Identification of the Biosynthetic Pathway for Anthocyanin Triglucoside, the Precursor of Polyacylated Anthocyanin, in Red Cabbage

Red cabbage anthocyanin is utilized as a natural food colorant because of its stable and brilliant coloration. The major anthocyanin of red cabbage is cyanidin (Cy) mono- and di-acyltriglucoside; however, the biosynthetic pathway to generate this anthocyanin remains unclear. We isolated and identified four uridine diphosphate-glucose-dependent glucosyltransferase (UGT) cDNAs from red cabbage using RNA-seq. UGTs are involved in Cy triglucoside (CytriG) synthesis, the precursor of Cy acyltriglucoside. Enzymatic assays using recombinant proteins suggested that UGT78D5 encodes Cy 3GT, UGT79B45 encodes Cy 3-glucoside GT, UGT75C2 encodes Cy 3-sophoroside (Cy3Sp) 5GT, and UGT79B44 encodes flavonol 3-glucoside GT. Anthocyanin GT assays using crude proteins prepared from red cabbage suggested that CytriG is produced from intermediate products in the following order: Cy, Cy3G, Cy3Sp, and CytriG.