Expression and mapping of anthocyanin biosynthesis genes in carrot

Anthocyanin gene expression has been extensively studied in leaves, fruits and flowers of numerous plants. Little, however, is known about anthocyanin accumulation in roots, or in carrots or other Apiaceae. We quantified expression of six anthocyanin biosynthetic genes (phenylalanine ammonia-lyase (PAL3), chalcone synthase (CHS1), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR1), leucoanthocyanidin dioxygenase (LDOX2), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT)) in three carrot inbreds with contrasting root color: solid purple (phloem and xylem); purple outer phloem/orange xylem; and orange phloem and xylem. Transcripts for five of these genes (PAL3, CHS1, F3H, DFR1, LDOX2) accumulated at high levels in solid purple carrots, less in purple orange carrot, and low or no transcript in orange carrots. Gene expression coincided with anthocyanin accumulation. In contrast, UFGT expression was comparable in purple and orange carrots, and relatively unchanged during root development. We genetically mapped five of the anthocyanin biosynthesis genes (FLS1 (flavonol synthase), DFR1, F3H, LDOX2, and PAL3) and two anthocyanin transcription factors (DcMYB3 and DcMYB5) in a population segregating for the P1 locus that conditions purple storage root color. The F3H and FLS1 genes were < 1 cM apart on chromosome 3, and < 3 cM from P1, while LDOX2 and PAL3 were unlinked to P1. The gene expression and mapping data suggests a coordinated regulatory control of anthocyanin expression in carrot root and establish a framework for studying the anthocyanin pathway in carrots, and they also suggest that none of the genes evaluated is a candidate for P1.