The TaSnRK1-TabHLH489 module integrates brassinosteroid and sugar signalling to regulate the grain length in bread wheat.

Regulation of grain size is a crucial strategy for improving the crop yield and is also a fundamental aspect of developmental biology. However, the underlying molecular mechanisms governing grain development in wheat remain largely unknown. In this study, we identified a wheat atypical basic helix-loop-helix (bHLH) transcription factor, TabHLH489, which is tightly associated with grain length through genome-wide association study and map-based cloning. Knockout of TabHLH489 and its homologous genes resulted in increased grain length and weight, whereas the overexpression led to decreased grain length and weight. TaSnRK1α1, the α-catalytic subunit of plant energy sensor SnRK1, interacted with and phosphorylated TabHLH489 to induce its degradation, thereby promoting wheat grain development. Sugar treatment induced TaSnRK1α1 protein accumulation while reducing TabHLH489 protein levels. Moreover, brassinosteroid (BR) promotes grain development by decreasing TabHLH489 expression through the transcription factor BRASSINAZOLE RESISTANT1 (BZR1). Importantly, natural variations in the promoter region of TabHLH489 affect the TaBZR1 binding ability, thereby influencing TabHLH489 expression. Taken together, our findings reveal that the TaSnRK1α1-TabHLH489 regulatory module integrates BR and sugar signalling to regulate grain length, presenting potential targets for enhancing grain size in wheat.

Identifying cis-Acting Elements Associated with the High Activity and Endosperm Specificity of the Promoters of Genes Encoding Low-Molecular-Weight Glutenin Subunits in Common Wheat (Triticum aestivum).

Low-molecular-weight glutenin subunits (LMW-GSs) associated with bread-baking quality and flour nutrient quality accumulate in endosperms of common wheat and related species. However, the mechanism underlying the expression regulation of genes encoding LMW-GSs has not been fully elucidated. In this study, we identified LMW-D2 and LMW-D7, which are highly and weakly expressed, respectively, via the analysis of RNA-sequencing data of Chinese Spring wheat and wheat transgenic lines transformed with 5' deletion promoter fragments and GUS fusion constructs. The 605-bp fragment upstream of the LMW-D2 start codon could drive high levels of GUS expression in the endosperm. The truncated endosperm box located at the -300 site resulted in the loss of LMW-D2 promoter activity, and a single-nucleotide polymorphism on the GCN4 motif was closely related to the expression of LMW-GSs. TCT and TGACG motifs, as well as the others located on the 5' distal end, might also be involved in the transcription regulation of LMW-GSs. In transgenic lines, fusion proteins of LMW-GS and GUS were deposited into protein bodies. Our findings provide new insights into the mechanism underlying the transcription regulation of LMW-GSs and will contribute to the development of wheat endosperm as a bioreactor for the production of nutraceuticals, antibodies, vaccines, and medicinal proteins.

Fine Mapping of the Wheat Leaf Rust Resistance Gene LrLC10 (Lr13) and Validation of Its Co-segregation Markers.

Wheat leaf rust, caused by the fungus Puccinia triticina Eriks. (Pt), is a destructive disease found throughout common wheat production areas worldwide. At its adult stage, wheat cultivar Liaochun10 is resistant to leaf rust and the gene for that resistance has been mapped on chromosome 2BS. It was designated LrLC10 and is the same gene as cataloged gene Lr13 by pedigree analysis and allelism test. We fine-mapped it using recessive class analysis (RCA) of the homozygous susceptible F2 plants derived from crosses using Liaochun10 as the resistant, male parent. Taking advantage of the re-sequencing data of Liaochun10 and its counterpart susceptible parent, we converted nucleotide polymorphisms in the LrLC10 interval between the resistant and susceptible parents into molecular markers to saturate the LrLC10 genetic linkage map. Four indel markers were added in the 1.65 cM map of LrLC10 flanked by markers CAUT163 and Lseq22. Thirty-two recombinants were identified by those two markers from the 984 F2 homozygous susceptible plants and were further genotyped with additional ten markers. LrLC10 was finally placed in a 314.3 kb region on the Chinese Spring reference sequence (RefSeq v1.0) that contains three high confidence genes: TraesCS2B01G182800, TraesCS2B01G182900, and TraesCS2B01G183000. Sequence analysis showed several variations in TraesCS2B01G182800 and TraesCS2B01G183000 between resistant and susceptible parents. One KASP marker and an indel marker were designed based on the differences in those two genes, respectively, and were validated to be diagnostic co-segregating markers for LrLC10. Our results both improve marker-assisted selection and help with the map-based cloning of LrLC10.

Interaction between serine carboxypeptidase-like protein TtGS5 and Annexin D1 in developing seeds of Triticum timopheevi.

GS5 encoding a serine carboxypeptidase-like protein positively regulates grain size and weight through the regulation of grain width and filling and is helpful in improving cereal yields. Grain width variation determined by GS5 is associated with cell number and size, but the actual underlying mechanism is still unclear. Two orthologs of GS5, TtGS5-3A-G and TtGS5-3G-G, were cloned from the Triticum timopheevi accession no. CWI17006. To identify the proteins that interacted with TtGS5-3A-G and TtGS5-3G-G in premature grains, we performed pull-down assays followed by liquid chromatography-mass spectrometry/mass spectrometry analysis. The analyses revealed 18 proteins were present in both the TtGS5-3A-G and TtGS5-3G-G interactomes. Among five candidates selected, only Annexin D1 interacted with both TtGS5-3A-G and TtGS5-3G-G in yeast. Annexin D1, TtGS5-3A-G, and TtGS5-3G-G were located on the cytoplasmic membranes of Arabidopsis protoplasts and onion epidermal cells, and interactions between Annexin D1 and TtGS5-3A-G, as well as TtGS5-3G-G, were shown by bimolecular fluorescence complementation assays. Annexin D1 was expressed widely in different tissues, and it co-expressed with TtGS5-3A-G/TtGS5-3G-G at the grain enlargement phase. These results indicated that Annexin D1 interacted with TtGS5-3A-G and TtGS5-3G-G in premature grains. Together with the structural similarities of Annexin D1 to known fiber elongation factors, we proposed that TtGS5 might regulate the cell size by interacting with Annexin D1. The results provide significant new information for understanding the roles that GS5 plays in regulating grain size, which may be useful in improving crop yields.

Analyzing the action of evolutionarily conserved modules on HMW-GS 1Ax1 promoter activity.

KEY MESSAGE: The specific and high-level expression of 1Ax1 is determined by different promoter regions. HMW-GS synthesis occurs in aleurone layer cells. Heterologous proteins can be stored in protein bodies. High-molecular-weight glutenin subunit (HMW-GS) is highly expressed in the endosperm of wheat and relative species, where their expression level and allelic variation affect the bread-making quality and nutrient quality of flour. However, the mechanism regulating HMW-GS expression remains elusive. In this study, we analyzed the distribution of cis-acting elements in the 2659-bp promoter region of the HMW-GS gene 1Ax1, which can be divided into five element-enriched regions. Fragments derived from progressive 5' deletions were used to drive GUS gene expression in transgenic wheat, which was confirmed in aleurone layer cells, inner starchy endosperm cells, starchy endosperm transfer cells, and aleurone transfer cells by histochemical staining. The promoter region ranging from - 297 to - 1 was responsible for tissue-specific expression, while fragments from - 1724 to - 618 and from - 618 to - 297 were responsible for high-level expression. Under the control of the 1Ax1 promoter, heterologous protein could be stored in the form of protein bodies in inner starchy endosperm cells, even without a special location signal. Our findings not only deepen our understanding of glutenin expression regulation, trafficking, and accumulation but also provide a strategy for the utilization of wheat endosperm as a bioreactor for the production of nutrients and metabolic products.

Genome-wide identification of internal reference genes for normalization of gene expression values during endosperm development in wheat.

Internal reference genes that are stably expressed are essential for normalization in comparative expression analyses. However, gene expression varies significantly among species, organisms, tissues, developmental stages, stresses, and treatments. Therefore, identification of stably expressed reference genes in developmental endosperm of bread wheat is important for expression analysis of endosperm genes. As the first study to systematically screen for reference genes across different developmental stages of wheat endosperm, nine genes were selected from among 76 relatively stable genes based on high-throughput RNA sequencing data. The expression stability of these candidate genes and five traditional reference genes was assessed by real-time quantitative PCR combined with three independent algorithms: geNorm, NormFinder, and BestKeeper. The results showed that ATG8d was the most stable gene during wheat endosperm development, followed by Ta54227, while the housekeeping gene GAPDH, commonly used as an internal reference, was the least stable. ATG8d and Ta54227 together formed the optimal combination of reference genes. Comparative expression analysis of glutenin genes indicated that credible quantification could be achieved by normalization against ATG8d in developmental endosperm. The stably expressed gene characterized here can act as a proper internal reference for expression analysis of wheat endosperm genes, especially nutrient- and nutrient synthesis-related genes.

Effects of high-molecular-weight glutenin subunit combination in common wheat on the quality of crumb structure.

BACKGROUND: High-molecular-weight glutenin subunits (HMW-GSs) have important effects on bread-making quality. Allelic variations of HMW-GS in bread wheat varieties contribute in different ways to dough properties and bread volume. However, no systematic analysis has been done on the effects of allelic variation on bread-crumb structure, an important parameter when evaluating bread-making quality. In this study, seven Glu-1 deletion lines and one intact line harboring different encoding loci and derived from a cross between two spring wheat cultivars were used to investigate the contribution of a single Glu-1 locus, or combination of Glu-1 loci, to the crumb structure. RESULTS: Deletion of HMW-GS locus combinations resulted in a decline in slice size, brightness, and fineness of the bread crumb. A desirable crumb structure correlated well with preferred subunit combinations: high levels of GMPs, superior dough properties, and loaf volume. The effects of the HMW-GS combinations were ranked as Dx5 + Dy10 > Bx17 + By18 > Ax1 + Null. The Ax1 + Null allele affected the crumb structure by interacting with the Bx17 + By18 or Dx5 + Dy10. CONCLUSION: High-molecular-weight glutenin subunits had significant effects on the loaf volume and crumb structure; varying effects from different subunit combinations were observed. © 2018 Society of Chemical Industry.