Molecular Mechanisms of Carnation Flower Colors via Anthocyanin and Flavonoid Biosynthetic Pathways

Anthocyanin synthesis is initiated by the phenylpropanoid pathway followed by aglycone synthesis; the products of synthesis are then modified with glucose and malate. Genes for the enzymes in the phenylpropanoid pathway consist of small gene families in Carnation database (DB) and particular gene(s) are expressed during anthocyanin and flavonol syntheses in petals. After phenylpropanoid metabolism, the enzymes chalcone synthase, chalcone isomerase, and flavanone 3-hydroxylase, which are categorized as early biosynthetic genes and consist of small gene families, supply intermediates for both anthocyanin and flavonol syntheses. The intermediates are catabolized by dihydroflavonol 4-reductase followed by anthocyanidin synthase; some intermediates are hydroxylated by flavonol 3′-hydroxylase; these three enzymes are encoded by genes categorized as late biosynthetic genes and consist of single genes in Carnation DB. Anthocyanidin is glucosylated by cytosolic UDP-glucose-dependent glucosyltransferase, a member of glycosyltransferase family 1, at the 3 position followed by transportation into vacuoles (or endoplasmic reticulum). Anthocyanin 3-O-glucoside is malylated by serine carboxypeptidase-like (SCPL) malyltransferase followed by glucosylation at the 5 position by a glycoside hydrolase family 1 (GH1) enzyme; both use acyl-glucose as a donor. Genes for these enzymes probably evolved from ancestral SCPL and GH1 genes by local gene duplication associated with neofunctionalization and subfunctionalization.