Temporal and Spatial Expression of Genes Involved in Anthocyanin Biosynthesis during Sweet Potato (Ipomoea batatas [L.] Lam.) Root Development

To elucidate the gene regulation of pigmentation in sweet potato, expressions of the genes involved in anthocyanin biosynthesis were investigated in correlation with the accumulation of the anthocyanins during plant development. Fragments of the anthocyanin biosynthetic pathway genes involved in the central flavonoid pathway, including those for chalcone synthase (CHS), chalcone isomerase (CHI), flavone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and UDPG-flavonoid-3-0-glucosyltransferase (UF3GT) were investigated in sweet potato, and their expressions were characterized in various tissues and developmental stages in both purple- and yellow-fleshed varieties. Transcription patterns of the anthocyanin biosynthetic genes show accumulation at the early stages of root development (10–30 d after planting), followed by a decline. The anthocyanin biosynthetic genes were expressed throughout all stages of root development, wherein their expressions were activated at the stages corresponding to anthocyanin accumulation. Quantification of total anthocyanin content in various sweet potato tissues showed that the anthocyanin content of the purple-fleshed variety was highly concentrated in all root types except in the lateral roots, while in the yellowfleshed variety, anthocyanin content was highest in the pigmented roots. The anthocyanin content at the different developmental stages of the sweet potato plant is highest during the early stages of development (10–30 d after planting), which is in accordance with the transcription levels of the anthocyanin biosynthetic genes.