Adaptive Significance and Origin of Flavonoid Biosynthesis Genes in the Grain of Cultivated Cereals

The majority of cultivated cereals including maize, rice, wheat, barley, oat and rye consist of numerous varieties lacking anthocyanin pigmentation or having weak coloration of vegetative organs and/or caryopses. Only rare local races and wild related species have intense coloration of plants and/or grains. The coloration of caryopses is associated with the biosynthesis of colored flavonoids in maternal (pericarp and testa) and hybrid (aleurone) caryopsis tissues. The trait is controlled by dominant alleles of regulatory genes encoding conserved transcription factors of the MYB, bHLH-MYC, and WD40 families forming the MBW protein complex. Recent studies have proven the participation of uncolored and colored flavonoids in the response of plants to biotic and abiotic stresses, and the significance of their presence in the whole grain foods has been determined. However, many questions about the adaptive effects and health benefits of anthocyanins remain unanswered. In particular, the reasons why the dominant alleles of regulatory genes controlling pericarp coloration did not become widespread in the course of domestication and breeding of cereals are not clear, although these genes receive special attention in association with health-improving effects of grain nutrition. This article discusses the similarity and specificity of the genetic control of the biosynthesis of flavonoids in the caryopsis in three related cultivated cereals, wheat, barley, and rye, and their biological role in the development of the caryopsis and seed germination.