The E3 ligase TaGW2 mediates transcription factor TaARR12 degradation to promote drought resistance in wheat.

Drought stress limits crop yield, but the molecular modulators and their mechanisms underlying the trade-off between drought resistance and crop growth and development remain elusive. Here, a grain width and weight2 (GW2)-like really interesting new gene finger E3 ligase, TaGW2, was identified as a pivotal regulator of both kernel development and drought responses in wheat (Triticum aestivum). TaGW2 overexpression enhances drought resistance but leads to yield drag under full irrigation conditions. In contrast, TaGW2 knockdown or knockout attenuates drought resistance but remarkably increases kernel size and weight. Furthermore, TaGW2 directly interacts with and ubiquitinates the type-B Arabidopsis response regulator TaARR12, promoting its degradation via the 26S proteasome. Analysis of TaARR12 overexpression and knockdown lines indicated that TaARR12 represses the drought response but does not influence grain yield in wheat. Further DNA affinity purification sequencing combined with transcriptome analysis revealed that TaARR12 downregulates stress-responsive genes, especially group-A basic leucine zipper (bZIP) genes, resulting in impaired drought resistance. Notably, TaARR12 knockdown in the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated tagw2 knockout mutant leads to significantly higher drought resistance and grain yield compared to wild-type plants. Collectively, these findings show that the TaGW2-TaARR12 regulatory module is essential for drought responses, providing a strategy for improving stress resistance in high-yield wheat varieties.

Natural variation in a K+ -preferring HKT transporter contributes to wheat shoot K+ accumulation and salt tolerance.

Soil salinity can adversely affect crop growth and yield, and an improved understanding of the genetic factors that confer salt tolerance could inform breeding strategies to engineer salt-tolerant crops and improve productivity. Here, a group of K+ -preferring HKT transporters, TaHKT8, TaHKT9 and TaHKT10, were identified and negatively regulate the wheat shoot K+ accumulation and salt tolerance. A genome-wide association study (GWAS) and candidate gene association analysis further revealed that TaHKT9-B substantially underlies the natural variation of wheat shoot K+ accumulation under saline soil conditions. Specifically, an auxin responsive element (ARE) within an 8-bp insertion in the promoter of TaHKT9-B is strongly associated with shoot K+ content among wheat accessions. This ARE can be directly bound by TaARF4 for transcriptional activation of TaHKT9-B, which subsequently attenuates shoot K+ accumulation and salt tolerance. Moreover, the tae-miR390/TaTAS3/TaARF4 pathway was identified to regulate the salt-induced root development and salt tolerance in wheat. Taken together, our study describes the genetic basis and accompanying mechanism driving phenotypic variation in wheat shoot K+ accumulation and salt tolerance. The identified tae-miR390/TaTAS3/TaARF4/TaHKT9-B module is an important regulator in wheat subjected to salt stress, which provides the potentially important genetic resources for breeders to improve wheat salt tolerance.

Wheat adaptation to environmental stresses under climate change: Molecular basis and genetic improvement.

Wheat (Triticum aestivum) is a staple food for about 40% of the world's population. As the global population has grown and living standards improved, high yield and improved nutritional quality have become the main targets for wheat breeding. However, wheat production has been compromised by global warming through the more frequent occurrence of extreme temperature events, which have increased water scarcity, aggravated soil salinization, caused plants to be more vulnerable to diseases, and directly reduced plant fertility and suppressed yield. One promising option to address these challenges is the genetic improvement of wheat for enhanced resistance to environmental stress. Several decades of progress in genomics and genetic engineering has tremendously advanced our understanding of the molecular and genetic mechanisms underlying abiotic and biotic stress responses in wheat. These advances have heralded what might be considered a "golden age" of functional genomics for the genetic improvement of wheat. Here, we summarize the current knowledge on the molecular and genetic basis of wheat resistance to abiotic and biotic stresses, including the QTLs/genes involved, their functional and regulatory mechanisms, and strategies for genetic modification of wheat for improved stress resistance. In addition, we also provide perspectives on some key challenges that need to be addressed.

Duplicate Genes Contribute to Variability in Abiotic Stress Resistance in Allopolyploid Wheat.

Gene duplication is a universal biological phenomenon that drives genomic variation and diversity, plays a crucial role in plant evolution, and contributes to innovations in genetic engineering and crop development. Duplicated genes participate in the emergence of novel functionality, such as adaptability to new or more severe abiotic stress resistance. Future crop research will benefit from advanced, mechanistic understanding of the effects of gene duplication, especially in the development and deployment of high-performance, stress-resistant, elite wheat lines. In this review, we summarize the current knowledge of gene duplication in wheat, including the principle of gene duplication and its effects on gene function, the diversity of duplicated genes, and how they have functionally diverged. Then, we discuss how duplicated genes contribute to abiotic stress response and the mechanisms of duplication. Finally, we have a future prospects section that discusses the direction of future efforts in the short term regarding the elucidation of replication and retention mechanisms of repetitive genes related to abiotic stress response in wheat, excellent gene function research, and practical applications.

Differential alternative polyadenylation of homoeologous genes of allohexaploid wheat ABD subgenomes during drought stress response.

Because allohexaploid wheat genome contains ABD subgenomes, how the expression of homoeologous genes is coordinated remains largely unknown, particularly at the co-transcriptional level. Alternative polyadenylation (APA) is an important part of co-transcriptional regulation, which is crucial in developmental processes and stress responses. Drought stress is a major threat to the stable yield of wheat. Focusing on APA, we used poly(A) tag sequencing to track poly(A) site dynamics in wheat under drought stress. The results showed that drought stress led to extensive APA involving 37-47% of differentially expressed genes in wheat. Significant poly(A) site switching was found in stress-responsive genes. Interestingly, homoeologous genes exhibit unequal numbers of poly(A) sites, divergent APA patterns with tissue specificity and time-course dynamics, and distinct 3'-UTR length changes. Moreover, differentially expressed transcripts in leaves and roots used different poly(A) signals, the up- and downregulated isoforms had distinct preferences for non-canonical poly(A) sites. Genes that encode key polyadenylation factors showed differential expression patterns under drought stress. In summary, poly(A) signals and the changes in core poly(A) factors may widely affect the selection of poly(A) sites and gene expression levels during the response to drought stress, and divergent APA patterns among homoeologous genes add extensive plasticity to this responsive network. These results not only reveal the significant role of APA in drought stress response, but also provide a fresh perspective on how homoeologous genes contribute to adaptability through transcriptome diversity. In addition, this work provides information about the ends of transcripts for a better annotation of the wheat genome.

TaERF87 and TaAKS1 synergistically regulate TaP5CS1/TaP5CR1-mediated proline biosynthesis to enhance drought tolerance in wheat.

Drought stress limits wheat production and threatens food security world-wide. While ethylene-responsive factors (ERFs) are known to regulate plant response to drought stress, the regulatory mechanisms responsible for a tolerant phenotype remain unclear. Here, we describe the positive regulatory role of TaERF87 in mediating wheat tolerance to drought stress. TaERF87 overexpression (OE) enhances drought tolerance, while silencing leads to drought sensitivity in wheat. RNA sequencing with biochemical assays revealed that TaERF87 activates the expression of the proline biosynthesis genes TaP5CS1 and TaP5CR1 via direct binding to GCC-box elements. Furthermore, proline accumulates to higher levels in TaERF87- and TaP5CS1-OE lines than that in wild-type plants under well-watered and drought stress conditions concomitantly with enhanced drought tolerance in these transgenic lines. Moreover, the interaction between TaERF87 and the bHLH transcription factor TaAKS1 synergistically enhances TaP5CS1 and TaP5CR1 transcriptional activation. TaAKS1 OE also increases wheat drought tolerance by promoting proline accumulation. Additionally, our findings verified that TaERF87 and TaAKS1 are targets of abscisic acid-responsive element binding factor 2 (TaABF2). Together, our study elucidates the mechanisms underlying a positive response to drought stress mediated by the TaABF2-TaERF87/TaAKS1-TaP5CS1/TaP5CR1 module, and identifies candidate genes for the development of elite drought-tolerant wheat varieties.

A gain-of-function allele of a DREB transcription factor gene ameliorates drought tolerance in wheat.

Drought is a major environmental factor limiting wheat production worldwide. However, the genetic components underlying wheat drought tolerance are largely unknown. Here, we identify a DREB transcription factor gene (TaDTG6-B) by genome-wide association study that is tightly associated with drought tolerance in wheat. Candidate gene association analysis revealed that a 26-bp deletion in the TaDTG6-B coding region induces a gain-of-function for TaDTG6-BDel574, which exhibits stronger transcriptional activation, protein interactions, and binding activity to dehydration-responsive elements (DRE)/CRT cis-elements than the TaDTG6-BIn574 encoded by the allele lacking the deletion, thus conferring greater drought tolerance in wheat seedlings harboring this variant. Knockdown of TaDTG6-BDel574 transcripts attenuated drought tolerance in transgenic wheat, whereas its overexpression resulted in enhanced drought tolerance without accompanying phenotypic abnormalities. Furthermore, the introgression of the TaDTG6-BDel574 elite allele into drought-sensitive cultivars improved their drought tolerance, thus providing a valuable genetic resource for wheat breeding. We also identified 268 putative target genes that are directly bound and transcriptionally regulated by TaDTG6-BDel574. Further analysis showed that TaDTG6-BDel574 positively regulates TaPIF1 transcription to enhance wheat drought tolerance. These results describe the genetic basis and accompanying mechanism driving phenotypic variation in wheat drought tolerance, and provide a novel genetic resource for crop breeding programs.

Genome-wide association study revealed TaHXK3-2A as a candidate gene controlling stomatal index in wheat seedlings.

Stomata are important channels for the control of gas exchange between plants and the atmosphere. To examine the genetic architecture of wheat stomatal index, we performed a genome-wide association study (GWAS) using a panel of 539 wheat accessions and 450 678 polymorphic single nucleotide polymorphisms (SNPs) that were detected using wheat-specific 660K SNP array. A total of 130 SNPs were detected to be significantly associated with stomatal index in both leaf surfaces of wheat seedlings. These significant SNPs were distributed across 16 chromosomes and involved 2625 candidate genes which participate in stress response, metabolism and cell/organ development. Subsequent bulk segregant analysis (BSA), combined with GWAS identified one major haplotype on chromosome 2A, that is responsible for stomatal index on the abaxial leaf surface. Candidate gene association analysis revealed that genetic variation in the promoter region of the hexokinase gene TaHXK3-2A was significantly associated with the stomatal index. Moreover, transgenic analysis confirmed that TaHXK3-2A overexpression in wheat decreased the size of leaf pavement cells but increased stomatal density through the glucose metabolic pathway, resulting in drought sensitivity among TaHXK3-2A transgenic lines due to an increased transpiration rate. Taken together, these results provide valuable insights into the genetic control of the stomatal index in wheat seedlings.

The miR319/TaGAMYB3 module regulates plant architecture and improves grain yield in common wheat (Triticum aestivum).

Plant architecture is a key determinant of crop productivity and adaptation. The highly conserved microRNA319 (miR319) family functions in various biological processes, but little is known about how miR319 regulates plant architecture in wheat (Triticum aestivum). Here, we determined that the miR319/TaGAMYB3 module controls plant architecture and grain yield in common wheat. Repressing tae-miR319 using short tandem target mimics resulted in favorable plant architecture traits, including increased plant height, reduced tiller number, enlarged spikes and flag leaves, and thicker culms, as well as enhanced grain yield in field plot tests. Overexpressing tae-miR319 had the opposite effects on plant architecture and grain yield. Although both TaPCF8 and TaGAMYB3 were identified as miR319 target genes, genetic complementation assays demonstrated that only miR319-resistant TaGAMYB3 (rTaGAMYB3) abolished tae-miR319-mediated growth inhibition of flag leaves and spikes. TaGAMYB3 functions as a transcriptional activator of downstream genes, including TaPSKR1, TaXTH23, TaMADS5 and TaMADS51, by binding to their promoters. Furthermore, TaGAMYB3 physically interacts with TaBA1, an important regulator of spike development, to additively activate the transcription of downstream genes such as TaMADS5. Our findings provide insight into how the miR319/TaGAMYB3 module regulates plant architecture and improves grain yield in common wheat.

Genome-wide analysis of trehalose-6-phosphate phosphatases (TPP) gene family in wheat indicates their roles in plant development and stress response.

BACKGROUND: Trehalose-6-phosphate phosphatases genes (TPPs) are involved in the development and stress response of plants by regulating the biosynthesis of trehalose, though little is currently known about TPPs in common wheat (Triticum aestivum L.). RESULTS: In this study, we performed a genome-wide identification of the TPP gene family in common wheat, and identified a total of 31 TaTPP genes. These were subdivided into six subfamilies based on the phylogenetic relationships and the conservation of protein in six monocot and eudicot plants. The majority of TPP genes were represented by 2-3 wheat homoalleles (named TaTPPX_ZA, TaTPPX_ZB, or TaTPPX_ZD), where Z is the location on the wheat chromosome of the gene number (X). We also analyzed the chromosomal location, exon-intron structure, orthologous genes, and protein motifs of the TaTPPs. The RNA-seq data was used to perform an expression analysis, which found 26 TaTPP genes to be differentially expressed based on spatial and temporal characteristics, indicating they have varied functions in the growth and development of wheat. Additionally, we assessed how the promoter regulatory elements were organized and used qRT-PCR in the leaves to observe how they were expressed following ABA, salt, low tempreture, and drought stress treatments. All of these genes exhibited differential expression against one or more stress treatments. Furthermore, ectopic expression of TaTPP11 in Arabidopsis exhibited a phenotype that delayed plant development but did not affect seed morphology. CONCLUSIONS: TaTPPs could serve important roles in the development and stress response in wheat. These results provide a basis for subsequent research into the function of TaTPPs.

The wheat ABA receptor gene TaPYL1-1B contributes to drought tolerance and grain yield by increasing water-use efficiency.

The role of abscisic acid (ABA) receptors, PYR1/PYL/RCAR (PYLs), is well established in ABA signalling and plant drought response, but limited research has explored the regulation of wheat PYLs in this process, especially the effects of their allelic variations on drought tolerance or grain yield. Here, we found that the overexpression of a TaABFs-regulated PYL gene, TaPYL1-1B, exhibited higher ABA sensitivity, photosynthetic capacity and water-use efficiency (WUE), all contributed to higher drought tolerance than that of wild-type plants. This heightened water-saving mechanism further increased grain yield and protected productivity during water deficit. Candidate gene association analysis revealed that a favourable allele TaPYL1-1BIn-442 , carrying an MYB recognition site insertion in the promoter, is targeted by TaMYB70 and confers enhanced expression of TaPYL1-1B in drought-tolerant genotypes. More importantly, an increase in frequency of the TaPYL1-1BIn-442 allele over decades among modern Chinese cultivars and its association with high thousand-kernel weight together demonstrated that it was artificially selected during wheat improvement efforts. Taken together, our findings illuminate the role of TaPYL1-1B plays in coordinating drought tolerance and grain yield. In particular, the allelic variant TaPYL1-1BIn-442 substantially contributes to enhanced drought tolerance while maintaining high yield, and thus represents a valuable genetic target for engineering drought-tolerant wheat germplasm.

Variation in cis-regulation of a NAC transcription factor contributes to drought tolerance in wheat.

Drought is a major environmental factor limiting wheat production worldwide, and developing drought-tolerant cultivars is a central challenge for wheat breeders globally. Therefore, it is important to identify genetic components determining drought tolerance in wheat. In this study, we identified a wheat NAC gene (TaNAC071-A) that is tightly associated with drought tolerance by a genome-wide association study. Knockdown of TaNAC071-A in wheat attenuated plant drought tolerance, whereas its overexpression significantly enhanced drought tolerance through improved water-use efficiency and increased expression of stress-responsive genes. This heightened water-saving mechanism mitigated the yield loss caused by water deficit. Further candidate gene association analysis showed that a 108-bp insertion in the promoter of TaNAC071-A alters its expression level and contributes to variation in drought tolerance among wheat accessions. This insertion contains two MYB cis-regulatory elements (CREs) that can be directly bound by the MYB transcription activator, TaMYBL1, thereby leading to increased TaNAC071-A expression and plant drought tolerance. Importantly, introgression of this 108-bp insertion allele, TaNAC071-AIn-693, into drought-sensitive cultivars could improve their drought tolerance, demonstrating that it is a valuable genetic resource for wheat breeding. Taken together, our findings highlight a major breakthrough in determining the genetic basis underlying phenotypic variation in wheat drought tolerance and showcase the potential of exploiting CRE-containing indels for improving important agronomical traits.

A Deep Learning-Based Method for Automatic Assessment of Stomatal Index in Wheat Microscopic Images of Leaf Epidermis.

The stomatal index of the leaf is the ratio of the number of stomata to the total number of stomata and epidermal cells. Comparing with the stomatal density, the stomatal index is relatively constant in environmental conditions and the age of the leaf and, therefore, of diagnostic characteristics for a given genotype or species. Traditional assessment methods involve manual counting of the number of stomata and epidermal cells in microphotographs, which is labor-intensive and time-consuming. Although several automatic measurement algorithms of stomatal density have been proposed, no stomatal index pipelines are currently available. The main aim of this research is to develop an automated stomatal index measurement pipeline. The proposed method employed Faster regions with convolutional neural networks (R-CNN) and U-Net and image-processing techniques to count stomata and epidermal cells, and subsequently calculate the stomatal index. To improve the labeling speed, a semi-automatic strategy was employed for epidermal cell annotation in each micrograph. Benchmarking the pipeline on 1,000 microscopic images of leaf epidermis in the wheat dataset (Triticum aestivum L.), the average counting accuracies of 98.03 and 95.03% for stomata and epidermal cells, respectively, and the final measurement accuracy of the stomatal index of 95.35% was achieved. R 2 values between automatic and manual measurement of stomata, epidermal cells, and stomatal index were 0.995, 0.983, and 0.895, respectively. The average running time (ART) for the entire pipeline could be as short as 0.32 s per microphotograph. The proposed pipeline also achieved a good transferability on the other families of the plant using transfer learning, with the mean counting accuracies of 94.36 and 91.13% for stomata and epidermal cells and the stomatal index accuracy of 89.38% in seven families of the plant. The pipeline is an automatic, rapid, and accurate tool for the stomatal index measurement, enabling high-throughput phenotyping, and facilitating further understanding of the stomatal and epidermal development for the plant physiology community. To the best of our knowledge, this is the first deep learning-based microphotograph analysis pipeline for stomatal index assessment.

Overexpression of the wheat NAC transcription factor TaSNAC4-3A gene confers drought tolerance in transgenic Arabidopsis.

NAC transcription factors (TFs) play critical roles in plant abiotic stress responses. However, information on the roles of NAC TFs is limited in wheat (Triticum aestivum L.). In this study, we isolated three wheat TaSNAC4 homeologous genes, TaSNAC4-3A, TaSNAC4-3B, and TaSNAC4-3D, and characterized the function of TaSNAC4-3A in plant drought tolerance. TaSNAC4 is highly expressed in seedling leaves, and expression is induced by various abiotic stresses. Transient expression and transactivation assays showed that TaSNAC4-3A is localized to the nucleus, and the C-terminal region has transcriptional activation activity. Overexpression of TaSNAC4-3A in Arabidopsis led to stimulated germination and root growth when exposed to salt and osmotic stresses, and drought stress tolerance was significantly increased in the TaSNAC4-3A transgenic lines. When compared to the control plants, the transgenic lines overexpressing TaSNAC4-3A exhibited reduced stomatal aperture size under drought stress, and therefore had lower water loss rates. In addition, the overexpression of TaSNAC4-3A led to abscisic acid (ABA) hypersensitivity at the root elongation and seed germination stages. Further transcriptomic analysis demonstrated that there was a significant up-regulation of stress responsive genes in the TaSNAC4-3A transgenic lines. Our findings have revealed the important role of TaSNAC4-3A in plant drought tolerance.

Genome-wide analysis of the AREB/ABF gene lineage in land plants and functional analysis of TaABF3 in Arabidopsis.

BACKGROUND: Previous studies have shown that ABFs (abscisic acid-responsive transcription factors) are important ABA-signaling components that participate in abiotic stress response. However, little is known about the function of ABFs in Triticum aestivum. In addition, although various ABFs have been identified in other species, the phylogenetic relationship between ABF transcription factors has not been systemically investigated in land plants. RESULTS: In this study, we systemically collected ABFs from land plants and analyzed the phylogenetic relationship of these ABF genes. The ABF genes are present in all the land plants we investigated, including moss, lycophyte, monocots, and eudicots. Furthermore, these ABF genes are phylogenetically divided into seven subgroups, differentiations that are supported by variation in the gene structure, protein properties, and motif patterns. We further demonstrated that the expression of ABF genes varies among different tissues and developmental stages, and are induced by one or more environmental stresses. Furthermore, we found that three wheat ABFs (TaABF1, TaABF2, and TaABF3) were significantly induced by drought stress. Compared with wild-type (WT) plants, transgenic Arabidopsis plants overexpressing TaABF3 displayed enhanced drought tolerance. CONCLUSIONS: These results provide important ground work for understanding the phylogenetic relationships between plant ABF genes. Our results also indicate that TaABFs may participate in regulating plant response to abiotic stresses.

Characterization of wheat homeodomain-leucine zipper family genes and functional analysis of TaHDZ5-6A in drought tolerance in transgenic Arabidopsis.

BACKGROUND: Many studies in Arabidopsis and rice have demonstrated that HD-Zip transcription factors play important roles in plant development and responses to abiotic stresses. Although common wheat (Triticum aestivum L.) is one of the most widely cultivated and consumed food crops in the world, the function of the HD-Zip proteins in wheat is still largely unknown. RESULTS: To explore the potential biological functions of HD-Zip genes in wheat, we performed a bioinformatics and gene expression analysis of the HD-Zip family. We identified 113 HD-Zip members from wheat and classified them into four subfamilies (I-IV) based on phylogenic analysis against proteins from Arabidopsis, rice, and maize. Most HD-Zip genes are represented by two to three homeoalleles in wheat, which are named as TaHDZX_ZA, TaHDZX_ZB, or TaHDZX_ZD, where X denotes the gene number and Z the wheat chromosome on which it is located. TaHDZs in the same subfamily have similar protein motifs and intron/exon structures. The expression profiles of TaHDZ genes were analysed in different tissues, at different stages of vegetative growth, during seed development, and under drought stress. We found that most TaHDZ genes, especially those in subfamilies I and II, were induced by drought stress, suggesting the potential importance of subfamily I and II TaHDZ members in the responses to abiotic stress. Compared with wild-type (WT) plants, transgenic Arabidopsis plants overexpressing TaHDZ5-6A displayed enhanced drought tolerance, lower water loss rates, higher survival rates, and higher proline content under drought conditions. Additionally, the transcriptome analysis identified a number of differentially expressed genes between 35S::TaHDZ5-6A transgenic and wild-type plants, many of which are involved in stress response. CONCLUSIONS: Our results will facilitate further functional analysis of wheat HD-Zip genes, and also indicate that TaHDZ5-6A may participate in regulating the plant response to drought stress. Our experiments show that TaHDZ5-6A holds great potential for genetic improvement of abiotic stress tolerance in crops.

Genetic variation in ZmTIP1 contributes to root hair elongation and drought tolerance in maize.

Drought is a major abiotic stress that threatens maize production globally. A previous genome-wide association study identified a significant association between the natural variation of ZmTIP1 and the drought tolerance of maize seedlings. Here, we report on comprehensive genetic and functional analysis, indicating that ZmTIP1, which encodes a functional S-acyltransferase, plays a positive role in regulating the length of root hairs and the level of drought tolerance in maize. We show that enhancing ZmTIP1 expression in transgenic Arabidopsis and maize increased root hair length, as well as plant tolerance to water deficit. In contrast, ZmTIP1 transposon-insertional mutants displayed the opposite phenotype. A calcium-dependent protein kinase, ZmCPK9, was identified as a substrate protein of ZmTIP1, and ZmTIP1-mediated palmitoylation of two cysteine residues facilitated the ZmCPK9 PM association. The results of this research enrich our knowledge about ZmTIP1-mediated protein S-acylation modifications in relation to the regulation of root hair elongation and drought tolerance. Additionally, the identification of a favourable allele of ZmTIP1 also provides a valuable genetic resource or selection target for the genetic improvement of maize.

Regulatory changes in TaSNAC8-6A are associated with drought tolerance in wheat seedlings.

Wheat is a staple crop produced in arid and semi-arid areas worldwide, and its production is frequently compromised by water scarcity. Thus, increased drought tolerance is a priority objective for wheat breeding programmes, and among their targets, the NAC transcription factors have been demonstrated to contribute to plant drought response. However, natural sequence variations in these genes have been largely unexplored for their potential roles in drought tolerance. Here, we conducted a candidate gene association analysis of the stress-responsive NAC gene subfamily in a wheat panel consisting of 700 varieties collected worldwide. We identified a drought responsive gene, TaSNAC8-6A, that is tightly associated with drought tolerance in wheat seedlings. Further analysis found that a favourable allele TaSNAC8-6AIn-313 , carrying an insertion in the ABRE promoter motif, is targeted by TaABFs and confers enhanced drought-inducible expression of TaSNAC8-6A in drought-tolerant genotypes. Transgenic wheat and Arabidopsis TaSNAC8-6A overexpression lines exhibited enhanced drought tolerance through induction of auxin- and drought-response pathways, confirmed by transcriptomic analysis, that stimulated lateral root development, subsequently improving water-use efficiency. Taken together, our findings reveal that natural variation in TaSNAC8-6A and specifically the TaSNAC8-6AIn-313 allele strongly contribute to wheat drought tolerance and thus represent a valuable genetic resource for improvement of drought-tolerant germplasm for wheat production.

Global transcriptome analysis uncovers the gene co-expression regulation network and key genes involved in grain development of wheat (Triticum aestivum L.).

Wheat grain development is a robust biological process that largely determines grain quality and yield. In this study, we investigated the grain transcriptome of winter wheat cv. Xiaoyan-6 at four developmental stages (5, 10, 15, and 20 days post-anthesis), using high-throughput RNA sequencing (RNA-Seq). We identified 427 grain-specific transcription factors (TFs) and 1653 differentially expressed TFs during grain development as well as a grain co-expression regulation network (GrainNet) of the TFs and their predicted co-expressed genes. Our study identified ten putative key TFs and the predicted regulatory genes of these TFs in wheat grain development of Xiaoyan-6. The analysis was given a firm basis through the study of additional wheat tissues, including root, stem, leaf, flag leaf, grain, spikes (from wheat plants at booting or heading stages) to provide a dataset of 92,478 high-confidence protein-coding genes that were mostly evenly distributed among subgenomes, but unevenly distributed across each of the chromosomes or each of the seven homeologous groups. Within this larger framework of the transcriptomes, we identified 4659 grain-specific genes (SEGs) and 26,500 differentially expressed genes (DEGs) throughout grain development stages tested. The SEGs identified mainly associate with regulation and signaling-related biological processes, while the DEGs mainly involve in cellular component organization or biogenesis and nutrient reservoir activity during grain development of Xiaoyan-6. This study establishes new targets for modifying genes related to grain development and yield, to fine-tune expression in different varieties and environments.