Basic helix-loop-helix transcription factors and regulation of alkaloid biosynthesis.

Transcription factors of the basic Helix-Loop-Helix (bHLH) family play a central role in cell proliferation, determination, and differentiation. In plants, the regulatory functions of bHLHs in phenylpropanoid biosynthesis have been well established with regard to other interacting-proteins; i.e., MYB and WD40 repeat proteins. On the other hand, those in alkaloid biosynthesis are greatly limited due to the limited distribution of alkaloids in plant species. Recently, several groups have reported the regulatory functions of bHLH in alkaloid biosynthesis: novel CjbHLH1 in isoquinoline alkaloid biosynthesis in Coptis japonica, and Jasmonate-inducible MYC2-type bHLHs in nicotine-alkaloid biosynthesis in Nicotiana plants and indole alkaloid biosynthesis in Catharanthus roseus. We report here the JA-inducibility of CjbHLH1 and discuss the similarity and differences of non-MYC2-resemblant CjbHLH1 and MYC2-type bHLHs in nicotine and indole alkaloid biosynthesis.