Identification of a type of von Willebrand factor

This study is reported by the group of Luxiang Liu from the Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing. Wheat production is essential for global food security, and continued improvement in grain yield is necessary to meet the nutritional needs of the expanding human population. Grain size is positively correlated with grain weight, while the flag leaf serves as the main source of photosynthetic assimilates for grain development, therefore grain and flag leaf morphologies are critical factors in the final yield potential of wheat. Identification of genes involved in grain and flag leaf morphologies remains an essential step in the precision breeding and cultivation of high-yield wheat. Chunyun Zhou, Hongchun Xiong and colleagues from Liu's group identified a von Willebrand factor type A (vWA)-/Vwaint domain-containing protein that affects grain size and flag leaf morphology by map-based cloning from a round grain 1 (rg1) wheat mutant, and they revealed the molecular mechanism of phenotypic variations in the mutants.

The team identified a round grain (rg1) mutant with shorter flag leaf and plant height from the background of winter wheat variety Zhongmai 175, and finely mapped the rg1 gene at a physical interval of 163 kb on chromosome 7D. Gene sequencing analysis indicated that the TraesCS7D02G010200 encoding a protein containing a vWA domain and Vwaint was the candidate gene for RG1. Missense mutations in seven round-grained/short-leafed mutants from the backgrounds of Jing411 and Nongda5181 confirmed that TraesCS7D02G010200 was the gene responsible for the altered grain size and flag leaf morphology. Additional protein structural modeling indicated that amino acid substitutions located at sites critical for protein folding, particularly in the highly conserved Vwaint domain, resulted in the round grain/short flag leaf phenotype. Further protein interaction and hormone content analyses suggest that RG1 may regulate GA and ABA levels via interaction with the isoprenoid synthesis protein, MCT, which may contribute to the reduced grain size and flag leaf length. In addition, natural variation populations were also used to identify haplotypes associated with variable grain size-related traits.

This study reveals the functions of the vWA domain in regulating grain size and flag leaf morphology. It provides a theoretical basis and genetic resources, including RG1 haplotypes, that may facilitate the improvement of grain size and weight in wheat and potentially other cereal crops.