Flavonoids in major cereal grasses: distribution, functions, biosynthesis, and applications

Abstract

<p>Cereal food crops like maize (<em>Zea mays</em>), rice (<em>Oryza sativa</em>), sorghum (<em>Sorghum bicolor</em>) and wheat (<em>Triticum aestivum</em>) are members of the grass family (Poaceae). Together with bioenergy grasses, they play essential roles in agriculture and biorefinery, comprising an important component of bio-economy. Grasses accumulate a unique range of flavonoids (a class of plant-specific specialized metabolites) that contribute to defense responses, fertility, pigmentation and cell wall lignification. This review summarizes the distribution, functions, biosynthesis and regulation of flavonoids, including flavanones, tricin and flavone <em>O</em>-conjugates, flavone <em>C</em>-glycosides, 3-deoxyanthocyanidins, phlobaphenes, anthocyanins, proanthocyanidins (condensed tannins) and flavonols, in grasses focusing on model cereal grasses. In particular, the constitutive, predominant and widespread tricin-lignin, flavone <em>O</em>-conjugates and flavone <em>C</em>-glycosides as well as the inducible and/or lineage-specific sakuranetin (a flavanone), maysin (a flavone <em>C</em>-glycoside), 3-deoxyanthocyanidins and phlobaphenes, are highlighted. Finally, the impacts and importance of cereal grass flavonoids on scientific research, agricultural production, food and health, and biorefinery are discussed.</p>