Deciphering genetic basis of developmental and agronomic traits by integrating high-throughput optical phenotyping and genome-wide association studies in wheat.

Dissecting the genetic basis of complex traits such as dynamic growth and yield potential is a major challenge in crops. Monitoring the growth throughout growing season in a large wheat population to uncover the temporal genetic controls for plant growth and yield-related traits has so far not been explored. In this study, a diverse wheat panel composed of 288 lines was monitored by a non-invasive and high-throughput phenotyping platform to collect growth traits from seedling to grain filling stage and their relationship with yield-related traits was further explored. Whole genome re-sequencing of the panel provided 12.64 million markers for a high-resolution genome-wide association analysis using 190 image-based traits and 17 agronomic traits. A total of 8327 marker-trait associations were detected and clustered into 1605 quantitative trait loci (QTLs) including a number of known genes or QTLs. We identified 277 pleiotropic QTLs controlling multiple traits at different growth stages which revealed temporal dynamics of QTLs action on plant development and yield production in wheat. A candidate gene related to plant growth that was detected by image traits was further validated. Particularly, our study demonstrated that the yield-related traits are largely predictable using models developed based on i-traits and provide possibility for high-throughput early selection, thus to accelerate breeding process. Our study explored the genetic architecture of growth and yield-related traits by combining high-throughput phenotyping and genotyping, which further unravelled the complex and stage-specific contributions of genetic loci to optimize growth and yield in wheat.

Mapping Quantitative Trait Loci for Type II Fusarium Head Blight Resistance in Two Wheat Recombinant Inbred Line Populations Derived from Yangmai 4 and Yangmai 5.

Fusarium head blight (FHB) is a destructive wheat disease worldwide and significantly affects grain yield and quality in wheat. To understand the genetic basis underlying type II FHB resistance in two elite wheat cultivars-Yangmai 4 (YM4) and Yangmai 5 (YM5)-quantitative trait loci (QTL) mapping was conducted in two recombinant inbred line (RIL) populations derived from the crosses of YM4 and YM5 with susceptible cultivar Yanzhan 1 (YZ1), respectively. A survey with markers linked to Fhb1, Fhb2, Fhb4, and Fhb5 in landrace Wangshuibai indicated the nonexistence of these known FHB resistance genes or QTL in YM4, YM5, and YZ1. One overlapped resistance QTL was identified in both RIL populations (namely, QFhb.Y4.2D/QFhb.Y5.2D) with a large effect on FHB resistance. One novel resistance QTL (QFhb.Y4.5A) mapped on chromosome 5A was detected only in the YM4/YZ1 population. The resistance alleles of both QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A did not increase the plant height and did not significantly affect the heading date and flowering date. Kompetitive allele-specific PCR markers for QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A had been developed to verify in an additional set of 244 geographically diverse cultivars or lines. Pyramiding of the two resistance alleles decreased the percentage of symptomatic spikelets by 51.77% relative to the cultivars or lines without these two resistance alleles. QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A were shown to be useful alternatives in FHB resistance breeding programs. The results will facilitate marker-assisted selection for introgression of the favorable alleles for improving FHB resistance in breeding programs.

Helitron and CACTA DNA transposons actively reshape the common wheat - AK58 genome.

Transposable elements (TEs) play a pivotal role in reshaping the plant genome. Helitrons represent a new class of transposable elements recently discovered in animals and plants. Helitrons, DNA transposons that replicate via a rolling-circle replication mechanism, are a major driving force behind genome evolution. Since the recent divergence of the modern cultivars (e.g., AK58) and landraces (e.g., Chinese Spring), Helitrons appear to have contributed greatly to genome variability. We first identified 214,665 Helitrons in AK58 by HelitronScanner software and further detected 18,668 tandem duplicated Helitron regions (TDHRs) from all the Helitrons identified. There are 39% of TDHRs (7289) translocated since the divergence of the AK58 and Chinese Spring genomes. What interested us even more are the 462 TDHRs exclusive to the AK58 genome. We also found 235 TDHRs in the 21 centromeric regions and these TDHRs contributed to centromere plasticity. Another very interesting DNA transposon, CACTA, accounting for 15% of AK58 genome, was also the focus of this study because they often inserted into gene rich regions. We found that CACTAs have inserted into many agronomically important genes, such as seed dormancy gene TaMFT and vernalization gene TaVrn1, indicating the important role of CACTAs in modern wheat adaptation.

Epigenetic Landscape Is Largely Shaped by Diversiform Transposons in Aegilops tauschii.

Transposons (TEs) account for more than 80% of the wheat genome, the highest among all known crop species. They play an important role in shaping the elaborate genomic landscape, which is the key to the speciation of wheat. In this study, we analyzed the association between TEs, chromatin states, and chromatin accessibility in Aegilops tauschii, the D genome donor of bread wheat. We found that TEs contributed to the complex but orderly epigenetic landscape as chromatin states showed diverse distributions on TEs of different orders or superfamilies. TEs also contributed to the chromatin state and openness of potential regulatory elements, affecting the expression of TE-related genes. Some TE superfamilies, such as hAT-Ac, carry active/open chromatin regions. In addition, the histone mark H3K9ac was found to be associated with the accessibility shaped by TEs. These results suggest the role of diversiform TEs in shaping the epigenetic landscape and in gene expression regulation in Aegilops tauschii. This has positive implications for understanding the transposon roles in Aegilops tauschii or the wheat D genome.

Intra-Varietal Diversity and Its Contribution to Wheat Evolution, Domestication, and Improvement in Wheat.

Crop genetic diversity is essential for adaptation and productivity in agriculture. A previous study revealed that poor allele diversity in wheat commercial cultivars is a major barrier to its further improvement. Homologs within a variety, including paralogs and orthologs in polyploid, account for a large part of the total genes of a species. Homolog diversity, intra-varietal diversity (IVD), and their functions have not been elucidated. Common wheat, an important food crop, is a hexaploid species with three subgenomes. This study analyzed the sequence, expression, and functional diversity of homologous genes in common wheat based on high-quality reference genomes of two representative varieties, a modern commercial variety Aikang 58 (AK58) and a landrace Chinese Spring (CS). A total of 85,908 homologous genes, accounting for 71.9% of all wheat genes, including inparalogs (IPs), outparalogs (OPs), and single-copy orthologs (SORs), were identified, suggesting that homologs are an important part of the wheat genome. The levels of sequence, expression, and functional variation in OPs and SORs were higher than that of IPs, which indicates that polyploids have more homologous diversity than diploids. Expansion genes, a specific type of OPs, made a great contribution to crop evolution and adaptation and endowed crop with special characteristics. Almost all agronomically important genes were from OPs and SORs, demonstrating their essential functions for polyploid evolution, domestication, and improvement. Our results suggest that IVD analysis is a novel approach for evaluating intra-genomic variations, and exploitation of IVD might be a new road for plant breeding, especially for polyploid crops, such as wheat.

DIW1 encoding a clade I PP2C phosphatase negatively regulates drought tolerance by de-phosphorylating TaSnRK1.1 in wheat.

Drought seriously impacts wheat production (Triticum aestivum L.), while the exploitation and utilization of genes for drought tolerance are insufficient. Leaf wilting is a direct reflection of drought tolerance in plants. Clade A PP2Cs are abscisic acid (ABA) co-receptors playing vital roles in the ABA signaling pathway, regulating drought response. However, the roles of other clade PP2Cs in drought tolerance, especially in wheat, remain largely unknown. Here, we identified a gain-of-function drought-induced wilting 1 (DIW1) gene from the wheat Aikang 58 mutant library by map-based cloning, which encodes a clade I protein phosphatase 2C (TaPP2C158) with enhanced protein phosphatase activity. Phenotypic analysis of overexpression and CRISPR/Cas9 mutant lines demonstrated that DIW1/TaPP2C158 is a negative regulator responsible for drought resistance. We found that TaPP2C158 directly interacts with TaSnRK1.1 and de-phosphorylates it, thus inactivating the TaSnRK1.1-TaAREB3 pathway. TaPP2C158 protein phosphatase activity is negatively correlated with ABA signaling. Association analysis suggested that C-terminal variation of TaPP2C158 changing protein phosphatase activity is highly correlated with the canopy temperature, and seedling survival rate under drought stress. Our data suggest that the favorable allele with lower phosphatase activity of TaPP2C158 has been positively selected in Chinese breeding history. This work benefits us in understanding the molecular mechanism of wheat drought tolerance, and provides elite genetic resources and molecular markers for improving wheat drought tolerance.

A new major QTL for flag leaf thickness in barley (Hordeum vulgare L.).

BACKGROUND: Carbohydrate accumulation of photosynthetic organs, mainly leaves, are the primary sources of grain yield in cereals. The flag leaf plays a vital role in seed development, which is probably the most neglected morphological characteristic during traditional selection processes. RESULTS: In this experiment, four flag leaf morphological traits and seven yield-related traits were investigated in a DH population derived from a cross between a wild barley and an Australian malting barley cultivar. Flag leaf thickness (FLT) showed significantly positive correlations with grain size. Four QTL, located on chromosomes 1H, 2H, 3H, and 5H, respectively, were identified for FLT. Among them, a major QTL was located on chromosome 3H with a LOD value of 18.4 and determined 32% of the phenotypic variation. This QTL showed close links but not pleiotropism to the previously reported semi-dwarf gene sdw1 from the cultivated barley. This QTL was not reported before and the thick leaf allele from the wild barley could provide a useful source for improving grain yield through breeding. CONCLUSIONS: Our results also provided valuable evidence that source traits and sink traits in barley are tightly connected and suggest further improvement of barley yield potential with enhanced and balanced source and sink relationships by exploiting potentialities of the wild barley resources. Moreover, this study will provide a novel sight on understanding the evolution and development of leaf morphology in barley and improving barley production by rewilding for lost superior traits during plant evolution.

Leaf thickness of barley: genetic dissection, candidate genes prediction and its relationship with yield-related traits.

KEY MESSAGE: In this first genetic study on assessing leaf thickness directly in cereals, major and environmentally stable QTL were detected in barley and candidate genes underlying a major locus were identified. Leaf thickness (LT) is an important characteristic affecting leaf functions which have been intensively studied. However, as LT has a small dimension in many plant species and technically difficult to measure, previous studies on this characteristic are often based on indirect estimations. In the first study of detecting QTL controlling LT by directly measuring the characteristic in barley, large and stable loci were detected from both field and glasshouse trials conducted in different cropping seasons by assessing a population of 201 recombinant inbred lines. Four loci (locating on chromosome arms 2H, 3H, 5H and 6H, respectively) were consistently detected for flag leaf thickness (FLT) in each of these trials. The one on 6H had the largest effect, with a maximum LOD 9.8 explaining up to 20.9% of phenotypic variance. FLT does not only show strong interactions with flag leaf width and flag leaf area but has also strong correlations with fertile tiller number, spike row types, kernel number per spike and heading date. Though with reduced efficiency, these loci were also detectable from assessing second last leaf of fully grown plants or even from assessing the third leaves of seedlings. Taking advantage of the high-quality genome assemblies for both parents of the mapping population used in this study, three candidate genes underlying the 6H QTL were predicted based on orthologous analysis. These results do not only broaden our understanding on genetic basis of LT and its relationship with other traits in cereal crops but also form the bases for cloning and functional analysis of genes regulating LT in barley.

Genome-wide association study of agronomic traits related to nitrogen use efficiency in wheat.

KEY MESSAGE: GWAS identified 347 QTLs associated with eight traits related to nitrogen use efficiency in a 389-count wheat panel. Four novel candidate transcription factor genes were verified using qRT-PCR. Nitrogen is an essential nutrient for plants that determines crop yield. Improving nitrogen use efficiency (NUE) should considerably increase wheat yield and reduce the use of nitrogen fertilisers. However, knowledge on the genetic basis of NUE during wheat maturity is limited. In this study, a diversity panel incorporating 389 wheat accessions was phenotyped for eight NUE-related agronomic traits across five different environments. A total of 347 quantitative trait loci (QTLs) for low nitrogen tolerance indices (ratio of agronomic characters under low and high nitrogen conditions) were identified through a genome-wide association study utilising 397,384 single nucleotide polymorphisms (SNPs) within the MLM (Q + K) model, including 11 stable QTLs. Furthermore, 69 candidate genes were predicted for low nitrogen tolerance indices of best linear unbiased predictions values of the eight studied agronomic traits, and four novel candidate transcription factors (TraesCS5A02G237500 for qFsnR5A.2, TraesCS5B02G384500 and TraesCS5B02G384600 for qSLR5B.1, and TraesCS3B02G068800 for qTKWR3B.1) showed differing expression patterns in contrasting low-nitrogen-tolerant wheat genotypes. Moreover, the number of favourable marker alleles calculated using NUE that were significantly related to SNP in accessions decreased over the decades, indicating a decline in the NUE of the 389 wheat varieties. These findings denote promising NUE markers that could be useful in breeding high-NUE wheat varieties, and the candidate genes could further detail the NUE-related regulation network in wheat.

Identification of a novel ERF gene, TaERF8, associated with plant height and yield in wheat.

BACKGROUND: Ethylene Responsive Factor (ERF) is involved in various processes of plant development and stress responses. In wheat, several ERFs have been identified and their roles in mediating biotic or abiotic stresses have been elucidated. However, their effects on wheat plant architecture and yield-related traits remain poorly studied. RESULTS: In this study, TaERF8, a new member of the ERF family, was isolated in wheat (Triticum aestivum L.). Three homoeologous TaERF8 genes, TaERF8-2A, TaERF8-2B and TaERF8-2D (named according to sub-genomic origin), were cloned from the common wheat cultivar Chinese Spring. The three homoeologs showed highly similar protein sequences, with identical AP2 domain. Whereas homoeologs sequence polymorphism analysis allowed the establishment of ten, two and three haplotypes, respectively. Expression analysis revealed that TaERF8s were constitutively expressed through entire wheat developmental stages. Analysis of related agronomic traits of TaERF8-2B overexpressing transgenic lines showed that TaERF8-2B plays a role in regulating plant architecture and yield-related traits. Association analysis between TaERF8-2B haplotypes (Hap-2B-1 and Hap-2B-2) and agronomic traits showed that TaERF8-2B was associated with plant height, heading date and 1000 kernel weight (TKW). The TaERF8-2B haplotypes distribution analysis revealed that Hap-2B-2 frequency increased in domesticated emmer wheat and modern varieties, being predominant in five major China wheat producing zones. CONCLUSION: These results indicated that TaERF8s are differentially involved in the regulation of wheat growth and development. Haplotype Hap-2B-2 was favored during domestication and in Chinese wheat breeding. Unveiling that the here described molecular marker TaERF8-2B-InDel could be used for marker-assisted selection, plant architecture and TKW improvement in wheat breeding.

QTL mapping for yield-related traits in wheat based on four RIL populations.

KEY MESSAGE: Eight environmentally stable QTL for grain yield-related traits were detected by four RIL populations, and two of them were validated by a natural wheat population containing 580 diverse varieties or lines. Yield and yield-related traits are important factors in wheat breeding. In this study, four RIL populations derived from the cross of one common parent Yanzhan 1 (a Chinese domesticated cultivar) and four donor parents including Hussar (a British domesticated cultivar) and three semi-wild wheat varieties in China were phenotyped for 11 yield-related traits in eight environments. An integrated genetic map containing 2009 single-nucleotide polymorphism (SNP) markers generated from a 90 K SNP array was constructed to conduct quantitative trait loci (QTL) analysis. A total of 161 QTL were identified, including ten QTL for grain yield per plant (GYP) and yield components, 49 QTL for spike-related traits, 43 QTL for flag leaf-related traits, 22 QTL for plant height (PH), and 37 QTL for heading date and flowering date. Eight environmentally stable QTL were validated in individual RIL population where the target QTL was notably detected, and six of them had a significant effect on GYP. Furthermore, Two QTL, QSPS-2A.4 and QSL-4A.1, were also validated in a natural wheat population containing 580 diverse varieties or lines, which provided valuable resources for further fine mapping and genetic improvement in yield in wheat.

Dissecting genetic loci affecting grain morphological traits to improve grain weight via nested association mapping.

KEY MESSAGE: The quantitative trait loci (QTLs) for grain morphological traits were identified via nested association mapping and validated in a natural wheat population via haplotype analysis. Grain weight, one of the three most important components of crop yield, is largely determined by grain morphological traits. Dissecting the genetic bases of grain morphology could facilitate the improvement of grain weight and yield production. In this study, four wheat recombinant inbred line populations constructed by crossing the modern variety Yanzhan 1 with three semi-wild wheat varieties (i.e., Chayazheda, Yutiandaomai, and Yunnanxiaomai from Xinjiang, Tibet, and Yunnan, respectively) and one exotic accession Hussar from Great Britain were investigated for grain weight and eight morphological traits in seven environments. Eighty-eight QTLs for all measured traits were totally identified through nested association mapping utilizing 14,643 high-quality polymorphic single nucleotide polymorphism (SNP) markers generated by 90 K SNP array. Among them, 64 (72.7%) QTLs have the most favorable alleles donated by semi-wild wheat varieties. For 14 QTL clusters affecting at least two grain morphological traits, nine QTL clusters were located in similar position with known genes/QTL, and the other five were novel. Three important novel QTLs (i.e., qTGW-1B.1, qTGW-1B.2, and qTGW-1A.1) were further validated in a natural wheat population via haplotype analysis. The favorable haplotypes for these three QTLs might be used in marker-assisted selection for the improvement of wheat yield by modifying morphological traits.

Aegilops tauschii draft genome sequence reveals a gene repertoire for wheat adaptation.

About 8,000 years ago in the Fertile Crescent, a spontaneous hybridization of the wild diploid grass Aegilops tauschii (2n = 14; DD) with the cultivated tetraploid wheat Triticum turgidum (2n = 4x = 28; AABB) resulted in hexaploid wheat (T. aestivum; 2n = 6x = 42; AABBDD). Wheat has since become a primary staple crop worldwide as a result of its enhanced adaptability to a wide range of climates and improved grain quality for the production of baker's flour. Here we describe sequencing the Ae. tauschii genome and obtaining a roughly 90-fold depth of short reads from libraries with various insert sizes, to gain a better understanding of this genetically complex plant. The assembled scaffolds represented 83.4% of the genome, of which 65.9% comprised transposable elements. We generated comprehensive RNA-Seq data and used it to identify 43,150 protein-coding genes, of which 30,697 (71.1%) were uniquely anchored to chromosomes with an integrated high-density genetic map. Whole-genome analysis revealed gene family expansion in Ae. tauschii of agronomically relevant gene families that were associated with disease resistance, abiotic stress tolerance and grain quality. This draft genome sequence provides insight into the environmental adaptation of bread wheat and can aid in defining the large and complicated genomes of wheat species.

Construction of Agropyron Gaertn. genetic linkage maps using a wheat 660K SNP array reveals a homoeologous relationship with the wheat genome.

Agropyron Gaertn. (P genome) is a wild relative of wheat that harbours many genetic variations that could be used to increase the genetic diversity of wheat. To agronomically transfer important genes from the P genome to a wheat chromosome by induced homoeologous pairing and recombination, it is necessary to determine the chromosomal relationships between Agropyron and wheat. Here, we report using the wheat 660K single nucleotide polymorphism (SNP) array to genotype a segregating Agropyron F1 population derived from an interspecific cross between two cross-pollinated diploid collections 'Z1842' [A. cristatum (L.) Beauv.] (male parent) and 'Z2098' [A. mongolicum Keng] (female parent) and 35 wheat-A. cristatum addition/substitution lines. Genetic linkage maps were constructed using 913 SNP markers distributed among seven linkage groups spanning 839.7 cM. The average distance between adjacent markers was 1.8 cM. The maps identified the homoeologous relationship between the P genome and wheat and revealed that the P and wheat genomes are collinear and relatively conserved. In addition, obvious rearrangements and introgression spread were observed throughout the P genome compared with the wheat genome. Combined with genotyping data, the complete set of wheat-A. cristatum addition/substitution lines was characterized according to their homoeologous relationships. In this study, the homoeologous relationship between the P genome and wheat was identified using genetic linkage maps, and the detection mean for wheat-A. cristatum introgressions might significantly accelerate the introgression of genetic variation from Agropyron into wheat for exploitation in wheat improvement programmes.

The Wheat Mediator Subunit TaMED25 Interacts with the Transcription Factor TaEIL1 to Negatively Regulate Disease Resistance against Powdery Mildew.

Powdery mildew, caused by the biotrophic fungal pathogen Blumeria graminis f. sp. tritici, is a major limitation for the production of bread wheat (Triticum aestivum). However, to date, the transcriptional regulation of bread wheat defense against powdery mildew remains largely unknown. Here, we report the function and molecular mechanism of the bread wheat Mediator subunit 25 (TaMED25) in regulating the bread wheat immune response signaling pathway. Three homoalleles of TaMED25 from bread wheat were identified and mapped to chromosomes 5A, 5B, and 5D, respectively. We show that knockdown of TaMED25 by barley stripe mosaic virus-induced gene silencing reduced bread wheat susceptibility to the powdery mildew fungus during the compatible plant-pathogen interaction. Moreover, our results indicate that MED25 may play a conserved role in regulating bread wheat and barley (Hordeum vulgare) susceptibility to powdery mildew. Similarly, bread wheat ETHYLENE INSENSITIVE3-LIKE1 (TaEIL1), an ortholog of Arabidopsis (Arabidopsis thaliana) ETHYLENE INSENSITIVE3, negatively regulates bread wheat resistance against powdery mildew. Using various approaches, we demonstrate that the conserved activator-interacting domain of TaMED25 interacts physically with the separate amino- and carboxyl-terminal regions of TaEIL1, contributing to the transcriptional activation activity of TaEIL1. Furthermore, we show that TaMED25 and TaEIL1 synergistically activate ETHYLENE RESPONSE FACTOR1 (TaERF1) transcription to modulate bread wheat basal disease resistance to B. graminis f. sp. tritici by repressing the expression of pathogenesis-related genes and deterring the accumulation of reactive oxygen species. Collectively, we identify the TaMED25-TaEIL1-TaERF1 signaling module as a negative regulator of bread wheat resistance to powdery mildew.

The wheat transcription factor, TabHLH39, improves tolerance to multiple abiotic stressors in transgenic plants.

Although bHLH transcription factors play important roles regulating plant development and abiotic stress response and tolerance, few functional studies have been performed in wheat. In this study, we isolated and characterized a bHLH gene, TabHLH39, from wheat. The TabHLH39 gene is located on wheat chromosome 5DL, and the protein localized to the nucleus and activated transcription. TabHLH39 showed variable expression in roots, stems, leaves, glumes, pistils and stamens and was induced by polyethylene glycol, salt and cold treatments. Further analysis revealed that TabHLH39 overexpression in Arabidopsis significantly enhanced tolerance to drought, salt and freezing stress during the seedling stage, which was also demonstrated by enhanced abiotic stress-response gene expression and changes to several physiological indices. Therefore, TabHLH39 has potential in transgenic breeding applications to improve abiotic stress tolerance in crops.

The wheat MYB transcription factor TaMYB18 regulates leaf rolling in rice.

Leaf rolling is an important agronomic trait in crop breeding. Moderate leaf rolling maintains the erectness of leaves and minimizes shadowing between leaves, leading to improved photosynthetic efficiency. Although some genes controlling leaf rolling have been isolated from rice and other plant species, few studies have examined leaf rolling in wheat. In the present study, the leaf rolling regulator gene, TaMYB18, was identified in a large-scale transgene project involving the transformation of 1455 wheat transcription factor genes into rice. Three homologous sequences of TaMYB18 were isolated from hexaploid wheat and localized to chromosomes 5A, 5B and 5D, respectively. TaMYB18, an R2R3-MYB transcription factor, localized to the nucleus. TaMYB18 overexpression induced leaf rolling in transgenic rice. Additionally, the three members of TaMYB18 exhibited functional redundancy in rice. Furthermore, the function of TaMYB18 in regulating leaf rolling in rice was a dose-dependent. Taken together, these results indicate that TaMYB18 may play an important role in the regulation of leaf development.

The wheat MYB-related transcription factor TaMYB72 promotes flowering in rice.

Through large-scale transformation analyses, TaMYB72 was identified as a flowering time regulator in wheat. TaMYB72 is a MYB family transcription factor localized to the nucleus. Three TaMYB72 homologs, TaMYB72-A, TaMYB72-B and TaMYB72-D, cloned from hexaploid wheat were mapped to the short arm of the group 6 chromosomes. Under the long-day conditions, over-expression of the TaMYB72 in rice shortened the flowering time by approximately 12 d. Expression analyses suggest that TaMYB72 may function through up-regulation of florigen genes Hd3a and RFT1.

A novel wheat bZIP transcription factor, TabZIP60, confers multiple abiotic stress tolerances in transgenic Arabidopsis.

The basic region/leucine zipper (bZIP) transcription factors (TFs) play vital roles in the response to abiotic stress. However, little is known about the function of bZIP genes in wheat abiotic stress. In this study, we report the isolation and functional characterization of the TabZIP60 gene. Three homologous genome sequences of TabZIP60 were isolated from hexaploid wheat and mapped to the wheat homoeologous group 6. A subcellular localization analysis indicated that TabZIP60 is a nuclear-localized protein that activates transcription. Furthermore, TabZIP60 gene transcripts were strongly induced by polyethylene glycol, salt, cold and exogenous abscisic acid (ABA) treatments. Further analysis showed that the overexpression of TabZIP60 in Arabidopsis resulted in significantly improved tolerances to drought, salt, freezing stresses and increased plant sensitivity to ABA in seedling growth. Meanwhile, the TabZIP60 was capable of binding ABA-responsive cis-elements that are present in promoters of many known ABA-responsive genes. A subsequent analysis showed that the overexpression of TabZIP60 led to enhanced expression levels of some stress-responsive genes and changes in several physiological parameters. Taken together, these results suggest that TabZIP60 enhances multiple abiotic stresses through the ABA signaling pathway and that modifications of its expression may improve multiple stress tolerances in crop plants.

Characterization of a wheat R2R3-MYB transcription factor gene, TaMYB19, involved in enhanced abiotic stresses in Arabidopsis.

MYB-type proteins have been shown to participate in multiple stress responses. In the present study, we identified a gene in wheat induced by multiple abiotic stresses, TaMYB19, which encodes a R2R3-type MYB protein. Three highly homologous sequences of TaMYB19 were isolated from hexaploid wheat. Using the nulli-tetrasomic (NT) lines of Chinese Spring wheat, the three sequences were localized to chromosomes 1A, 1B and 1D and designated as TaMYB19-A, TaMYB19-B and TaMYB19-D, respectively. The expression patterns of these three genes were similar under different stress conditions. The TaMYB19-B sequence was selected for further analysis. The TaMYB19-B protein localized to the nucleus. A detailed characterization of Arabidopsis transgenic plants overexpressing the TaMYB19-B gene revealed that the TaMYB19-B protein could improve tolerance to multiple stresses during the seedling stage. We also found that the overexpression of TaMYB19-B resulted in changes in several physiological indices and altered the expression levels of a number of abiotic stress-related genes, allowing the plants to overcome adverse conditions. These results indicate that the TaMYB19 protein plays an important role in plant stress tolerance and that modification of the expression of this protein may improve abiotic stress tolerance in crop plants.