Analysis of iridoids content and expression studies of genes encoding early enzymes in the indol terpenoid biosynthesis pathway in Catharanthus roseus

Terpenoid indole alkaloids (TIA) are of pharmaceutical importance, however the industrial use of these compouds is very limited because its accumulation is very low in plant tissues. TIA are derived f rom the shikimate and terpenoid pathways, which supply secologanin and tryptamine, the indole and iridoid moieties, respectively. Secololganin is a terpenoid which is belived to be synthesised the MEP pathway rather than by the acetate/mevalonic acid pathway. Secologanin is thought to be a limiting molecule in the biosynthesis of TIAs. Levels of loganic acid, loganin and secologanin were measured by HPLC using tissue derived from different parts of Catharanthus roseus plants. Higher levels of secologanin were found in second pair of leaves. Transcript levels of genes encoding enzymes involved in the early steps of the iridoid pathway were also monitored by northern blots of RNA f rom C. roseus plants. The effect of the elicitor molecule methyl jasmonate in the transcription of genes was also studied. The results obtained in the present work suggest that in young aerial tissues of the plant, the MEP pathway could be more active than the acetate/mevalonic acid pathway. Moreover, there is a clear effect of MeJA in the transcription of the genes studied. Key words: Secondary metabolism, terpenoid indol alcaloids, methyl jasmonate, mevalonate pathway, secologanin