Transcriptional regulatory mechanisms of flavonoid metabolism from flower bud to flower in Hemerocallis citrina

The flower buds of Hemerocallis citrina are well-known functional foods in East Asian countries for their promoting intelligence and forgetting worries, in which their nutrients, especially flavonoids, play an important role. However, they will be discarded when the buds develop into flowers, part of the reason is the type and content of flavonoids change considerably. At present, the developmental mechanism responsible for these differences is still unclear. Based on "multi-omics" technologies, the results of this study revealed that 18 flavonoids were significantly differential, including five flavonoids, eight flavonols and three flavanones, one isoflavone and one anthocyanin, and their biosynthesis involved 50 differential genes and 25 differential enzyme proteins. Among them, nine genes encoding four key enzymes (chalcone isomerase, isoflavone 2′-hydroxylase, flavonol-3-O-l-rhamnoside-7-O-glucosyltransferase and phlorizin synthase) were targeted by seven conserved miRNA (microRNA) families, covering miR394, miR477, miR396, miR528, miR164, miR395 and miR447. Furthermore, 10 genes encoding five transcription factor families (bZIP (basic leucine zipper), NAC (NAM, ATAF1/2 and CUC2), GRAS (GAI, RGA and SCR), TCP (TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR) and MADS (MCM1/AGAMOUS/DEFICIENS/SRF)) were targeted by seven conserved miRNA families, including miR393, miR166, miR171, miR477, miR164, miR528 and miR447. They are jointly involved in the metabolic regulation of flavone and flavonol biosynthesis, isoflavonoid biosynthesis, and flavonoid biosynthesis from flower buds to flowering development of H. citrina.