Comparative Transcriptomic Analysis Reveals Flavonoid Biosynthesis Regulation in Chinese Bayberry (Myrica rubra) Fruit. Flavonoid Biosynthesis in Bayberry Fruit

To fully elucidate the molecular mechanisms of flavonoid biosynthesis in Chinese bayberry, transcriptomes of two genotypes with different colours, white cultivar (Shuijing, SJ) and red cultivar (Biqi, BQ), were compared. During fruit development, ‘BQ’ exhibited substantial increase of total anthocyanins together with dramatic decrease of total soluble PAs, while ‘SJ’ displayed decrease of total soluble PAs but failed to accumulate anthocyanin. Based on the sequencing results, 124,265 unigenes were generated with an average length of 708 bp. All genes involved in anthocyanin biosynthesis and glycosylation were identified and their expression patterns were in accordance with total anthocyanin accumulation in the developing fruits of ‘BQ’ and ‘SJ’. The expression levels of leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) were down-regulated in ‘SJ’ in agreement with the decrease in PAs, while an opposite trend was observed in ‘BQ’. The higher expression levels of LAR and ANR in ‘BQ’ may be an important reason for the higher levels of total soluble PAs as compared to ‘SJ’. Phylogenetic analysis showed that seven MYBs could be identified as putative homologues of PA-specific regulator and exhibited considerable genotypic and temporal specificity of expression. In addition, three WD40 genes in Chinese bayberry were clustered with the WD40s related to flavonoid biosynthesis in other species. Finally, RNA-Seq data was validated by using RT-qPCR analysis with a high correlation, suggesting that the RNA-Seq data here are credible. These results provide new insights into the regulation of the complex branching pathway leading to various flavonoid compounds biosynthesis in bayberries.