Differential induction by methyl jasmonate of genes encoding ornithine decarboxylase and other enzymes involved in nicotine biosynthesis in tobacco cell cultures

A cDNA of tobacco BY-2 cells corresponding to an mRNA species which was rap idly induced by methyl jasmonate (MeJA) in the presence of cycloheximide (C HX) was found to encode ornithine decarboxylase (ODC). Another cDNA from a MeJA-inducible mRNA encoded S-adenosylmethionine synthase (SAMS). Although these enzymes could be involved in the biosynthesis of polyamines, the leve l of putrescine, a reaction product of ODC, increased slowly and while the levels of spermidine and spermine did not change following treatment of cel ls with MeJA. However, N-methylputrescine, which is a precursor of pyrrolid ine ring of nicotine, started to increase shortly after MeJA-treatment of c ells and the production of nicotine occured thereafter. The levels of mRNA for arginine decarboxylase (ADC), an alternative enzyme for putrescine synt hesis, and that for S-adenosylmethionine decarboxylase (SAMDC), required fo r polyamine synthesis, were not affected by MeJA. In addition to mRNAs for ODC and SAMS, mRNA for putrescine N-methyltransferase (PMT) was also induce d by MeJA. Unlike the MeJA-induction of ODC mRNA, MeJA-induction of SAMS an d PMT mRNAs were blocked by CHX. The level of ODC mRNA declined after 1 to 4 h following MeJA treatment, while the levels of mRNAs for SAMS and PMT co ntinued to increase. Auxin significantly reduced the MeJA-inducible accumul ation of mRNAs for ODC, SAMS and PMT. These results indicate that MeJA sequ entially induces expression of a series of genes involved in nicotine biosy nthesis by multiple regulatory mechanisms.