Selection of dysfunctional alleles of bHLH1 and MYB1 genes produces white grain in the tribe Triticeae

Grain color is a key agronomic trait that greatly determines food quality. Elucidating the molecular and evolutionary mechanism underlying grain color regulation is also an important question in evolutionary biology and crop breeding. Here, we confirm that both bHLH and MYB play a critical role in controlling grain color evolution in Triticeae. Blue grain is the ancestral trait, while white grain caused by dysfunctions of bHLH or MYB is the derived trait in Triticeae. HvbHLH1 and HvMYB1 are the targets of selection in barley, and dysfunctionalized by deletion(s), insertion(s) and point mutation(s) in vast majority of Triticeae species accompanied by the alteration from blue grain to white grain. Wheat with white grain exhibits high seed vigor under stresses. Artificial co-expressions of ThbHLH1 and ThMYB1 in grain endosperm and aleurone layer generates color grains with health benefits and is used in a new hybrid breeding technology in wheat, respectively. Therefore, our study reveals that white grain might be a favorable derived trait and kept through natural/artificial selection in Triticeae, and ancient blue grain could be regained and reused in the modern technology of molecular breeding in modern wheat.