A basic helix loop helix transcription factor, AaMYC2-Like positively regulates artemisinin biosynthesis in Artemisia annua L.

Abstract

Artemisinin based combination therapies are still an extensively used remedy for the cure of Malaria. Although artemisinin biosynthetic pathway has been fully worked out, only few information is available on its regulatory mechanism in plants. In the present study, a new member of MYC type basic helix loop helix transcription factor was isolated from Artemisia annua and named as, AaMYC2-Like. The deduced protein sequence of AaMYC2-Like confirmed the presence of conserved DNA binding, dimerization, nuclear localization and helix loop helix domains. The expression analysis of AaMYC2-Like in various tissues established the highest transcript levels in leaves and lowest in roots which were in accordance with the trichome density, the biofactories for artemisinin biosynthesis. Moreover AaMYC2-Like was induced in presence of methyl jasmonate (MeJA), abscisic acid 2,4-dichlorophenoxy acetic acid, methyl viologen, heat, cold etc. The maximum elicitation of AaMYC2-Like transcript levels in presence of MeJA as compared to other phytohormones confirmed AaMYC2-Like as jasmonic acid responsive MYC type transcription factor. Further AaMYC2-Like was found to be transcriptionally active protein and localized to the nucleus. The transient overexpression of AaMYC2-Like in Artemisia annua leaves increased transcript levels of three key enzymes involved in artemisinin biosynthetic pathway such as cytochrome P-450 dependent hydroxylase, double bond reductase and aldehyde dehydrogenase. Consequently artemisinin content was also dramatically elevated in transiently over expressing AaMYC2-Like transgenic plants, confirming prominent role of AaMYC2-Like in the regulation of key biosynthetic genes. Taken together these results strongly suggest that AaMYC2-Like is an important MYC homolog which plays prominent role in the regulation of artemisinin biosynthetic pathway.