A single CHI gene suffices to increase flavonol content in tomato peel (Colliver and others 2002). Although the chalcone synthase (CHS), CHI, flavanone-3-hydroxylase (F3H), and flavonol synthase (FLS) genes were ectopically expressed simultaneously, the flavonol content of the tomato with the 4 genes was not significantly increased compared with tomatoes in which only the CHI gene was expressed.