AREB1 is a transcription activator of novel ABRE-dependent ABA signaling that enhances drought stress tolerance in Arabidopsis

Revealing critical mechanisms in determining sorghum resistance to drought and salt using mRNA, small RNA and degradome sequencing

BACKGROUND

Plant growth and development are severely threatened by drought and salt stresses. Compared with structural genes, transcription factors (TFs) play more pivotal roles in plant growth and stress adaptation. However, the underlying mechanisms of sorghum adapting to drought and salt are insufficient, and systematic analysis of TFs in response to the above stresses is lacking.

RESULTS

In this study, TFs were identified in sorghum and model plants (Arabidopsis thaliana and rice), and gene number and conserved domain were compared between sorghum and model plants. According to syntenic analysis, the expansion of sorghum and rice TFs may be due to whole-genome duplications. Between sorghum and model plants TFs, specific conserved domains were identified and they may be related to functional diversification of TFs. Forty-five key genes in sorghum, including four TFs, were likely responsible for drought adaption based on differently expression analysis. MiR5072 and its target gene (Sobic.001G449600) may refer to the determination of sorghum drought resistance according to small RNA and degradome analysis. Six genes were associated with drought adaptation of sorghum based on weighted gene co-expression network analysis (WGCNA). Similarly, the core genes in response to salt were also characterized using the above methods. Finally, 15 candidate genes, particularly two TFs (Sobic.004G300300, HD-ZIP; Sobic.003G244100, bZIP), involved in combined drought and salt resistance of sorghum were identified.

CONCLUSIONS

In summary, the findings in this study help clarify the molecular mechanisms of sorghum responding to drought and salt. We identified candidate genes and provide important genetic resource for potential development of drought-tolerant and salt-tolerant sorghum plants.

Advances in membrane-tethered NAC transcription factors in plants

Transcription factors are central components in cell signal transduction networks and are critical regulators for gene expression. It is estimated that approximately 10% of all transcription factors are membrane-tethered. MTFs (membrane-bound transcription factors) are latent transcription factors that are inherently anchored in the cellular membrane in a dormant form. When plants encounter environmental stimuli, they will be released from the membrane by intramembrane proteases or by the ubiquitin proteasome pathway and then were translocated to the nucleus. The capacity to instantly activate dormant transcription factors is a critical strategy for modulating diverse cellular functions in response to external or internal signals, which provides an important transcriptional regulatory network in response to sudden stimulus and improves plant survival. NTLs (NTM1-like) are a small subset of NAC (NAM, ATAF1/2, CUC2) transcription factors, which contain a conserved NAC domain at the N-terminus and a transmembrane domain at the C-terminus. In the past two decades, several NTLs have been identified from several species, and most of them are involved in both development and stress response. In this review, we review the reports and findings on NTLs in plants and highlight the mechanism of their nuclear import as well as their functions in regulating plant growth and stress response.

Regulatory networks in plant responses to drought and cold stress

Drought and cold represent distinct types of abiotic stress, each initiating unique primary signaling pathways in response to dehydration and temperature changes, respectively. However, a convergence at the gene regulatory level is observed where a common set of stress-responsive genes is activated to mitigate the impacts of both stresses. In this review, we explore these intricate regulatory networks, illustrating how plants coordinate distinct stress signals into a collective transcriptional strategy. We delve into the molecular mechanisms of stress perception, stress signaling, and the activation of gene regulatory pathways, with a focus on insights gained from model species. By elucidating both the shared and distinct aspects of plant responses to drought and cold, we provide insight into the adaptive strategies of plants, paving the way for the engineering of stress-resilient crop varieties that can withstand a changing climate.

Role of Abscisic Acid, Reactive Oxygen Species, and Ca2+ Signaling in Hydrotropism-Drought Avoidance-Associated Response of Roots

Plant roots exert hydrotropism in response to moisture gradients to avoid drought stress. The regulatory mechanism underlying hydrotropism involves novel regulators such as MIZ1 and GNOM/MIZ2 as well as abscisic acid (ABA), reactive oxygen species (ROS), and Ca2+ signaling. ABA, ROS, and Ca2+ signaling are also involved in plant responses to drought stress. Although the mechanism of moisture gradient perception remains largely unknown, the sensory apparatus has been reported to reside in the root elongation zone rather than in the root cap. In Arabidopsis roots, hydrotropism is mediated by the action of MIZ1 and ABA in the cortex of the elongation zone, the accumulation of ROS at the root curvature, and the variation in the cytosolic Ca2+ concentration in the entire root tip including the root cap and stele of the elongation zone. Moreover, root exposure to moisture gradients has been proposed to cause asymmetric ABA distribution or Ca2+ signaling, leading to the induction of the hydrotropic response. A comprehensive and detailed analysis of hydrotropism regulators and their signaling network in relation to the tissues required for their function is apparently crucial for understanding the mechanisms unique to root hydrotropism. Here, referring to studies on plant responses to drought stress, we summarize the recent findings relating to the role of ABA, ROS, and Ca2+ signaling in hydrotropism, discuss their functional sites and plausible networks, and raise some questions that need to be answered in future studies.

A novel maize F-bZIP member, ZmbZIP76, functions as a positive regulator in ABA-mediated abiotic stress tolerance by binding to ACGT-containing elements

The group F-bZIP transcription factors (TFs) in Arabidopsis are involved in nutrient deficiency or salt stress responses. Nevertheless, our learning about the functions of group F-bZIP genes in maize remains limited. Here, we cloned a new F-bZIP gene (ZmbZIP76) from maize inbred line He344. The expression of ZmbZIP76 in maize was dramatically induced by high salt, osmotic stress and abscisic acid. Accordingly, overexpression of ZmbZIP76 increased tolerance of transgenic plants to salt and osmotic stress. In addition, ZmbZIP76 functions as a nuclear transcription factor and upregulates the expression of a range of abiotic stress-responsive genes by binding to the ACGT-containing elements, leading to enhanced reactive oxygen species (ROS) scavenging capability, increased abscisic acid level, proline content, and ratio of K+/Na+, reduced water loss rate, and membrane damage. These physiological changes caused by ZmbZIP76 ultimately enhanced tolerance of transgenic plants to salt and osmotic stress.

Identification of a sugarcane bacilliform virus promoter that is activated by drought stress in plants

Sugarcane (Saccharum spp.) is an important sugar and biofuel crop in the world. It is frequently subjected to drought stress, thus causing considerable economic losses. Transgenic technology is an effective breeding approach to improve sugarcane tolerance to drought using drought-inducible promoter(s) to activate drought-resistance gene(s). In this study, six different promoters were cloned from sugarcane bacilliform virus (SCBV) genotypes exhibiting high genetic diversity. In β-glucuronidase (GUS) assays, expression of one of these promoters (PSCBV-YZ2060) is similar to the one driven by the CaMV 35S promoter and >90% higher compared to the other cloned promoters and Ubi1. Three SCBV promoters (PSCBV-YZ2060, PSCBV-TX, and PSCBV-CHN2) function as drought-induced promoters in transgenic Arabidopsis plants. In Arabidopsis, GUS activity driven by promoter PSCBV-YZ2060 is also upregulated by abscisic acid (ABA) and is 2.2-5.5-fold higher when compared to the same activity of two plant native promoters (PScRD29A from sugarcane and PAtRD29A from Arabidopsis). Mutation analysis revealed that a putative promoter region 1 (PPR1) and two ABA response elements (ABREs) are required in promoter PSCBV-YZ2060 to confer drought stress response and ABA induction. Yeast one-hybrid and electrophoretic mobility shift assays uncovered that transcription factors ScbZIP72 from sugarcane and AREB1 from Arabidopsis bind with two ABREs of promoter PSCBV-YZ2060. After ABA treatment or drought stress, the expression levels of endogenous ScbZIP72 and heterologous GUS are significantly increased in PSCBV-YZ2060:GUS transgenic sugarcane plants. Consequently, promoter PSCBV-YZ2060 is a possible alternative promoter for genetic engineering of drought-resistant transgenic crops such as sugarcane.

Duplicated Copy Number Variant of the Maize 9-Lipoxygenase ZmLOX5 Improves 9,10-KODA-Mediated Resistance to Fall Armyworms

Extensive genome structure variations, such as copy number variations (CNVs) and presence/absence variations, are the basis for the remarkable genetic diversity of maize; however, the effect of CNVs on maize herbivory defense remains largely underexplored. Here, we report that the naturally occurring duplication of the maize 9-lipoxygenase gene ZmLOX5 leads to increased resistance of maize to herbivory by fall armyworms (FAWs). Previously, we showed that ZmLOX5-derived oxylipins are required for defense against chewing insect herbivores and identified several inbred lines, including Yu796, that contained duplicated CNVs of ZmLOX5, referred to as Yu796-2×LOX5. To test whether introgression of the Yu796-2×LOX5 locus into a herbivore-susceptible B73 background that contains a single ZmLOX5 gene is a feasible approach to increase resistance, we generated a series of near-isogenic lines that contained either two, one, or zero copies of the Yu796-2×LOX5 locus in the B73 background via six backcrosses (BC6). Droplet digital PCR (ddPCR) confirmed the successful introgression of the Yu796-2×LOX5 locus in B73. The resulting B73-2×LOX5 inbred line displayed increased resistance against FAW, associated with increased expression of ZmLOX5, increased wound-induced production of its primary oxylipin product, the α-ketol, 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (9,10-KODA), and the downstream defense hormones regulated by this molecule, 12-oxo-phytodienoic acid (12-OPDA) and abscisic acid (ABA). Surprisingly, wound-induced JA-Ile production was not increased in B73-2×LOX5, resulting from the increased JA catabolism. Furthermore, B73-2×LOX5 displayed reduced water loss in response to drought stress, likely due to increased ABA and 12-OPDA content. Taken together, this study revealed that the duplicated CNV of ZmLOX5 quantitively contributes to maize antiherbivore defense and presents proof-of-concept evidence that the introgression of naturally occurring duplicated CNVs of a defensive gene into productive but susceptible crop varieties is a feasible breeding approach for enhancing plant resistance to herbivory and tolerance to abiotic stress.

Potential Response Patterns of Endogenous Hormones in Cliff Species Opisthopappus taihangensis and Opisthopappus longilobus under Salt Stress

When plants are exposed to salt stress, endogenous hormones are essential for their responses through biosynthesis and signal transduction pathways. However, the roles of endogenous hormones in two cliff species (Opisthopappus taihangensis and Opisthopappus longilobus (Opisthopappus genus)) in the Taihang Mountains under salt stress have not been investigated to date. Following different time treatments under 500 mM salt concentrations, 239 differentially expressed gene (DEG)-related endogenous hormones were identified that exhibited four change trends, which in Profile 47 were upregulated in both species. The C-DEG genes of AUX, GA, JA, BR, ETH, and ABA endogenous hormones were significantly enriched in Opisthopappus taihangensis (O. taihangensis) and Opisthopappus longilobus (O. longilobus). During the responsive process, mainly AUX, GA, and JA biosynthesis and signal transduction were triggered in the two species. Subsequently, crosstalk further influenced BR, EHT, ABA, and MAPK signal transduction pathways to improve the salt resistance of the two species. Within the protein-protein interactions (PPI), seven proteins exhibited the highest interactions, which primarily involved two downregulated genes (SAUR and GA3ox) and eight upregulated genes (ACX, MFP2, JAZ, BRI1, BAK1, ETR, EIN2, and SNRK2) of the above pathways. The more upregulated expression of ZEP (in the ABA biosynthesis pathway), DELLA (in the GA signaling pathway), ABF (in the ABA signaling pathway), and ERF1 (in the ETH signaling pathway) in O. taihangensis revealed that it had a relatively higher salt resistance than O. longilobus. This revealed that the responsive patterns to salt stress between the two species had both similarities and differences. The results of this investigation shed light on the potential adaptive mechanisms of O. taihangensis and O. longilobus under cliff environments, while laying a foundation for the study of other cliff species in the Taihang Mountains.

The 14-3-3 Protein BdGF14a Increases the Transcriptional Regulation Activity of BdbZIP62 to Confer Drought and Salt Resistance in Tobacco

BdGF14a, a 14-3-3 gene from Brachypodium distachyon, induced by salt, H2O2, and abscisic acid (ABA), improved tolerance to drought and salt in tobacco, with a higher survival rate and longer roots under these stresses. Additionally, physiological index analyses showed that the heterologous expression of BdGF14a induced higher expression levels of antioxidant enzymes and their activities, leading to lighter DAB and NBT staining, denoting decreased H2O2 content. Additionally, the lower MDA content and ion leakage indicated enhanced cell membrane stability. Moreover, exogenous ABA resulted in shorter roots and a lower stomatal aperture in BdGF14a transgenic plants. BdGF14a interacted with NtABF2 and regulated the expression of stress-related genes. However, adding an ABA biosynthesis inhibitor suppressed most of these changes. Furthermore, similar salt and drought resistance phenotypes and physiological indicators were characterized in tobacco plants expressing BdbZIP62, an ABRE/ABF that interacts with BdGF14a. And Y1H and LUC assays showed that BdGF14a could enhance the transcription regulation activity of NtABF2 and BdbZIP62, targeting NtNECD1 by binding to the ABRE cis-element. Thus, BdGF14a confers resistance to drought and salinity through interaction with BdbZIP62 and enhances its transcriptional regulation activity via an ABA-mediated signaling pathway. Therefore, this work offers novel target genes for breeding salt- and drought-tolerant plants.

Genome-wide identification of GTE family proteins in sugarcane (Saccharum spontaneum) reveals that SsGTEL3a confers drought tolerance

The bromodomain is a highly conserved protein domain that specifically binds to acetylated lysine residues in histones, thereby activating transcription of target genes. Although some progress in Global Transcription Factor Group E (GTE) has been achieved in numerous animals and a few plant species, no systematic analysis of GTE gene families has been reported yet in sugarcane. In our study, 37 GTE and GTE-Like (GTEL) genes were characterized in the Saccharum spontaneum. All SsGTE/SsGTEL members were heterogeneously located on all chromosomes of the sugarcane genome and divided into five groups. Transcriptome data showed that SsGTEL3a was expressed at significantly higher levels under drought stress in drought-resistant varieties than in drought-sensitive varieties. Moreover, the overexpression of SsGTEL3a significantly improved the drought tolerance in Arabidopsis through improving the scavenging ability of reactive oxygen species. Additionally, an interaction between ScFAR1 and SsGTEL3a was identified, with ScFAR1 showing a positive response to drought stress in bacterium. In summary, this systematic analysis of GTE gene family in sugarcane and functional research of SsGTEL3a broadened deeper insight into their evolutionary dynamics and functional properties and provided new candidate genes for drought-resistant molecular breeding of sugarcane.

Knockout of SlbZIP68 reduces late blight resistance in tomato

Tomato (Solanum lycopersicum) is one of the most widely cultivated vegetable crop species in the world. Tomato late blight caused by Phytophthora infestans is a severe disease, which can cause serious losses in tomato production. In this study, tomato SlbZIP68 was identified as a transcription factor that can be induced by P. infestans, salicylic acid (SA) and jasmonic acid (JA). Knockout of SlbZIP68 via clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) technology revealed a significant decrease in tomato resistance to P. infestans. Furthermore, knockout of SlbZIP68 reduced the activity of defense enzymes and increased the accumulation of reactive oxygen species (ROS). Our findings also indicated that SlbZIP68 can activate the expression of the PR genes and enhance resistance to P. infestans. In addition, SlbZIP68 can bind to the PR3 and PR5 promoters and induce gene expression, as revealed by yeast one-hybrid (Y1H) and dual-luciferase (LUC) assays. These findings not only elucidate the mechanisms of response to P. infestans but also enable targeted breeding strategies for tomato resistance to P. infestans.

Wheat bZIPC1 interacts with FT2 and contributes to the regulation of spikelet number per spike

KEY MESSAGE

The wheat transcription factor bZIPC1 interacts with FT2 and affects spikelet and grain number per spike. We identified a natural allele with positive effects on these two economically important traits. Loss-of-function mutations and natural variation in the gene FLOWERING LOCUS T2 (FT2) in wheat have previously been shown to affect spikelet number per spike (SNS). However, while other FT-like wheat proteins interact with bZIP-containing transcription factors from the A-group, FT2 does not interact with any of them. In this study, we used a yeast-two-hybrid screen with FT2 as bait and identified a grass-specific bZIP-containing transcription factor from the C-group, designated here as bZIPC1. Within the C-group, we identified four clades including wheat proteins that show Y2H interactions with different sets of FT-like and CEN-like encoded proteins. bZIPC1 and FT2 expression partially overlap in the developing spike, including the inflorescence meristem. Combined loss-of-function mutations in bZIPC-A1 and bZIPC-B1 (bzipc1) in tetraploid wheat resulted in a drastic reduction in SNS with a limited effect on heading date. Analysis of natural variation in the bZIPC-B1 (TraesCS5B02G444100) region revealed three major haplotypes (H1-H3), with the H1 haplotype showing significantly higher SNS, grain number per spike and grain weight per spike than both the H2 and H3 haplotypes. The favorable effect of the H1 haplotype was also supported by its increased frequency from the ancestral cultivated tetraploids to the modern tetraploid and hexaploid wheat varieties. We developed markers for the two non-synonymous SNPs that differentiate the bZIPC-B1b allele in the H1 haplotype from the ancestral bZIPC-B1a allele present in all other haplotypes. These diagnostic markers are useful tools to accelerate the deployment of the favorable bZIPC-B1b allele in pasta and bread wheat breeding programs.

Candidate regulators of drought stress in tomato revealed by comparative transcriptomic and proteomic analyses

Drought is among the most common abiotic constraints of crop growth, development, and productivity. Integrating different omics approaches offers a possibility for deciphering the metabolic pathways and fundamental mechanisms involved in abiotic stress tolerance. Here, we explored the transcriptional and post-transcriptional changes in drought-stressed tomato plants using transcriptomic and proteomic profiles to determine the molecular dynamics of tomato drought stress responses. We identified 22467 genes and 5507 proteins, among which the expression of 3765 genes and 294 proteins was significantly changed under drought stress. Furthermore, the differentially expressed genes (DEGs) and differentially abundant proteins (DAPs) showed a good correlation (0.743). The results indicated that integrating different omics approaches is promising in exploring the multilayered regulatory mechanisms of plant drought resistance. Gene ontology (GO) and pathway analysis identified several GO terms and pathways related to stress resistance, including response to stress, abiotic stimulus, and oxidative stress. The plant hormone abscisic acid (ABA) plays pivotal roles in response to drought stress, ABA-response element binding factor (AREB) is a key positive regulator of ABA signaling. Moreover, our analysis indicated that drought stress increased the abscisic acid (ABA) content, which activated AREB1 expression to regulate the expression of TAS14, GSH-Px-1, and Hsp, ultimately improving tomato drought resistance. In addition, the yeast one-hybrid assay demonstrated that the AREB1 could bind the Hsp promoter to activate Hsp expression. Thus, this study involved a full-scale analysis of gene and protein expression in drought-stressed tomato, deepening the understanding of the regulatory mechanisms of the essential drought-tolerance genes in tomato.

A novel Pinellia ternata catalase gene PtCAT2 regulates drought tolerance in Arabidopsis by modulating ROS balance

Drought is one of the major abiotic stresses limiting agricultural production, particularly for shallow-rooted plants like Pinellia ternata. It damages plants via oxidative burst, but this effect could be mitigated by catalase (CAT). However, no studies have been reported on CAT homologs in P. ternata, a drought-sensitive plant species. In the present study, a novel CAT gene, PtCAT2, was functionally characterized via overexpression in Arabidopsis and analysis of cis-elements in its promoter. The isolated CAT gene was 1479 bp and encoded a protein containing 242 amino acids. The protein contains the CAT activity motif and the heme-binding site of a typical CAT, and the subcellular analysis indicated that the protein localizes at the cytoplasm and membrane. Moreover, the quantitative real-time reverse transcription PCR indicated that PtCAT2 is expressed ubiquitously in P. ternata and is strongly induced by drought stress and abscisic acid (ABA) signals. PtCAT2 overexpression enhanced the drought tolerance of Arabidopsis, as shown by the 30% increase in plant survival and a five-fold- increase in CAT activity. Moreover, PtCAT2-transgenic plants increased superoxide dismutase and peroxidase activities and reduced malondialdehyde, membrane leakage, and hydrogen peroxide (H2O2) (P<0.05). Furthermore, PtCAT2-transgenic plants showed higher tolerance to oxidative stress caused by exogenous H2O2 and retained higher chlorophyll and water contents than the WT. The mitochondria function was better maintained as presented by the higher oxygen consumption rate in transgenics under drought stress (P<0.05). The endogenous CATs and drought response-related genes were also upregulated in transgenic lines under drought stress, indicating that PtCAT2 confers drought stress tolerance by enhancing the H2O2 scavenging ability of plants to maintain their membrane integrity. These results improve our understanding of the drought response mechanisms and provide a potential breeding strategy for P. ternata genetic improvement.

Drought priming modulates ABF, GRFs, related microRNAs and induce metabolic adjustment during heat stress in chickpea

Drought and high temperature stress may occur concomitantly or individually in succession causing cellular dysfunctions. Abscisic acid (ABA) is a key stress regulator, and its responsive genes are controlled by ABRE (Abscisic acid Responsive Element)-binding factors (ABFs)and G-Box Regulatory factors (GRFs). Here, we identify ABFs, GRFs and targeting miRNAs in desi and kabuli chickpea. To validate their role after drought priming and subsequent high temperature stress, two contrasting chickpea varieties (PBG1 and PBG5) were primed and exposed to 32 °C, 35 °C and 38 °C for 12, 6 and 2 h respectively and analyzed for Physio-biochemical, expression of ABFs, GRFs and MiRNAs, and GC-MS based metabolite analysis. To ascertain the ABF-GRF protein-protein interactions, docking studies were carried out between the ABF3 and GRF14. Genome-wide analysis identified total 9 & 11 ABFs, and 11 GRFsin desi and kabuli respectively. Their gene structure, and motif composition were conserved in all subfamilies and only 10 and 12 genes have undergone duplication in both desi and kabuli chickpea respectively. These genes were differentially expressed in-silico. MiR172 and miR396 were identified to target ABFs and GRFs respectively. Protein-protein interaction (ABF3 and GRF14) might be successful only when the ABF3 was phosphorylated. Drought priming downregulated miR172 and miR396 and eventually upregulated targeting ABFs, and GRFs. Metabolite profiling (GC-MS) revealed the accumulation of 87 metabolites in Primed (P) and Non-Primed (NP) Chickpea plants. Tolerant cultivar (PBG5) responded better in all respects however both severity of stress and exposure are important factors and can produce broadly similar cellular response.

MicroRNA2871b of Dongxiang Wild Rice (Oryza rufipogon Griff.) Negatively Regulates Cold and Salt Stress Tolerance in Transgenic Rice Plants

Cold and salt stresses are major environmental factors that constrain rice production. Understanding their mechanisms is important to enhance cold and salt stress tolerance in rice. MicroRNAs (miRNAs) are a class of non-coding RNAs with only 21-24 nucleotides that are gene regulators in plants and animals. Previously, miR2871b expression was suppressed by cold stress in Dongxiang wild rice (DXWR, Oryza rufipogon Griff.). However, its biological functions in abiotic stress responses remain elusive. In the present study, miR2871b of DWXR was overexpressed to investigate its function under stress conditions. When miR2871b of DWXR was introduced into rice plants, the transgenic lines were more sensitive to cold and salt stresses, and their tolerance to cold and salt stress decreased. The increased expression of miR2871b in rice plants also increased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA); however, it markedly decreased the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) and the contents of proline (Pro) and soluble sugar (SS). These data suggested that miR2871b of DXWR has negative regulatory effects on cold and salt stress tolerance. Meanwhile, 412 differentially expressed genes (DEGs) were found in rice transgenic plants using transcriptome sequencing, among which 266 genes were up-regulated and 146 genes were down-regulated. Furthermore, the upstream cis-acting elements and downstream targets of miR2871b were predicted and analyzed, and several critical acting elements (ABRE and TC-rich repeats) and potential target genes (LOC_Os03g41200, LOC_Os07g47620, and LOC_Os04g30260) were obtained. Collectively, these results generated herein further elucidate the vital roles of miR2871b in regulating cold and salt responses of DXWR.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

CONSTANS interacts with and antagonizes ABF transcription factors during salt stress under long-day conditions

CONSTANS (CO) is a critical regulator of flowering that combines photoperiodic and circadian signals in Arabidopsis (Arabidopsis thaliana). CO is expressed in multiple tissues, including seedling roots and young leaves. However, the roles and underlying mechanisms of CO in modulating physiological processes outside of flowering remain obscure. Here, we show that the expression of CO responds to salinity treatment. CO negatively mediated salinity tolerance under long-day (LD) conditions. Seedlings from co-mutants were more tolerant to salinity stress, whereas overexpression of CO resulted in plants with reduced tolerance to salinity stress. Further genetic analyses revealed the negative involvement of GIGANTEA (GI) in salinity tolerance requires a functional CO. Mechanistic analysis demonstrated that CO physically interacts with 4 critical basic leucine zipper (bZIP) transcription factors; ABSCISIC ACID-RESPONSIVE ELEMENT BINDING FACTOR1 (ABF1), ABF2, ABF3, and ABF4. Disrupting these ABFs made plants hypersensitive to salinity stress, demonstrating that ABFs enhance salinity tolerance. Moreover, ABF mutations largely rescued the salinity-tolerant phenotype of co-mutants. CO suppresses the expression of several salinity-responsive genes and influences the transcriptional regulation function of ABF3. Collectively, our results show that the LD-induced CO works antagonistically with ABFs to modulate salinity responses, thus revealing how CO negatively regulates plant adaptation to salinity stress.

Genome-wide analysis of the U-box E3 ubiquitin ligase family role in drought tolerance in sesame (Sesamum indicum L.)

Plant U-box (PUB) proteins belong to a class of ubiquitin ligases essential in various biological processes. Sesame (Sesamum indicum L.) is an important and worldwide cultivated oilseed crop. However few studies have been conducted to explore the role of PUBs in drought tolerance in sesame. This study identified a total of 56 members of the sesame PUB family (SiPUB) genes distributed unevenly across all 13 chromosomes. Based on phylogenetic analysis, all 56 SiPUB genes were classified into six groups with various structures and motifs. Cis-acting element analysis suggested that the SiPUB genes are involved in response to various stresses including drought. Based on RNA-seq analysis and quantitative real-time PCR, we identified nine SiPUB genes with significantly different expression profiles under drought stress. The expression patterns of six SiPUB genes in root, leaf and stem tissues corroborated the reliability of the RNA-seq datasets. These findings underscore the importance of SiPUB genes in enhancing drought tolerance in sesame plants. Our study provides novel insights into the evolutionary patterns and variations of PUB genes in sesame and lays the foundation for comprehending the functional characteristics of SiPUB genes under drought-induced stress conditions.

Systematic Identification and Functional Analysis of the Hypericum perforatum L. bZIP Gene Family Indicating That Overexpressed HpbZIP69 Enhances Drought Resistance

Basic leucine zipper (bZIP) transcription factors play significant roles in plants' growth and development processes, as well as in response to biological and abiotic stresses. Hypericum perforatum is one of the world's top three best-selling herbal medicines, mainly used to treat depression. However, there has been no systematic identification or functional analysis of the bZIP gene family in H. perforatum. In this study, 79 HpbZIP genes were identified. Based on phylogenetic analysis, the HpbZIP gene family was divided into ten groups, designated A-I and S. The physicochemical properties, gene structures, protein conserved motifs, and Gene Ontology enrichments of all HpbZIPs were systematically analyzed. The expression patterns of all genes in different tissues of H. perforatum (i.e., root, stem, leaf, and flower) were analyzed by qRT-PCR, revealing the different expression patterns of HpbZIP under abiotic stresses. The HpbZIP69 protein is localized in the nucleus. According to the results of the yeast one-hybrid (Y1H) assays, HpbZIP69 can bind to the HpASMT2 (N-acetylserotonin O-methyltransferase) gene promoter (G-box cis-element) to activate its activity. Overexpressing HpbZIP69 in Arabidopsis wild-type lines enhanced their tolerance to drought. The MDA and H2O2 contents were significantly decreased, and the activity of superoxide dismutase (SOD) was considerably increased under the drought stress. These results may aid in additional functional studies of HpbZIP transcription factors, and in cultivating drought-resistant medicinal plants.

A pervasive phosphorylation cascade modulation of plant transcription factors in response to abiotic stress

MAIN CONCLUSION

Transcriptional regulation of stress-responsive genes is a crucial step in establishing the mechanisms behind plant abiotic stress tolerance. A sensitive method of regulating transcription factors activity, stability, protein interaction, and subcellular localization is through phosphorylation. This review highlights a widespread regulation mechanism that involves phosphorylation of plant TFs in response to abiotic stress. Abiotic stress is one of the main components limiting crop yield and sustainability on a global scale. It greatly reduces the land area that is planted and lowers crop production globally. In all living organisms, transcription factors (TFs) play a crucial role in regulating gene expression. They participate in cell signaling, cell cycle, development, and plant stress response. Plant resilience to diverse abiotic stressors is largely influenced by TFs. Transcription factors modulate gene expression by binding to their target gene's cis-elements, which are impacted by genomic characteristics, DNA structure, and TF interconnections. In this review, we focus on the six major TFs implicated in abiotic stress tolerance, namely, DREB, bZIP, WRKY, ABF, MYB, and NAC, and the cruciality of phosphorylation of these transcription factors in abiotic stress signaling, as protein phosphorylation has emerged as one of the key post-translational modifications, playing a critical role in cell signaling, DNA amplification, gene expression and differentiation, and modification of other biological configurations. These TFs have been discovered after extensive study as stress-responsive transcription factors which may be major targets for crop development and important contributors to stress tolerance and crop production.

The GhMAP3K62-GhMKK16-GhMPK32 kinase cascade regulates drought tolerance by activating GhEDT1-mediated ABA accumulation in cotton

INTRODUCTION

Drought is the principal abiotic stress that severely impacts cotton (Gossypium hirsutum) growth and productivity. Upon sensing drought, plants activate stress-related signal transduction pathways, including ABA signal and mitogen-activated protein kinase (MAPK) cascade. However, as the key components with the fewest members in the MAPK cascade, the function and regulation of GhMKKs need to be elucidated. In addition, the relationship between MAPK module and the ABA core signaling pathway remains incompletely understood.

OBJECTIVE

Here we aim to elucidate the molecular mechanism of cotton response to drought, with a focus on mitogen-activated protein kinase (MAPK) cascades activating ABA signaling.

METHODS

Biochemical, molecular and genetic analysis were used to study the GhMAP3K62-GhMKK16-GhMPK32-GhEDT1 pathway genes.

RESULTS

A nucleus- and membrane-localized MAPK cascade pathway GhMAP3K62-GhMKK16-GhMPK32, which targets and phosphorylates the nuclear-localized transcription factor GhEDT1, to activate downstream GhNCED3 to mediate ABA-induced stomatal closure and drought response was characterized in cotton. Overexpression of GhMKK16 promotes ABA accumulation, and enhances drought tolerance via regulating stomatal closure under drought stress. Conversely, RNAi-mediated knockdown of GhMKK16 expression inhibits ABA accumulation, and reduces drought tolerance. Virus-induced gene silencing (VIGS)-mediated knockdown of either GhMAP3K62, GhMPK32 or GhEDT1 expression represses ABA accumulation and reduces drought tolerance through inhibiting stomatal closure. Expression knockdown of GhMPK32 or GhEDT1 in GhMKK16-overexpressing cotton reinstates ABA content and stomatal opening-dependent drought sensitivity to wild type levels. GhEDT1 could bind to the HD boxes in the promoter of GhNCED3 to activate its expression, resulting in ABA accumulation. We propose that the MAPK cascade GhMAP3K62-GhMKK16-GhMPK32 pathway functions on drought response through ABA-dependent stomatal movement in cotton.

Allelic variation in transcription factor PtoWRKY68 contributes to drought tolerance in Populus

Drought stress limits woody species productivity and influences tree distribution. However, dissecting the molecular mechanisms that underpin drought responses in forest trees can be challenging due to trait complexity. Here, using a panel of 300 Chinese white poplar (Populus tomentosa) accessions collected from different geographical climatic regions in China, we performed a genome-wide association study (GWAS) on seven drought-related traits and identified PtoWRKY68 as a candidate gene involved in the response to drought stress. A 12-bp insertion and/or deletion and three nonsynonymous variants in the PtoWRKY68 coding sequence categorized natural populations of P. tomentosa into two haplotype groups, PtoWRKY68hap1 and PtoWRKY68hap2. The allelic variation in these two PtoWRKY68 haplotypes conferred differential transcriptional regulatory activities and binding to the promoters of downstream abscisic acid (ABA) efflux and signaling genes. Overexpression of PtoWRKY68hap1 and PtoWRKY68hap2 in Arabidopsis (Arabidopsis thaliana) ameliorated the drought tolerance of two transgenic lines and increased ABA content by 42.7% and 14.3% compared to wild-type plants, respectively. Notably, PtoWRKY68hap1 (associated with drought tolerance) is ubiquitous in accessions in water-deficient environments, whereas the drought-sensitive allele PtoWRKY68hap2 is widely distributed in well-watered regions, consistent with the trends in local precipitation, suggesting that these alleles correspond to geographical adaptation in Populus. Moreover, quantitative trait loci analysis and an electrophoretic mobility shift assay showed that SHORT VEGETATIVE PHASE (PtoSVP.3) positively regulates the expression of PtoWRKY68 under drought stress. We propose a drought tolerance regulatory module in which PtoWRKY68 modulates ABA signaling and accumulation, providing insight into the genetic basis of drought tolerance in trees. Our findings will facilitate molecular breeding to improve the drought tolerance of forest trees.

Introducing sorghum DREB2 gene in maize (Zea mays L.) to improve drought and salinity tolerance

Salinity and drought are significant abiotic stresses causing a considerable loss of seed and biomass yield in most commercial crops. Some of the most critical players in the abscisic acid pathway are drought responsive element binding (DREB) proteins that are a part of AP2/ethylene response factor transcription factors that bind to promoters of some family genes needed to be expressed under abiotic stresses. In this study, salt- and drought-tolerant maize plants were produced from immature maize embryos bombarded by the sorghum (Sorghum bicolor L.) DREB2 gene that is linked to hygromycin resistance (hpt) genes. The putative transgenic calli were transferred to an N6 medium containing 1 mg/L benzylaminopurine and 50 mg/L hygromycin. Regeneration was completed after 4 weeks on selective media under a 16/8 h light/dark condition at 25°C. Polymerase chain reaction (PCR) and reverse transcription-PCR approved the existence of upstream promoter (rd29a), hpt gene, and the expression of the DREB2 in transgenes up to the third generation (T2). It was found that the K+/Na+ ratio and the amount of proline as a screening indicator were higher in transgenic plants compared to their wild types. This result is a promising model to enhance maize tolerance to abiotic stressors.

Genetic diversity Analysis using molecular markers of some rice varieties for Physiological, biochemical and yield Traits under water deficit condition.. [DOI: 10.21203/rs.3.rs-3111398/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Rice is a major staple food crop all over the world. Recent climate change trends forecast an increase in drought severity, necessitating the creation of novel drought-tolerant rice cultivars in order to continue rice production in this ecosystem. This study was carried out at the experimental farm of the rice research and training center (RRTC) using the randomized complete block design (RCBD) to assess the impact of water scarcity on eight rice varieties by identifying differences in physiological and biochemical responses among drought-sensitive and resistant rice varieties, in addition applying two PCR-based molecular marker systems ISSR and SCoT to assess the genetic diversity among the studied rice varieties. The results revealed that, Water shortage stress significantly reduced relative water content, total chlorophyll content, grain yield, and yield characteristics. while, it significantly raised proline content and antioxidant enzyme activity (CAT, APX, and SOD). The combined analysis of variance demonstrated that the mean squares for environments, varieties, and their interaction were highly significant for all investigated traits, suggesting that the germplasm used in the study had significant genetic diversity from one environment (normal irrigation) to another (water deficit) and could rank differently in both of them. Mean performance data showed that, Puebla and Hispagran varieties were selected as the most favourable varieties for most physiological and biochemical parameters studied, as well as yield traits which recorded the highest desirable values under both irrigation treatments. They were recommended for use in rice hybrid breeding programmes for water scarcity tolerance. Genetic Similarity and Cluster Analysis revealed that, the both molecular markers exhibited comparable genetic diversity values but a higher level of polymorphism was represented by ISSR. This indicates the high efficiency of both markers in discriminating the tested varieties. The dendrogram generated by ISSR and SCoT markers combined data divided the varieties into two major clusters. Cluster I consisted of the genotype Sakha 106. Cluster II retained seven varieties, which were further divided into two sub-clusters; Sakha 101, Sakha 105, Sakha 106, Sakha 107 constituted the first subgroup, while Giza 177, Hispagran, and Puebla formed the second one.

The ABA-induced NAC transcription factor MdNAC1 interacts with a bZIP-type transcription factor to promote anthocyanin synthesis in red-fleshed apples

Anthocyanins are valuable compounds in red-fleshed apples. The MdMYB10 transcription factor is an important regulator of the anthocyanin synthesis pathway. However, other transcription factors are key components of the complex network controlling anthocyanin synthesis and should be more thoroughly characterized. In this study, we used a yeast-based screening technology to identify MdNAC1 as a transcription factor that positively regulates anthocyanin synthesis. The overexpression of MdNAC1 in apple fruits and calli significantly promoted the accumulation of anthocyanins. In binding experiments, we demonstrated that MdNAC1 combines with the bZIP-type transcription factor MdbZIP23 to activate the transcription of MdMYB10 and MdUFGT. Our analyses also indicated that the expression of MdNAC1 is strongly induced by ABA because of the presence of an ABRE cis-acting element in its promoter. Additionally, the accumulation of anthocyanins in apple calli co-transformed with MdNAC1 and MdbZIP23 increased in the presence of ABA. Therefore, we revealed a novel anthocyanin synthesis mechanism involving the ABA-induced transcription factor MdNAC1 in red-fleshed apples.

Comparative Metabolomics Profiling Reveals Key Metabolites and Associated Pathways Regulating Tuber Dormancy in White Yam (Dioscorea rotundata Poir.)

Yams are economic and medicinal crops with a long growth cycle, spanning between 9-11 months due to their prolonged tuber dormancy. Tuber dormancy has constituted a major constraint in yam production and genetic improvement. In this study, we performed non-targeted comparative metabolomic profiling of tubers of two white yam genotypes, (Obiaoturugo and TDr1100873), to identify metabolites and associated pathways that regulate yam tuber dormancy using gas chromatography-mass spectrometry (GC-MS). Yam tubers were sampled between 42 days after physiological maturity (DAPM) till tuber sprouting. The sampling points include 42-DAPM, 56-DAPM, 87DAPM, 101-DAPM, 115-DAPM, and 143-DAPM. A total of 949 metabolites were annotated, 559 in TDr1100873 and 390 in Obiaoturugo. A total of 39 differentially accumulated metabolites (DAMs) were identified across the studied tuber dormancy stages in the two genotypes. A total of 27 DAMs were conserved between the two genotypes, whereas 5 DAMs were unique in the tubers of TDr1100873 and 7 DAMs were in the tubers of Obiaoturugo. The differentially accumulated metabolites (DAMs) spread across 14 major functional chemical groups. Amines and biogenic polyamines, amino acids and derivatives, alcohols, flavonoids, alkaloids, phenols, esters, coumarins, and phytohormone positively regulated yam tuber dormancy induction and maintenance, whereas fatty acids, lipids, nucleotides, carboxylic acids, sugars, terpenoids, benzoquinones, and benzene derivatives positively regulated dormancy breaking and sprouting in tubers of both yam genotypes. Metabolite set enrichment analysis (MSEA) revealed that 12 metabolisms were significantly enriched during yam tuber dormancy stages. Metabolic pathway topology analysis further revealed that six metabolic pathways (linoleic acid metabolic pathway, phenylalanine metabolic pathway, galactose metabolic pathway, starch and sucrose metabolic pathway, alanine-aspartate-glutamine metabolic pathways, and purine metabolic pathway) exerted significant impact on yam tuber dormancy regulation. This result provides vital insights into molecular mechanisms regulating yam tuber dormancy.

Role of bZIP Transcription Factors in Plant Salt Stress

Soil salinity has become an increasingly serious problem worldwide, greatly limiting crop development and yield, and posing a major challenge to plant breeding. Basic leucine zipper (bZIP) transcription factors are the most widely distributed and conserved transcription factors and are the main regulators controlling various plant response processes against external stimuli. The bZIP protein contains two domains: a highly conserved, DNA-binding alkaline region, and a diverse leucine zipper, which is one of the largest transcription factor families in plants. Plant bZIP is involved in many biological processes, such as flower development, seed maturation, dormancy, and senescence, and plays an important role in abiotic stresses such as salt damage, drought, cold damage, osmotic stress, mechanical damage, and ABA signal response. In addition, bZIP is involved in the regulation of plant response to biological stresses such as insect pests and pathogen infection through salicylic acid, jasmonic acid, and ABA signal transduction pathways. This review summarizes and discusses the structural characteristics and functional characterization of the bZIP transcription factor group, the bZIP transcription factor complex and its molecular regulation mechanisms related to salt stress resistance, and the regulation of transcription factors in plant salt stress resistance. This review provides a theoretical basis and research ideas for further exploration of the salt stress-related functions of bZIP transcription factors. It also provides a theoretical basis for crop genetic improvement and green production in agriculture.

Highlight Induced Transcriptional Priming against a Subsequent Drought Stress in Arabidopsis thaliana

In plants, priming allows a more rapid and robust response to recurring stresses. However, while the nature of plant response to a single stress can affect the subsequent response to the same stress has been deeply studied, considerably less is known on how the priming effect due to one stress can help plants cope with subsequent different stresses, a situation that can be found in natural ecosystems. Here, we investigate the potential priming effects in Arabidopsis plants subjected to a high light (HL) stress followed by a drought (D) stress. The cross-stress tolerance was assessed at the physiological and molecular levels. Our data demonstrated that HL mediated transcriptional priming on the expression of specific stress response genes. Furthermore, this priming effect involves both ABA-dependent and ABA-independent responses, as also supported by reduced expression of these genes in the aba1-3 mutant compared to the wild type. We have also assessed several physiological parameters with the aim of seeing if gene expression coincides with any physiological changes. Overall, the results from the physiological measurements suggested that these physiological processes did not experience metabolic changes in response to the stresses. In addition, we show that the H3K4me3 epigenetic mark could be a good candidate as an epigenetic mark in priming response. Overall, our results help to elucidate how HL-mediated priming can limit D-stress and enhance plant responses to stress.

The bZIP transcription factor SlAREB1 regulates anthocyanin biosynthesis in response to low temperature in tomato

Low temperature and abscisic acid (ABA) are the two main factors that induce anthocyanin synthesis; however, their potential relationships in governing anthocyanin biosynthesis in Solanum lycopersicum (tomato) seedlings remains unclear. Our study revealed the involvement of the transcription factor SlAREB1 in the low-temperature response of tomato seedlings via the ABA-dependent pathway, for a specific temperature range. The overexpression of SlAREB1 enhanced the expression of anthocyanin-related genes and the accumulation of anthocyanins, especially under low-temperature conditions, whereas silencing SlAREB1 dramatically reduced gene expression and anthocyanin accumulation. There is a direct interaction between SlAREB1 and the promoters of SlDFR and SlF3'5'H, which are structural genes that impact anthocyanin biosynthesis. SlAREB1 can regulate anthocyanins through controlling SlDFR and SlF3'5'H expression. Accordingly, SlAREB1 takes charge of regulating anthocyanin biosynthesis in tomato seedlings via the ABA-dependent pathway at low temperatures.

Shoot differentiation from Dendrocalamus brandisii callus and the related physiological roles of sugar and hormones during shoot differentiation

Only a few calli regeneration systems of bamboos were successfully established, which limited the research on physiological mechanism of callus differentiation. In this study, we successfully established the callus differentiation systems of Dendrocalamus brandisii via seeds. The results showed that the best medium for callus induction of D. brandisii seeds was basal MS media amended with 5.0 mg L-1 2,4-D and 0.5 mg L-1 KT, and the optimal medium for shoot differentiation was the basal MS media supplemented with 4.0 mg L-1 BA and 0.5 mg L-1 NAA. Callus tissues had apparent polarity in cell arrangement, and developed their own meristematic cell layers. α-amylase, STP and SUSY played a dominant role in carbohydrates degradation in callus during shoot differentiation. PPP and TCA pathways up-regulated in the shoot-differentiated calli. The dynamics of BA and KT contents in calli was consistent with their concentrations applied in medium. IAA synthesis and the related signal transduction were down-regulated, while the endogenous CTKs contents were up-regulated by the exogenous CTKs application in shoot-differentiated calli, and their related synthesis, transport and signal transduction pathways were also up-regulated. The downregulated signal transduction pathways of IAA and ABA revealed that they did not play the key role in shoot differentiation of bamboos. GAs also played a role in shoot differentiation based on the down-regulation of DELLA and the up-regulation of PIF4 genes. The overexpression of DbSNRK2 and DbFIF4 genes further confirmed the negative role of ABA and the positive role of GAs in shoot differentiation.

Proteomics analysis of a tobacco variety resistant to brown spot disease and functional characterization of NbMLP423 in Nicotiana benthamiana

BACKGROUND

Tobacco brown spot disease is an important disease caused by Alternaria alternata that affects tobacco production and quality worldwide. Planting resistant varieties is the most economical and effective way to control this disease. However, the lack of understanding of the mechanism of tobacco resistance to tobacco brown spot has hindered progress in the breeding of resistant varieties.

METHODS AND RESULTS

In this study, differentially expressed proteins (DEPs), including 12 up-regulated and 11 down-regulated proteins, were screened using isobaric tags for relative and absolute quantification (iTRAQ) by comparing resistant and susceptible pools and analyzing the associated functions and metabolic pathways. Significantly up-regulated expression of the major latex-like protein gene 423 (MLP 423) was detected in both the resistant parent and the population pool. Bioinformatics analysis showed that the NbMLP423 cloned in Nicotiana benthamiana had a similar structure to the NtMLP423 in Nicotiana tabacum, and that expression of both genes respond rapidly to Alternaria alternata infection. NbMLP423 was then used to study the subcellular localization and expression in different tissues, followed by both silencing and the construction of an overexpression system for NbMLP423. The silenced plants demonstrated inhibited TBS resistance, while the overexpressed plants exhibited significantly enhanced resistance. Exogenous applications of plant hormones, such as salicylic acid, had a significant inducing effect on NbMLP423 expression.

CONCLUSIONS

Taken together, our results provide insights into the role of NbMLP423 in plants against tobacco brown spot infection and provide a foundation for obtaining resistant tobacco varieties through the construction of new candidate genes of the MLP subfamily.

The transcription factor PbrbZIP52 positively affects pear pollen tube longevity by promoting callose synthesis

In pear (Pyrus bretschneideri), pollen tube growth is critical for the double fertilization associated with seed setting, which in turn affects fruit yield. The normal deposition of callose mediates the polar growth of pollen tubes. However, the mechanism regulating callose synthesis in pollen tubes remains relatively uncharacterized. In this study, we revealed that the typical pear pollen tube lifecycle has a semi-growth duration (GD50) of 16.16 h under in vitro culture conditions. Moreover, callose plugs were deposited throughout the pollen tube lifecycle. The formation of callose plugs was inhibited by 2-deoxy-D-glucose, which also accelerated the senescence of pear pollen tubes. Additionally, PbrCalS1B.1, which encodes a plasma membrane-localized callose synthase, was expressed specifically in pollen tubes and restored the fertility of the Arabidopsis (Arabidopsis thaliana) cals5 mutant, in which callose synthesis is inhibited. However, this restoration of fertility was impaired by the transient silencing of PbrCalS1B.1, which restricts callose plug formation and shortens the pear pollen tube lifecycle. More specifically, PbrbZIP52 regulated PbrCalS1B.1 transcription by binding to promoter A-box elements to maintain the periodic formation of callose plugs and normal pollen tube growth, ultimately leading to double fertilization. This study confirmed that PbrbZIP52 positively affects pear pollen tube longevity by promoting callose synthesis. This finding may be useful for breeding high-yielding pear cultivars and stabilizing fruit setting in commercial orchards.

Dual-function C2H2-type zinc-finger transcription factor GmZFP7 contributes to isoflavone accumulation in soybean

Isoflavones are a class of secondary metabolites produced by legumes and play important roles in human health and plant stress tolerance. The C2H2 zinc-finger transcription factor (TF) functions in plant stress tolerance, but little is known about its function in isoflavone regulation in soybean (Glycine max). Here, we report a C2H2 zinc-finger TF gene, GmZFP7, which regulates isoflavone accumulation in soybean. Overexpressing GmZFP7 increased the isoflavone concentration in both transgenic hairy roots and plants. By contrast, silencing GmZFP7 expression significantly reduced isoflavone levels. Metabolomic and qRT-PCR analysis revealed that GmZFP7 can increase the flux of the phenylpropanoid pathway. Furthermore, dual-luciferase and electrophoretic mobility shift assays showed that GmZFP7 regulates isoflavone accumulation by influencing the expression of Isoflavone synthase 2 (GmIFS2) and Flavanone 3 β-hydroxylase 1 (GmF3H1). In this study, we demonstrate that GmZFP7 contributes to isoflavone accumulation by regulating the expression of the gateway enzymes (GmIFS2 and GmF3H1) of competing phenylpropanoid pathway branches to direct the metabolic flux into isoflavone. A haplotype analysis indicated that important natural variations were present in GmZFP7 promoters, with P-Hap1 and P-Hap3 being the elite haplotypes. Our findings provide insight into how GmZFP7 regulates the phenylpropanoid pathway and enhances soybean isoflavone content.

Genome assembly and genetic dissection of a prominent drought-resistant maize germplasm

In the context of climate change, drought is one of the most limiting factors that influence crop production. Maize, as a major crop, is highly vulnerable to water deficit, which causes significant yield loss. Thus, identification and utilization of drought-resistant germplasm are crucial for the genetic improvement of the trait. Here we report on a high-quality genome assembly of a prominent drought-resistant genotype, CIMBL55. Genomic and genetic variation analyses revealed that 65 favorable alleles of 108 previously identified drought-resistant candidate genes were found in CIMBL55, which may constitute the genetic basis for its excellent drought resistance. Notably, ZmRtn16, encoding a reticulon-like protein, was found to contribute to drought resistance by facilitating the vacuole H+-ATPase activity, which highlights the role of vacuole proton pumps in maize drought resistance. The assembled CIMBL55 genome provided a basis for genetic dissection and improvement of plant drought resistance, in support of global food security.

Identification of Small RNAs Associated with Salt Stress in Chrysanthemums through High-Throughput Sequencing and Bioinformatics Analysis

The Chrysanthemum variety “Niu 9717” exhibits excellent characteristics as an ornamental plant and has good salt resistance. In this study, this plant was treated with 200 mM NaCl for 12 h followed by high-throughput sequencing of miRNA and degradome. Subsequently, the regulatory patterns of potential miRNAs and their target genes were searched to elucidate how Chrysanthemum miRNAs respond to salt. From the root and leaf samples, we identified a total of 201 known miRNAs belonging to 40 families; furthermore, we identified 79 new miRNAs, of which 18 were significantly differentially expressed (p < 0.05). The expressed miRNAs, which targeted a total of 144 mRNAs in the leaf and 215 mRNAs in the root, formed 144 and 226 miRNA–target pairs in roots and leaves, respectively. Combined with the miRNA expression profile, degradome and transcriptome data were then analyzed to understand the possible effects of the miRNA target genes and their pathways on salt stress. The identified genes were mostly located in pathways related to hormone signaling during plant growth and development. Overall, these findings suggest that conserved and novel miRNAs may improve salt tolerance through the regulation of hormone signal synthesis or expression of genes involved in hormone synthesis.

Endosperm cellularization failure induces a dehydration-stress response leading to embryo arrest

The endosperm is a nutritive tissue supporting embryo growth in flowering plants. Most commonly, the endosperm initially develops as a coenocyte (multinucleate cell) and then cellularizes. This process of cellularization is frequently disrupted in hybrid seeds generated by crosses between different flowering plant species or plants that differ in ploidy, resulting in embryo arrest and seed lethality. The reason for embryo arrest upon cellularization failure remains unclear. In this study, we show that triploid Arabidopsis thaliana embryos surrounded by uncellularized endosperm mount an osmotic stress response that is connected to increased levels of abscisic acid (ABA) and enhanced ABA responses. Impairing ABA biosynthesis and signaling aggravated triploid seed abortion, while increasing endogenous ABA levels as well as the exogenous application of ABA-induced endosperm cellularization and suppressed embryo growth arrest. Taking these results together, we propose that endosperm cellularization is required to establish dehydration tolerance in the developing embryo, ensuring its survival during seed maturation.

Transgenerational effects of chromium stress at the phenotypic and molecular level in Arabidopsis thaliana

In this study, we describe the results obtained in a study of the transgenerational phenotypic effects of chromium (Cr) stress on the model plant species Arabidopsis thaliana. The F1 generation derived from parents grown under chronic and medium chronic stress showed significantly higher levels of the maximal effective concentration (EC₅₀) compared with F1 plants generated from unstressed parents. Moreover, F1 plants from Cr-stressed parents showed a higher germination rate when grown in the presence of Cr. F1 plants derived from parents cultivated under chronic Cr stress displayed reduced hydrogen peroxide levels under Cr stress compared to controls. At lower Cr stress levels, F1 plants were observed to activate promptly more genes involved in Cr stress responses than F0 plants, implying a memory effect linked to transgenerational priming. At higher Cr levels, and at later stages, F1 plants modulated significantly fewer genes than F0 plants, implying a memory effect leading to Cr stress adaptation. Several bHLH transcription factors were induced by Cr stress in F1 but not in F0 plants, including bHLH100, ORG2 and ORG3. F1 plants optimized gene expression towards pathways linked to iron starvation response. A model of the transcriptional regulation of transgenerational memory to Cr stress is presented here, and could be applied for other heavy metal stresses.

Characterization and expression analysis of basic leucine zipper (bZIP) transcription factors responsive to chilling injury in peach fruit

BACKGROUND

Peach (Prunus persica L.) is prone to chilling injury as exhibited by inhibition of the ethylene production, failure in softening, and the manifestation of internal browning. The basic leucine zipper (bZIP) transcription factors play an essential role in regulatory networks that control many processes associated with physiological, abiotic and biotic stress responses in fruits. Formerly, the underlying molecular and regulatory mechanism of (bZIP) transcription factors responsive to chilling injury in peach fruit is still elusive.

METHODS AND RESULTS

In the current experiment, the solute peach 'Zhongyou Peach No. 13' was used as the test material and cold storage at low temperature (4 °C). It was found that long-term low-temperature storage induced the production of ethylene, the hardness of the pulp decreased, and the low temperature also induced ABA accumulation. The changes of ABA and ethylene in peach fruits during low-temperature storage were clarified. Since the bZIP transcription factor is involved in the regulation of downstream pathways of ABA signals, 47 peach bZIP transcription factor family genes were identified through bioinformatics analysis. Further based on RT-qPCR analysis, 18 PpbZIP genes were discovered to be expressed in refrigerated peach fruits. Among them, the expression of PpbZIP23 and PpbZIP25 was significantly reduced during the refrigeration process, the promoter analysis of these genes found that this region contains the MYC/MYB/ABRES binding element, but not the DRES/CBFS element, indicating that the expression may be regulated by the ABA-dependent cold induction pathway, thereby responding to chilling injury in peach fruit.

CONCLUSIONS

Over investigation will provide new insights for further postharvest protocols related to molecular changes during cold storage and will prove a better cope for chilling injury.

Identification of ABF/AREB gene family in tomato (Solanum lycopersicum L.) and functional analysis of ABF/AREB in response to ABA and abiotic stresses

Abscisic acid (ABA) is a plant hormone that plays an important regulatory role in plant growth and stress response. The AREB (ABA-responsive element binding protein)/ABF (ABRE-binding factor) are important ABA-signaling components that participate in abiotic stress response. However, genome-scale analysis of ABF/AREB has not been systemically investigated in tomato. This study was conducted to identify tomato ABF/AREB family members and analyze their response to ABA and abiotic stresses. The results show that a total of 10 ABF/AREB members were identified in tomato, which are randomly distributed on five chromosomes. Domain analysis showed that these members exhibit high protein similarity, especially in the basic leucine zipper (bZIP) domain region. Subcellular localization analysis indicated that all 10 ABF/AREB members are localized in the nucleus. Phylogenetic tree analysis showed that tomato ABF/AREB genes are divided into two groups, and they are similar with the orthologs of other plants. The analysis of cis-acting elements showed that most tomato ABF/AREB genes contain a variety of hormones and stress-related elements. Expression profiles of different tissues indicated that SlABF2 and SlABF10 play an important role in fruit ripening. Finally, qRT-PCR analysis revealed that 10 tomato ABF/AREB genes respond to ABA, with SlABF3 being the most sensitive. SlABF3, SlABF5 and SlABF10 positively respond to salt and cold stresses. SlABF1, SlABF3 and SlABF10 are significantly induced under UV radiation treatment. SlABF3 and SlABF5 are significantly induced in osmotic stress. Overall, this study may provide insight into the role of tomato ABF/AREB homologues in plant response to abiotic stresses, which laid a foundation for future functional study of ABF/AREB in tomato.

LoSWEET14, a Sugar Transporter in Lily, Is Regulated by Transcription Factor LoABF2 to Participate in the ABA Signaling Pathway and Enhance Tolerance to Multiple Abiotic Stresses in Tobacco

Sugar transport and distribution plays an important role in lily bulb development and resistance to abiotic stresses. In this study, a member of the Sugar Will Eventually be Exported Transporters (SWEET) gene family, LoSWEET14, from Oriental hybrid lily 'Sorbonne' was identified. LoSWEET14 encodes a protein of 278 amino acids and is capable of transporting sucrose and some types of hexoses. The transcript level of the LoSWEET14 gene was significantly increased under various stress conditions including drought, cold, salt stresses, and abscisic acid (ABA) treatment. Overexpression of LoSWEET14 in tobacco (Nicotiana tabacum) showed that the transgenic lines had larger leaves, accumulated more soluble sugars, and were more resistant to drought, cold, and salt stresses, while becoming more sensitive to ABA compared with wild-type lines. Promoter analysis revealed that multiple stress-related cis-acting elements were found in the promoter of LoSWEET14. According to the distribution of cis-acting elements, different lengths of 5'-deletion fragments were constructed and the LoSWEET14-pro3(-540 bp) was found to be able to drive GUS gene expression in response to abiotic stresses and ABA treatment. Furthermore, a yeast one hybrid (Y1H) assay proved that the AREB/ABF (ABRE-binding protein/ABRE-binding factor) from lilies (LoABF2) could bind to the promoter of LoSWEET14. These findings indicated that LoSWEET14 is induced by LoABF2 to participate in the ABA signaling pathway to promote soluble sugar accumulation in response to multiple abiotic stresses.

Overexpression of GhABF3 increases cotton(Gossypium hirsutum L.) tolerance to salt and drought

Background

Plants suffer from various abiotic stresses during their lifetime, of which drought and salt stresses are two main factors limiting crop yield and quality. Previous studies have shown that abscisic acid (ABA) responsive element binding protein (AREB)/ ABRE binding factors (ABFs) in bZIP transcription factors are involved in plant stress response in an ABA-dependent manner. However, little is known about the properties and functions of AREB/ABFs, especially ABF3, in cotton.

Results

Here, we reported the cloning and characterization of GhABF3. Expression of GhABF3 was induced by drought,salt and ABA treatments. Silencing of GhABF3 sensitized cotton to drought and salt stress, which was manifested in decreased cellular antioxidant capacity and chlorophyll content. Overexpression of GhABF3 significantly improved the drought and salinity tolerance of Arabidopsis and cotton. Exogenous expression of GhABF3 resulted in longer root length and less leaf wilting under stress conditions in Arabidopsis thaliana. Overexpressing GhABF3 significantly improved salt tolerance of upland cotton by reducing the degree of cellular oxidation, and enhanced drought tolerance by decreasing leaf water loss rate. The increased expression of GhABF3 up-regulated the transcriptional abundance of downstream ABA-inducible genes under salt stress in Arabidopsis.

Conclusion

In conclusion, our results demonstrated that GhABF3 plays an important role in plant drought and salt tolerance. Manipulation of GhABF3 by biotechnology might be an important strategy to alter the stress resistance of cotton.

Regulation of salt tolerance in the roots of Zea mays by L-histidine through transcriptome analysis

Soil salinization is an important worldwide environmental problem and the main reason to reduce agricultural productivity. Recent findings suggested that histidine is a crucial residue that influences the ROS reduction and improves the plants' tolerance to salt stress. Herein, we conducted experiments to understand the underlying regulatory effects of histidine on maize root system under salt stress (100 mM NaCl solution system). Several antioxidant enzymes were determined. The related expressed genes (DEGs) with its pathways were observed by Transcriptome technologies. The results of the present study confirmed that histidine can ameliorate the adverse effects of salt stress on maize root growth. When the maize roots exposed to 100 mM NaCl were treated with histidine, the accumulation of superoxide anion radicals, hydrogen peroxide, and malondialdehyde, and the content of nitrate nitrogen and ammonium nitrogen were significantly reduced; while the activities of superoxide dismutase, peroxidase, catalase, nitrate reductase, glutamine synthetase, and glutamate synthase were significantly increased. Transcriptome analysis revealed that a total of 454 (65 up-regulated and 389 down-regulated) and 348 (293 up-regulated and 55 down-regulated) DEGs were observed when the roots under salt stress were treated with histidine for 12 h and 24 h, respectively. The pathways analysis of those DEGs showed that a small number of down-regulated genes were enriched in phytohormone signaling and phenylpropanoid biosynthesis at 12 h after histidine treatment, and the DEGs involved in the phytohormone signaling, glycolysis, and nitrogen metabolism were significantly enriched at 24 h after treatment. These results of gene expression and enzyme activities suggested that histidine can improve the salt tolerance of maize roots by enriching some DEGs involved in plant hormone signal transduction, glycolysis, and nitrogen metabolism pathways.

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.

Genome-Wide Identification and Characterization of the SBP Gene Family in Passion Fruit (Passiflora edulis Sims)

The SQUAMOSA promoter binding proteins (SBPs) gene family plays important roles in plant growth and development. The SBP gene family has been identified and reported in many species, but it has not been well studied in passion fruit. In this study, a total of 14 SBP genes were identified in passion fruit and named from PeSBP1 to PeSBP14 based on their chromosomal distribution. The phylogenetic tree, gene structure, conserved motifs, collinearity analysis, and expression patterns of the identified SBP members were analyzed. We classified the PeSBP genes into eight groups (I to VIII) according to the phylogenetic tree, gene structure, and conserved motifs. Synteny analysis found that 5 homologous gene pairs existed in PeSBP genes and 11 orthologous gene pairs existed between passion fruit and Arabidopsis. Synonymous nucleotide substitution analysis showed that the PeSBP genes were under strong negative selection. The expression pattern of PeSBP genes in seed, root, leaf, and flower showed that nine of the PeSBP genes displayed high expression in the leaf and the flower. The expression patterns of PeSBP3/6/8/9/10 were further detected by qRT-PCR. In addition, differences in the expression levels occurred for each gene in the different flower organs and at the different developmental stages. There were large differences among SBPs based on transcriptional levels under cold, heat, salt, and osmotic stress conditions. Altogether, this study provides an overview of SBP genes in passion fruit and lays the foundation for further functional analysis.

Cloning and Functional Analysis of NoMYB60 Gene Involved in Flavonoid Biosynthesis in Watercress (Nasturtium officinale R. Br.)

The MYB60 gene belongs to the R2R3-MYB subfamily, which includes the MYB31/30/96/94 genes. Although these genes have been shown to respond to heat and drought stresses, their role in flavonoid synthesis remains unclear. In this study, NoMYB60 was cloned from watercress and its structure and function were analyzed. Sequence structure analysis showed that NoMYB60 had a highly conserved R2R3 DNA-binding region at the N-terminus. Under the treatment of ABA, SA or MeJA, the expression level of NoMYB60 first significantly increased and then decreased, indicating that ABA, SA and MeJA positively regulated NoMYB60. The subcellular localization of NoMYB60-GFP indicated that NoMYB60 was localized in the nuclear region, which is consistent with the molecular characterization of the transcription factor. Gene silencing experiments were also performed to further test the function of NoMYB60. The result showed that virus-induced silencing of NoMYB60 affected the expression of enzyme genes in flavonoid synthesis pathways and promoted the synthesis of flavonoids. Moreover, we discovered that NoMYB60 interacts with NoBEH1/2. In this study, provides a reference for research on the regulation mechanism of flavonoid synthesis in Cruciferae and other crops.

Grapevine (Vitis vinifera) responses to salt stress and alkali stress: transcriptional and metabolic profiling

BACKGROUND

Soil salinization and alkalization are widespread environmental problems that limit grapevine (Vitis vinifera L.) growth and yield. However, little is known about the response of grapevine to alkali stress. This study investigated the differences in physiological characteristics, chloroplast structure, transcriptome, and metabolome in grapevine plants under salt stress and alkali stress.

RESULTS

We found that grapevine plants under salt stress and alkali stress showed leaf chlorosis, a decline in photosynthetic capacity, a decrease in chlorophyll content and Rubisco activity, an imbalance of Na⁺ and K⁺, and damaged chloroplast ultrastructure. Fv/Fm decreased under salt stress and alkali stress. NPQ increased under salt stress whereas decreased under alkali stress. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment showed the differentially expressed genes (DEGs) induced by salt stress and alkali stress were involved in different biological processes and have varied molecular functions. The expression of stress genes involved in the ABA and MAPK signaling pathways was markedly altered by salt stress and alkali stress. The genes encoding ion transporter (AKT1, HKT1, NHX1, NHX2, TPC1A, TPC1B) were up-regulated under salt stress and alkali stress. Down-regulation in the expression of numerous genes in the 'Porphyrin and chlorophyll metabolism', 'Photosynthesis-antenna proteins', and 'Photosynthesis' pathways were observed under alkali stress. Many genes in the 'Carbon fixation in photosynthetic organisms' pathway in salt stress and alkali stress were down-regulated. Metabolome showed that 431 and 378 differentially accumulated metabolites (DAMs) were identified in salt stress and alkali stress, respectively. L-Glutamic acid and 5-Aminolevulinate involved in chlorophyll synthesis decreased under salt stress and alkali stress. The abundance of 19 DAMs under salt stress related to photosynthesis decreased. The abundance of 16 organic acids in salt stress and 22 in alkali stress increased respectively.

CONCLUSIONS

Our findings suggested that alkali stress had more adverse effects on grapevine leaves, chloroplast structure, ion balance, and photosynthesis than salt stress. Transcriptional and metabolic profiling showed that there were significant differences in the effects of salt stress and alkali stress on the expression of key genes and the abundance of pivotal metabolites in grapevine plants.

AtbZIP62 Acts as a Transcription Repressor to Positively Regulate ABA Responses in Arabidopsis

The basic region/leucine zipper (bZIP) transcription factor AtbZIP62 is involved in the regulation of plant responses to abiotic stresses, including drought and salinity stresses, NO₃ transport, and basal defense in Arabidopsis. It is unclear if it plays a role in regulating plant responses to abscisic acid (ABA), a phytohormone that can regulate plant abiotic stress responses via regulating downstream ABA-responsive genes. Using RT-PCR analysis, we found that the expression level of AtbZIP62 was increased in response to exogenously applied ABA. Protoplast transfection assays show that AtbZIP62 is predominantly localized in the nucleus and functions as a transcription repressor. To examine the roles of AtbZIP62 in regulating ABA responses, we generated transgenic Arabidopsis plants overexpressing AtbZIP62 and created gene-edited atbzip62 mutants using CRISPR/Cas9. We found that in both ABA-regulated seed germination and cotyledon greening assays, the 35S:AtbZIP62 transgenic plants were hypersensitive, whereas atbzip62 mutants were hyposensitive to ABA. To examine the functional mechanisms of AtbZIP62 in regulating ABA responses, we generated Arabidopsis transgenic plants overexpressing 35S:AtbZIP62-GR, and performed transcriptome analysis to identify differentially expressed genes (DEGs) in the presence and absence of DEX, and found that DEGs are highly enriched in processes including response to abiotic stresses and response to ABA. Quantitative RT-PCR results further show that AtbZIP62 may regulate the expression of several ABA-responsive genes, including USP, ABF2, and SnRK2.7. In summary, our results show that AtbZIP62 is an ABA-responsive gene, and AtbZIP62 acts as a transcription repressor to positively regulate ABA responses in Arabidopsis.

Transcriptome analysis of response strategy in Hemerocallis fulva under drought stress

BACKGROUND

Hemerocallis fulva is an important ground cover plant widely used in urban greening. The analysis of the molecular mechanism underlying the drought response of H. fulva can lay a foundation for improving its adaptability and expanding its planting area.

OBJECTIVE

To reveal the drought response mechanisms of H. fulva, identify candidate unigenes associated with drought response, and lay a foundation for further unigenes functional study and drought resistance improvement of H. fulva via genetic engineering.

METHODS

RNA was isolated from H. fulva under different experimental conditions. De novo transcriptomic analysis of the samples was performed to screen drought response unigenes. The transcriptional changes of candidate drought response unigenes were verified by quantitative real-time PCR.

RESULTS

The differentially expressed unigenes and their functions were analyzed after H. fulva treated by PEG-simulated drought stress and rewatering. The candidate unigenes, associated with H. fulva drought response, were identified after transcriptome analysis. Then, the transcription level of drought response unigenes of H. fulva under different conditions was further verified. Abscisic acid, protein phosphorylation, sterol biosynthesis and ion transport were involved in drought response with quick restore in H. fulva. The response unigenes, involved in hormone (ABA, JA, CK and GA) signaling pathways, defense response, high light response, karrikin response and leaf shaping, can maintain at changed expression levels even after stress withdraw.

CONCLUSION

Hemerocallis fulva has unique drought response mechanism. Negative regulation mechanism may play more important roles in drought response of H. fulva. The analysis of candidate unigenes, associated with drought response, lays a foundation for further drought resistance improvement of H. fulva.

The Arabidopsis IDD14 transcription factor interacts with bZIP-type ABFs/AREBs and cooperatively regulates ABA-mediated drought tolerance

The INDETERMINATE DOMAIN (IDD) transcription factors mediate various aspects of plant growth and development. We previously reported that an Arabidopsis IDD subfamily regulates spatial auxin accumulation, and thus organ morphogenesis and gravitropic responses. However, its functions in stress responses are not well defined. Here, we use a combination of physiological, biochemical, molecular, and genetic approaches to provide evidence that the IDD14 cooperates with basic leucine zipper-type binding factors/ABA-responsive element (ABRE)-binding proteins (ABRE-binding factors (ABFs)/AREBs) in ABA-mediated drought tolerance. idd14-1D, a gain-of-function mutant of IDD14, exhibits decreased leaf water loss and improved drought tolerance, whereas inactivation of IDD14 in idd14-1 results in increased transpiration and reduced drought tolerance. Altered IDD14 expression affects ABA sensitivity and ABA-mediated stomatal closure. IDD14 can physically interact with ABF1-4 and subsequently promote their transcriptional activities. Moreover, ectopic expression and mutation of ABFs could, respectively, suppress and enhance plant sensitivity to drought stress in the idd14-1 mutant. Our results demonstrate that IDD14 forms a functional complex with ABFs and positively regulates drought-stress responses, thus revealing a previously unidentified role of IDD14 in ABA signaling and drought responses.