TaNAM-6A is essential for nitrogen remobilisation and regulates grain protein content in wheat (Triticum aestivum L.).

Grain protein content (GPC) is a crucial quality trait in bread wheat, which is influenced by the key transcription factor TaNAM. However, the regulatory mechanisms of TaNAM have remained largely elusive. In this study, a new role of TaNAM was unveiled in regulating nitrogen remobilisation which impacts GPC. The TaNAM knockout mutants generated by clustered regularly interspaced short palindromic repeats/Cas9 exhibited significantly delayed senescence and lower GPC, while overexpression of TaNAM-6A resulted in premature senility and much higher GPC. Further analysis revealed that TaNAM directly activates the genes TaNRT1.1 and TaNPF5.5s, which are involved in nitrogen remobilisation. This activity aids in the transfer of nitrogen from leaves to grains for protein synthesis. In addition, an elite allele of TaNAM-6A, associated with high GPC, was identified as a candidate gene for breeding high-quality wheat. Overall, our work not only elucidates the potential mechanism of TaNAM-6A affecting bread wheat GPC, but also highlights the significance of nitrogen remobilisation from senescent leaves to grains for protein accumulation. Moreover, our research provides a new target and approach for improving the quality traits of wheat, particularly the GPC.

Heat Stress Tolerance 2 confers basal heat stress tolerance in allohexaploid wheat (Triticum aestivum L.).

Heat stress substantially reduces the yield potential of wheat (Triticum aestivum L.), one of the most widely cultivated staple crops, and greatly threatens global food security in the context of global warming. However, few studies have explored the heat stress tolerance (HST)-related genetic resources in wheat. Here, we identified and fine-mapped a wheat HST locus, TaHST2, which is indispensable for HST in both the vegetative and reproductive stages of the wheat life cycle. The studied pair of near isogenic lines (NILs) exhibited diverse morphologies under heat stress, based on which we mapped TaHST2 to a 485 kb interval on chromosome arm 4DS. Under heat stress, TaHST2 confers a superior conversion rate from soluble sugars to starch in wheat grains, resulting in faster grain filling and a higher yield potential. A further exploration of genetic resources indicated that TaHST2 underwent strong artificial selection during wheat domestication, suggesting it is an essential locus for basal HST in wheat. Our findings provide deeper insights into the genetic basis of wheat HST and might be useful for global efforts to breed heat-stress-tolerant cultivars.

Genome-wide association study of six quality-related traits in common wheat (Triticum aestivum L.) under two sowing conditions.

KEY MESSAGE: We identified genomic regions associated with six quality-related traits in wheat under two sowing conditions and analyzed the effects of multienvironment-significant SNPs on the stability of these traits. Grain quality affects the nutritional and commercial value of wheat (Triticum aestivum L.) and is a critical factor influencing consumer preferences for specific wheat varieties. Climate change is predicted to increase environmental stress and thereby reduce wheat quality. Here, we performed a genotyping assay involving the use of the wheat 90 K array in a genome-wide association study of six quality-related traits in 486 wheat accessions under two sowing conditions (normal and late sowing) over 4 years. We identified 64 stable quantitative trait loci (QTL), including 10 for grain protein content, 9 for wet gluten content, 4 for grain starch content, 14 for water absorption, 15 for dough stability time and 12 for grain hardness in wheat under two sowing conditions. These QTL harbored 175 single nucleotide polymorphisms (SNPs), explaining approximately 3-13% of the phenotypic variation in multiple environments. Some QTL on chromosomes 6A and 5D were associated with multiple traits simultaneously, and two (QNGPC.cau-6A, QNGH.cau-5D) harbored known genes, such as NAM-A1 for grain protein content and Pinb for grain hardness, whereas other QTL could facilitate gene discovery. Forty-three SNPs that were detected under late or both normal and late sowing conditions appear to be related to phenotypic stability. The effects of these SNP alleles were confirmed in the association population. The results of this study will be useful for further dissecting the genetic basis of quality-related traits in wheat and developing new wheat cultivars with desirable alleles to improve the stability of grain quality.

Over-Expressing TaSPA-B Reduces Prolamin and Starch Accumulation in Wheat (Triticum aestivum L.) Grains.

Starch and prolamin composition and content are important indexes for determining the processing and nutritional quality of wheat (Triticum aestivum L.) grains. Several transcription factors (TFs) regulate gene expression during starch and protein biosynthesis in wheat. Storage protein activator (TaSPA), a member of the basic leucine zipper (bZIP) family, has been reported to activate glutenin genes and is correlated to starch synthesis related genes. In this study, we generated TaSPA-B overexpressing (OE) transgenic wheat lines. Compared with wild-type (WT) plants, the starch content was slightly reduced and starch granules exhibited a more polarized distribution in the TaSPA-B OE lines. Moreover, glutenin and ω- gliadin contents were significantly reduced, with lower expression levels of related genes (e.g., By15, Dx2, and ω-1,2 gliadin gene). RNA-seq analysis identified 2023 differentially expressed genes (DEGs). The low expression of some DEGs (e.g., SUSase, ADPase, Pho1, Waxy, SBE, SSI, and SS II a) might explain the reduction of starch contents. Some TFs involved in glutenin and starch synthesis might be regulated by TaSPA-B, for example, TaPBF was reduced in TaSPA-B OE-3 lines. In addition, dual-luciferase reporter assay indicated that both TaSPA-B and TaPBF could transactivate the promoter of ω-1,2 gliadin gene. These results suggest that TaSPA-B regulates a complex gene network and plays an important role in starch and protein biosynthesis in wheat.

Genome-Wide Association Study Reveals the Genetic Basis of Five Quality Traits in Chinese Wheat.

Bread wheat is a highly adaptable food crop grown extensively around the world and its quality genetic improvement has received wide attention. In this study, the genetic loci associated with five quality traits including protein content (PC), gluten content (GC), baking value (BV), grain hardness (HA), and sedimentation value (SV) in a population of 253 Chinese wheat grown in Inner Mongolia were investigated through genome wide association mapping. A total of 103 QTL containing 556 SNPs were significantly related to the five quality traits based on the phenotypic data collected from three environments and BLUP data. Of these QTL, 32 QTL were continuously detected under at least two experiments. Some QTL such as qBV3D.2/qHA3D.2 on 3D, qPC5A.3/qGC5A on 5A, qBV5D/qHA5D on 5D, qBV6B.2/qHA6B.3 on 6B, and qBV6D/qHA6D.1 on 6D were associated with multiple traits. In addition, distribution of favorable alleles of the stable QTL in the association panel and their effects on five quality traits were validated. Analysis of existing transcriptome data revealed that 34 genes were specifically highly expressed in grains during reproductive growth stages. The functions of these genes will be characterized in future experiments. This study provides novel insights into the genetic basis of quality traits in wheat.

Differential effects of a post-anthesis heat stress on wheat (Triticum aestivum L.) grain proteome determined by iTRAQ.

Heat stress, a major abiotic stressor of wheat (Triticum aestivum L.), often results in reduced yield and decreased quality. In this study, a proteomic method, Tags for Relative and Absolute Quantitation Isobaric (iTRAQ), was adopted to analyze the protein expression profile changes among wheat cultivar Jing411 under heat stress. Results indicated that there were 256 different proteins expressed in Jing411 under heat stress. According to the result of gene annotation and functional classification, 239 proteins were annotated by 856 GO function entries, including growth and metabolism proteins, energy metabolism proteins, processing and storage proteins, defense-related proteins, signal transduction, unknown function proteins and hypothetical proteins. GO enrichment analysis suggested that the differentially expressed proteins in Jing411 under heat stress were mainly involved in stimulus response (67), abiotic stress response (26) and stress response (58), kinase activity (12), and transferase activity (12). Among the differentially expressed proteins in Jing411, 115 were attributed to 119 KEGG signaling/metabolic pathways. KEGG pathway enrichment analysis in Jing411 showed that heat stress mainly affected the starch and sucrose metabolism as well as protein synthesis pathway in the endoplasmic reticulum. The protein interaction network indicated that there were 8 differentially expressed proteins that could form an interaction network in Jing411.