Elicitor rapidly induces chalcone synthase mRNA in Phaseolus vulgaris cells at the onset of the phytoalexin defense response

DNAs complementary to poly(A)(+) RNA present in elicitor-treated cells of Phaseolus vulgaris L. were inserted into pBR325 and used to transform Escherichia coli strain JA221. A clone was identified that contained sequences complementary to mRNA encoding chalcone synthase, a regulatory enzyme of phenylpropanoid biosynthesis, which catalyzes the first reaction of a branch pathway specific to flavonoid and isoflavonoid biosynthesis. Rapid, marked but transient increases in chalcone synthase mRNA in response to elicitor treatment were observed by RNA blot hybridization with (32)P-labeled chalcone synthase cDNA sequences. Induction of chalcone synthase mRNA governs the rate of enzyme synthesis throughout the phase of rapid increase in enzyme activity at the onset of accumulation of isoflavonoid-derived phytoalexins. The data are consistent with the hypothesis that elicitor causes a rapid transient stimulation of transcription of chalcone synthase gene(s) as an early event in the expression of the phytoalexin defense response.