Methyl jasmonate-induced bHLH42 mediates tissue-specific accumulation of anthocyanins via regulating flavonoid metabolism-related pathways in Caitai.

Anthocyanin is a type of plant secondary metabolite beneficial to human health. The anthocyanin content of vegetable and fruit crops signifies their nutritional quality. However, the molecular mechanism of anthocyanin accumulation, especially tissue-specific accumulation, in Caitai, as well as in other Brassica rapa varieties, remains elusive. In the present study, taking advantage of three kinds of Caitai cultivars with diverse colour traits between leaves and stems, we conducted a comparative transcriptome analysis and identified the molecular pathway of anthocyanin biosynthesis in Caitai leaves and stems, respectively. Our further investigations demonstrate that bHLH42, which is robustly induced by MeJA, closely correlates with tissue-specific accumulation of anthocyanins in Caitai; bHLH42 upregulates the expression of flavonoid/anthocyanin biosynthetic pathway genes to activate anthocyanin biosynthesis pathway, importantly, overexpression of bHLH42 significantly improves the anthocyanin content of Caitai. Our analysis convincingly suggests that bHLH42 induced by jasmonic acid signalling plays a crucial role in tissue-specific accumulation of anthocyanins in Caitai.