Downregulation of terpenoid indole alkaloid biosynthetic pathway by low temperature and cloning of a AP2 type C-repeat binding factor (CBF) from Catharanthus roseus (L). G. Don.

Plants produce secondary metabolites in response to various external signals. Coordinated transcriptional control of biosynthetic genes emerges as a major mechanism dictating the accumulation of secondary metabolites in plant cells. However, information about stress regulation of secondary metabolites and the molecular mechanisms regulating these specialized pathways are poorly understood. Here, we show that terpenoid indole alkaloid (TIA) biosynthetic pathway is differentially regulated in response to different abiotic stresses in Catharanthus roseus, a model medicinal plant producing important anticancer and antihypertensive drugs. Semiquantitative RT-PCR analysis of TIA and related primary pathway genes in response to dehydration, low temperature, salinity, UV-light and wounding revealed their negative regulation in response to low temperature. HPLC analysis further supports the notion that TIA biosynthetic pathway is negatively controlled by low temperature stress. Furthermore, we report the cloning of a C-repeat binding transcription factor from C. roseus (CrCbf), belonging to AP2 class of transcription factor and possessed the NLS and CBF signature sequence characteristic of CBFs. CrCbf was found to be similar to Brassica Cbfs, whereas it was distant to monocot Cbfs. Southern analysis of CrCbf revealed the presence of more than one copy of CrCbf gene or other Cbf homologues in C. roseus genome. The transcription of CrCbf was found to be constitutive in response to low temperature but it showed differential distribution. The need for identifying novel transcription factors in understanding secondary metabolite biosynthesis is discussed.