Identification and expression analysis of genes involved in anthocyanin and proanthocyanidin biosynthesis in the fruit of blackberry

Anthocyanin and proanthocyanin are two major secondary metabolites involved in fruit maturation. In this work, the variations of anthocyanin and proanthocyanidin content were determined during blackberry fruit development. Genes associated with biosynthesis of both two compounds were isolated. Expression patterns of these genes were also investigated by quantitative PCR throughout fruit maturation. Anthocyanins, which remained at a low concentration in the early developing stage, increased dramatically as the fruit matured. On the contrary, proanthocyanidins exhibited a continuously decreasing pattern. Transcript levels of genes specifically controlling either of these two compounds: anthocyanin synthase (RuANS) for anthocyanin, leucoanthocyanidin reductase (RuLAR) and anthocyanidin reductase (RuANR) for proanthocyanidin, were generally coordinated with the products' changing patterns. The expression of the RuMYB10, encoding a transcription factor, was also concomitant with the synthesis of anthocyanins, indicating its specificity regulation role in anthocyanin branch. The other two genes, chalcone synthase (RuCHS) and dihydroflavonol 4-reductase (RuDFR), showed cross regulation for not only the synthesis of anthocyanin and proanthocyanidin, but also other flavonoid compounds. According to the temporal expression patterns, the isolated RuGT gene might encode a glucosyltransferase participating in modifying metabolites besides anthocyanins. Our discoveries of the temporal gene expression and compounds accumulation will shed new light into genetic and physiological metabolisms in blackberry fruit development, thus assisting in future attempts to alter anthocyanin or PA metabolites in fruits. (C) 2012 Elsevier B.V. All rights reserved.