Involvement of the octadecanoid pathway and protein phosphorylation in fungal elicitor-induced expression of terpenoid indole alkaloid biosynthetic genes in Catharanthus roseus

Two key genes in terpenoid indole alkaloid biosynthesis, Tdc and Str, encod ing tryptophan decarboxylase and strictosidine synthase, respectively, are coordinately induced by fungal elicitors in suspension-cultured Catharanthu s roseus cells. We have studied the roles of the jasmonate biosynthetic pat hway and of protein phosphorylation in signal transduction initiated by a p artially purified elicitor from yeast extract. In addition to activating Td c and Str gene expression, the elicitor also induced the biosynthesis of ja smonic acid. The jasmonate precursor Lu-linolenic acid or methyl jasmonate (MeJA) itself induced Tdc and Str gene expression when added exogenously. D iethyldithiocarbamic acid, an inhibitor of jasmonate biosynthesis, blocked both the elicitor-induced formation of jasmonic acid and the activation of terpenoid indole alkaloid biosynthetic genes. The protein kinase inhibitor K-252a abolished both elicitor-induced jasmonate biosynthesis and MeJA-indu ced Tdc and Sfr gene expression. Analysis of the expression of Sfr promoter /gusA fusions in transgenic C. roseus cells showed that the elicitor and Me JA act at the transcriptional level. These results demonstrate that the jas monate biosynthetic pathway is an integral part of the elicitor-triggered s ignal transduction pathway that results in the coordinate expression of the Tdc and Sfr genes and that protein kinases act both upstream and downstrea m of jasmonates.