UV-B-induced signaling events leading to enhanced-production of catharanthine in Catharanthus roseus cell suspension cultures

Here, we investigate whether cell surface receptors, medium alkalinization, Ca2+ influx, H2O2, CDPK and MAPK play required roles in UV-B signaling leading to enhanced production of catharanthine in C. roseus cell suspension cultures. C. roseus cells were pretreated with various agonists and inhibitors of known signaling components and their effects on the accumulation of Tdc and Str transcripts as well as amount of catharanthine production were investigated by various molecular biology techniques. It has been found that the catharanthine accumulation and transcription of Tdc and Str were inhibited by 3–4 fold upon pretreatment of various inhibitors like suramin, N-acetyl cysteine, inhibitors of calcium fluxes, staurosporine etc.Our results demonstrate that cell surface receptor(s), Ca2+ influx, medium alkalinization, CDPK, H2O2 and MAPK play significant roles in UV-B signaling leading to stimulation of Tdc and Str genes and the accumulation of catharanthine in C. roseus cell suspension cultures. Based on these findings, a model for signal transduction cascade has been proposed.C. roseus produces terpenoid indole alkaloids (TIAs) as a part of its secondary metabolism. TIAs provide protection against microbial infection, herbivores and abiotic environmental stresses such as UV irradiation [1,2]. Some of the TIAs are of pharmaceutical importance such as the antitumor dimeric alkaloids, vincristine and vinblastine, and the anti-hypertensive monomeric alkaloids, ajmalicine and serpentine [3]. The anti-tumor dimeric alkaloids, which accumulate in the leaves of C. roseus, are composed of catharanthine and vindoline monomers and are exclusively found in C. roseus plants. In plants, the dimeric alkaloids and the monomer catharanthine accumulate in low amounts whereas the monomer vindoline accumulates at a relatively higher level [4,5]. C. roseus cell cultures have been investigated as alternative means of production of terpenoid indole alkaloids, but they failed to produce v