Differential induction of sesquiterpene metabolism in tobacco cell suspension cultures by methyl jasmonate and fungal elicitor

Jasmonates are well documented for their ability to modulate the expression of plant genes and to influence specific aspects of disease/pest resistanc e traits. We and others have been studying the synthesis of sesquiterpene p hytoalexins in elicitor/pathogen-challenged plants and have sought to deter mine if methyl jasmonate (MeJA) could substitute for fungal elicitors in th e induction of capsidiol accumulation by tobacco cell cultures. The current results demonstrate that MeJA does in fact induce phytoalexin accumulation , but with a much more delayed induction time course than elicitor. While e licitor treatment induced strong but transient changes in key enzymes of se squiterpene biosynthesis, sesquiterpene cyclase, and aristolochene/deoxy-ca psidiol hydroxylase, MeJA did not. Instead, MeJA caused a protracted induct ion of cyclase activity and only a low level of hydroxylase activity, MeJA induced the expression of at least two sesquiterpene cyclase genes, includi ng: one that had not been observed previously in elicitor-induced mRNA popu lations, Only a small portion of the total sesquiterpene cyclase mRNA induc ed by MeJA was associated with polysomal RNA, suggesting that the MeJA trea tment imposed both transcriptional and posttranscriptional regulation in to bacco cells, These results are not consistent with MeJA playing a role in o rchestrating defense responses in elicitor-treated tobacco cells, but do pr ovide evidence that MeJA induces a subset of genes coding for the biosynthe sis of sesquiterpene phytoalexins. (C) 2000 Academic Press.