Two Tightly Linked Genes Controlling Grain Length Underlie a Major Grain Weight QTL in Polyploid Wheat

Wheat provides ~20% of the calories and ~25% of protein consumed by humans. However, a step-change in yield increase must be delivered to keep up with current and future demand. Final grain yield is a highly complex trait influenced by many genetic and environmental factors and as such is not well understood. Grain weight, determined by grain length and width, is an important yield component: we hypothesise that identifying the genes controlling grain weight will provide a targeted route to manipulating yield in wheat.

We have identified a stable quantitative trait loci (QTL) on chromosome 5A for thousand grain weight (TGW) and validated it using BC₄-Near Isogenic Lines (NILs) across several years and environments. The effect on TGW is specifically driven by an increase in grain length. Fine mapping of the QTL suggests that there are two tightly linked genes, GL-A1 and GL-A2, which are linked in cis and have an additive effect on grain length. Characterisation of the GL-A1 and GL-A2 NILs suggests that these genes affect early grain development and act to increase the length, but not the number, of pericarp cells. Transcriptomic analysis has identified genes from distinct biological pathways which are differentially expressed. These genes, together with candidate genes within the physical space determined from the newly available wheat genome, are being investigated using mutants identified from the wheat exome-captured TILLING platform. Pyramiding of GL-A1 and GL-A2 with the grain weight GW2 gene leads to additive effects on TGW.