Co-expression of GbMYB1 and GbMYC1 induces anthocyanin accumulation in roots of cultured Gynura bicolor DC. plantlet on methyl jasmonate treatment

Gynura bicolor DC. is a traditional vegetable in Japan. G. bicolor grown in the field has adaxial sides of leaves that are green and abaxial sides that are reddish purple. It has been reported that the responsible reddish purple pigments are anthocyanins, which are acylated and highly stable. We have reported that cultured G. bicolor plantlets treated with methyl jasmonate (MJ) exhibited anthocyanin accumulation in roots, and this was affected by light irradiation. In the present study, to clarify this accumulation induced by MJ treatment, we isolated anthocyanin biosynthesis and regulatory genes from G. bicolor. Expression analysis revealed up-regulated expression of flavonoid biosynthesis genes, GbCHS, GbCHI, GbDFR and GbANS. Furthermore, it was shown that isolated regulatory genes, GbMYB1 and GbMYC1, were also up-regulated by MJ treatment. In addition, it was shown that co-expression of GbMYB1 and GbMYC1 could activate GbDFR and GbANS gene promoters in transient assays with tobacco protoplasts. These results strongly indicate that GbMYB1 and GbMYC1 coordinately regulate flavonoid biosynthetic genes induced by MJ treatment, and thereby cause anthocyanin accumulation in roots.

Research highlights
► Cultured G. bicolor treated by methyl jasmonate (MJ) accumulated anthocyanin in roots.
► Expression of flavonoid biosynthesis genes was up-regulated transcriptionally by MJ.
► Isolated regulatory genes, GbMYB1 and GbMYC1, were also up-regulated by MJ treatment.
► Co-expression of GbMYB1 and GbMYC1 could activate GbDFR and GbANS gene promoters.
► GbMYB1 and GbMYC1 act as regulators for anthocyanin accumulation induced by MJ.