transduction genes during kiwifruit development

To characterise the regulation of abscisic acid (ABA) signal transduction during fruit development and ripening, we investigated the key genes involved in the ABA signalling pathway in kiwifruit (Actinidia chinensis), including 18 AcPYLs genes encoding ABA receptors, 7 AcPP2Cs genes encoding type 2C protein phosphatases, and 7 AcSnRK2s genes encoding members of the SNF1-related protein kinases 2 family identified in the kiwifruit reference genome. AcPYLs, AcPP2Cs, and AcSnRK2s from kiwifruit are putative homologues of the corresponding Arabidopsis and tomato proteins. Phylogenetic analysis revealed that AcPYLs and AcSnRK2s clustered into three subfamilies. Transcript levels indicated that the expression pattern of AcNCED4 was consistent with the ABA content of the pulp during kiwifruit development. Furthermore, the ABA content of the axile placenta was higher than that of the sarcocarp in kiwi pulp, and the expression of most ABA signal transduction genes, including AcPYLs, AcPP2Cs, and AcSnRK2s, was more predominant in the axile placenta. Moreover, AcPP2C3 was localised in the nucleus and could interact with all AcPYLs and AcSnRK2s in an ABA-independent manner, as revealed by subcellular localisation and yeast two-hybrid assays. These findings enhance our understanding of ABA signal transduction genes in kiwis, and provide the necessary background for further exploration of the molecular mechanisms at play during kiwifruit development.

The cassava (Manihot-esculenta Crantz)'s nitrate transporter NPF4.5, expressed in seedling roots, involved in nitrate flux and osmotic stress

AtNPF4.5/AIT2, which was predicted to be a low-affinity transporter capable for nitrate uptake, was screened by ABA receptor complex in Arabidopsis ten years ago. However, the molecular and biochemical characterizations of AtNPF4.5 in plants remained largely unclear. In this study, the function of a plasma-membrane-localized and root-specifically-expressed gene MeNPF4.5 (Manihot-esculenta NITRATE TRANSPORTER 1 PTR FAMILY4.5), an ortholog of the Arabidopsis thaliana NPF4.5, was investigated in cassava roots as a nitrate efflux transporter on low nitrate medium and an influx transporter following exposure to high concentration of external nitrates. Moreover, RNA interference (RNAi) of MeNPF4.5 reduced the nitrate efflux capacity but the overexpressing cassava seedlings increased the ability of efflux from the elongation to the mature zone of root under low nitrate treatments. Besides, MeNPF4.5-RNAi expression reduced the nitrate influx capacity but enhanced nitrate absorption in parts of overexpressing plants from the meristem, elongation to mature zone of roots under high nitrate conditions. Furthermore, MeNPF4.5-RNAi seedlings survived owing to roots that could grow normally, but the MeNPF4.5-over-expressors showed adverse growth under 7% PEG6000 stress, suggesting that MeNPF4.5 negatively regulated the osmotic stress and was involved in nitrate flux through cassava seedlings.

ABA-insensitivity of alfalfa (Medicago sativa L.) during seed germination associated with plant drought tolerance

Abscisic acid (ABA) is a vital stress hormone of plants in coping with adverse environmental conditions, such as drought stress. Sensitivity of seed germination to exogenous ABA treatment could be linked to varied drought stress responses in different plant species. Polyploid and outcrossing nature of alfalfa makes it an extensive reservoir of genetic variation, and each single alfalfa seed may have a different genetic background. We speculate the alfalfa seeds resistant to exogenous ABA treatment during germination could lead to a strong plant drought tolerance. Here, we selected the alfalfa seedlings (S0–50) from seeds germinated under 50 μM ABA treatment. The S0–50 alfalfa plants showed more sensitivity in stomatal closure to exogenous ABA and PEG treatments, and also stronger drought tolerance than the plants of ABA-sensitive seeds during germination (S0–0). Leaf ABA content analysis indicated that the S0–50 plants had a higher ABA content in normal and under drought stress growth conditions than the S0–0 plants. The seeds of the S0–50 plants (S1–50) showed significantly higher germination percentage under 50 μM ABA treatment and had longer roots after 15% PEG6000 treatment than the segregated ABA-sensitive seeds (S1–0). We found a cytosol-nucleus dual-localized PPR protein gene MsSOAR1 was significantly highly expressed in the S0–50 than in the S0–0 plants. Overexpression of AtSOAR1 , a negative regulator in ABA-mediated seed germination inhibition in Arabidopsis and a homologous gene of MsSOAR1 , led to significantly improved drought tolerance, increased branch number and plant height, and reduced expression of the ABA receptor genes MsPYL5 and MsPYL6 of AtSOAR1 transgenic alfalfa plants (TGs) . The results suggest that ABA-insensitivity during seed germination is associated with the impaired ABA signaling transduction. Screening alfalfa seedlings during seed germination with exogenous ABA is a way to obtain drought tolerant alfalfa germplasm. • During vegetative stage, the ABA-insensitive ‘Zhongmu No.1’ alfalfa plants, during seeds germination, showed stronger drought tolerance. • Higher ABA content and higher expression of MsSOAR1 gene may contributed to improved drought tolerance of alfalfa plants. • Ectopic overexpression of AtSOAR1 significantly improved alfalfa drought tolerance. • Screening alfalfa seedlings during seed germination with exogenous ABA is a way to obtain drought tolerant alfalfa germplasm.

Membrane Proteomic Profiling of Soybean Leaf and Root Tissues Uncovers Salt-Stress-Responsive Membrane Proteins.

Cultivated soybean (Glycine max (L.)), the world's most important legume crop, has high-to-moderate salt sensitivity. Being the frontier for sensing and controlling solute transport, membrane proteins could be involved in cell signaling, osmoregulation, and stress-sensing mechanisms, but their roles in abiotic stresses are still largely unknown. By analyzing salt-induced membrane proteomic changes in the roots and leaves of salt-sensitive soybean cultivar (C08) seedlings germinated under NaCl, we detected 972 membrane proteins, with those present in both leaves and roots annotated as receptor kinases, calcium-sensing proteins, abscisic acid receptors, cation and anion channel proteins, proton pumps, amide and peptide transporters, and vesicle transport-related proteins etc. Endocytosis, linoleic acid metabolism, and fatty acid biosynthesis pathway-related proteins were enriched in roots whereas phagosome, spliceosome and soluble NSF attachment protein receptor (SNARE) interaction-related proteins were enriched in leaves. Using label-free quantitation, 129 differentially expressed membrane proteins were found in both tissues upon NaCl treatment. Additionally, the 140 NaCl-induced proteins identified in roots and 57 in leaves are vesicle-, mitochondrial-, and chloroplast-associated membrane proteins and those with functions related to ion transport, protein transport, ATP hydrolysis, protein folding, and receptor kinases, etc. Our proteomic results were verified against corresponding gene expression patterns from published C08 RNA-seq data, demonstrating the importance of solute transport and sensing in salt stress responses.

The IbPYL8-IbbHLH66-IbbHLH118 complex mediates the abscisic acid-dependent drought response in sweet potato.

Drought limits crop development and yields. bHLH (basic helix-loop-helix) transcription factors play critical roles in regulating the drought response in many plants, but their roles in this process in sweet potato are unknown. Here, we report that two bHLH proteins, IbbHLH118 and IbbHLH66, play opposite roles in the ABA-mediated drought response in sweet potato. ABA treatment repressed IbbHLH118 expression but induced IbbHLH66 expression in the drought-tolerant sweet potato line Xushu55-2. Overexpressing IbbHLH118 reduced drought tolerance, whereas overexpressing IbbHLH66 enhanced drought tolerance, in sweet potato. IbbHLH118 directly binds to the E-boxes in the promoters of ABA-insensitive 5 (IbABI5), ABA-responsive element binding factor 2 (IbABF2) and tonoplast intrinsic protein 1 (IbTIP1) to suppress their transcription. IbbHLH118 forms homodimers with itself or heterodimers with IbbHLH66. Both of the IbbHLHs interact with the ABA receptor IbPYL8. ABA accumulates under drought stress, promoting the formation of the IbPYL8-IbbHLH66-IbbHLH118 complex. This complex interferes with IbbHLH118's repression of ABA-responsive genes, thereby activating ABA responses and enhancing drought tolerance. These findings shed light on the role of the IbPYL8-IbbHLH66-IbbHLH118 complex in the ABA-dependent drought response of sweet potato and identify candidate genes for developing elite crop varieties with enhanced drought tolerance.

Transcriptome Analysis of Low-Temperature-Treated Tetraploid Yellow Actinidia chinensis Planch. Tissue Culture Plantlets.

Simple SummaryYellow kiwifruit (Actinidia chinensis Planch.) is popular in the market. However, it is highly susceptible to severe weather, including as low temperatures and frost, which may affect its production in the coming year. The cold-resistant mechanism of yellow kiwifruit associated with gene regulation is poorly investigated. To better understand cold-adaptive mechanisms, we grew plants under low-temperature conditions, which was followed by transcriptome analysis to discern the genes that play an active role in growth under low temperatures. The findings and dataset obtained in this study advance our knowledge of the cold-adaptive genes in regulatory networks and helps us to understand the cold-tolerance mechanisms in the tetraploid yellow kiwifruit.The cold-resistant mechanism of yellow kiwifruit associated with gene regulation is poorly investigated. In this study, to provide insight into the causes of differences in low-temperature tolerance and to better understand cold-adaptive mechanisms, we treated yellow tetraploid kiwifruit ‘SWFU03’ tissue culture plantlets at low temperatures, used these plantlets for transcriptome analysis, and validated the expression levels of ten selected genes by real-time quantitative polymerase chain reaction (RT-qPCR) analysis. A number of 1630 differentially expressed genes (DEGs) were identified, of which 619 pathway genes were up-regulated, and 1011 were down-regulated in the cold treatment group. The DEGs enriched in the cold tolerance-related pathways mainly included the plant hormone signal transduction and the starch and sucrose metabolism pathway. RT-qPCR analysis confirmed the expression levels of eight up-regulated genes in these pathways in the cold-resistant mutants. In this study, cold tolerance-related pathways (the plant hormone signal transduction and starch and sucrose metabolism pathway) and genes, e.g., CEY00_Acc03316 (abscisic acid receptor PYL), CEY00_Acc13130 (bZIP transcription factor), CEY00_Acc33627 (TIFY protein), CEY00_Acc26744 (alpha-trehalose-phosphate synthase), CEY00_Acc28966 (beta-amylase), CEY00_Acc16756 (trehalose phosphatase), and CEY00_Acc08918 (beta-amylase 4) were found.

Is ABA the exogenous vector of interplant drought cuing?

ABSTRACT We have recently demonstrated that root cuing from drought-stressed plants increased the survival time of neighboring plants under drought, which came at performance costs under benign conditions. The involvement of abscisic acid (ABA) was implicated from additional experiments in which interplant drought cuing was greatly diminished in ABA-deficient plants. Here, we tested the hypothesis that ABA is the exogenous vector of interplant drought cuing. Pisum sativum plants were grown in rows of three split-root plants. One of the roots of the first plant was subjected to either drought of benign conditions in one rooting vial, while its other root shared its rooting vial with one of the roots of an unstressed neighbor, which in turn shared its other rooting vial with an additional unstressed neighbor. One hour after subjecting one of the roots of the first plant to drought, ABA concentrations were 106% and 145% higher around its other root and the roots of its unstressed neighbor, compared to their respective unstressed controls; however, the absolute concentrations of ABA found in the rooting media were substantially low. The results may indicate that despite its involvement in interplant drought and the commonly observed exchange of ABA between drought-stressed plants and their rhizospheres, ABA is not directly involved in exogenous interplant drought cuing. However, previous studies have shown that even minute concentrations of ABA in the rhizosphere can prevent ABA leakage from roots and thus to significantly increase endogenous ABA levels. In addition, under drought conditions, plants tend to accumulate ABA, which could markedly increase internal ABA concentrations over time and ABA concentrations in close proximity to the root surface might be significantly greater than estimated from entire rooting volumes. Finally, phaseic acid, an ABA degradation product, is known to activate various ABA receptors, which could enhance plant drought tolerance. It is thus feasible that while the role of ABA is limited, its more stable degradation products could play a significant role in interplant drought cuing. Our preliminary findings call for an extensive investigation into the identity and modes of operation of the exogenous vectors of interplant drought cuing.