Recently, bread wheat production is exposed to threat due to drought disaster all over the world. In addition, fresh water availability for agriculture is predicted to decline by a half in 2050 compared with at present, owing to global climate change. In contrast, world population keeps increasing and is predicted to reach 9.7-10 billion in 2050. To ensure food security of ours and increase yield, we should create environmentally robust wheat cultivar. To enhance wheat robustness against drought, understanding the drought tolerant mechanism is one of the important points. Seed shrinkage caused by inhibition of endosperm development due to drought stress is a negative effect to reduce wheat yield. However, little is known on the molecular mechanism.

Then, we investigated how drought stress on seed developmental stage affects seed quality related traits such as seed storage protein (SSP) and starch, using drought tolerant wheat by overexpressing an abscisic acid receptor gene (TaPYLox) developed in previous study. Consequently, TaPYLox was little damaged, but the control was damaged in both SSPs and starch granules due to drought stress. Gene ontology (GO) analysis based on transcriptome showed that the genes belonging to GOs including translation and protein biosynthesis were downregulated in the control under severe drought condition. This suggests that SSP biosynthesis could be inhibited by decreased translational process and protein biosynthesis. Furthermore, metabolite analysis indicated a variety of amino acids shortage in the control under severe drought condition. This also suggests that transportation of these amino acids into endosperm could not be inhibited, eventually ingredients of SSPs exhausted. Our study proposed that decreased SSPs due to drought stress would be caused by insufficient amino acids and malfunctional protein biosynthesis process.