How do class II trehalose phosphate synthase proteins regulate wheat spike development?

The sugar signal trehalose 6-phosphate (T6P) is a strong indispensable regulator of plant metabolism, growth and development. We found that T6P inhibits the protein kinase, SnRK1 which can explain the strong effects of T6P through carbon and energy signalling. We are pursuing both genetics and chemistry to intervene in the T6P pathway for crop improvement. We published in Nature Biotechnology that increasing T6P levels in wheat grain with chemistry leads to sustainable increases in yield (per unit N and water) through T6P activation of > 100 genes for starch and protein synthesis in grain during early grain filling. This led to sink-led increases in photosynthesis (hence upregulation of whole source to sink pathway). Recalcitrant trade-offs between grain size and grain number and between grain size and grain protein are overcome by elevating T6P in grain. The T6P chemistry has emphasised the strong effect of T6P on metabolic regulation (whole primary pathways/ source-sink). Gene editing of class II TPSs is showing strong developmental regulation of TPSs which may have application in crop improvement too. Some TPS genes appear to be regulatory rather than catalytically active. In an association study in wheat some TPSs are linked to reproductive traits and some are still undergoing positive selection. We are using gene editing to better understand the function of these class II TPSs and how they might be modified for crop improvement. The T6P pathway affects the whole plant from top to bottom in a way perhaps unique for a plant regulatory system.