Deciphering the Molecular Mechanisms Controlling Grain Length in 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 is an important yield component: we hypothesise that identifying the genes controlling grain weight will provide a targeted route to manipulating yield in wheat. Grain weight is determined by grain length, grain width and grain filling characteristics.

We have identified a stable quantitative trait loci 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 underlying 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 of cells in the grain. Transcriptomic analysis has identified genes from specific biological pathways which are differentially expressed. Candidate genes are now being investigated using mutants identified from the newly developed exome-captured TILLING platform. We are also conducting haplotype analysis using exome capture data from a wide range of germplasm to understand the allelic variation across candidates across the GL-A1 and GL-A2 regions.