Fig. 1.

Simplified flavonoid biosynthesis pathway. The enzymes in the pathway are: CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; DFR, dihydroflavonol 4-reductase; ANS, anthocyanidin synthase; 3GT, UDP-glucose:flavonoid 3-O-glucosyltransferase; FNS, flavone synthase; FLS, flavonol synthase. The arrowheads indicate modification steps of anthocyanins, which are mediated by glycosyltransferases, acyltransferases, and methyltransferases. Hypothesis 1 of EFP function: EFP enhances CHS activity. Hypothesis 2 of EFP function: EFP interacts with biosynthesis enzymes and forms a metabolon complex.