Elicitor induction of mRNA activity. Rapid effects of elicitor on phenylalanine ammonia-lyase and chalcone synthase mRNA activities in bean cells.

Changes in the activity levels of mRNAs encoding phenylalanine ammonia-lyase and chalcone synthase, two characteristic enzymes of phenylpropanoid biosynthesis, in elicitor-treated cells of dwarf French bean (Phaseolus vulgaris L.) have been investigated by immunoprecipitation of [35S]methionine-labelled enzyme subunits synthesised in vitro in an mRNA-dependent rabbit reticulocyte lysate translation system. Elicitor heat-released from cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of bean, causes marked rapid increases in the polysomal activities of the mRNAs encoding the two enzymes concomitant with the phase of rapid increase in enzyme activity at the onset of phaseollin accumulation during the phytoalexin defence response. Increased polysomal mRNA activities encoding the two enzymes can be observed 30 min after elicitor treatment. The patterns of induction of the mRNA activities are broadly similar with respect to time and elicitor concentration although small but distinct differences between the enzymes were observed in the elicitor concentration giving maximum induction. There is a close correlation between the induction of polysomal mRNA activity and the induction of enzyme synthesis in vivo by elicitor treatment with respect to both the kinetics of induction and the dependence on elicitor concentration. The data indicate that elicitor stimulation of phenylalanine ammonia-lyase and chalcone synthase synthesis in vivo is largely a result of increased polysomal activity of the mRNAs encoding these enzymes. Similar patterns of induction of polysomal mRNA activity are observed with elicitor preparations from a variety of sources. The marked increases in polysomal mRNA activities encoding phenylalanine ammonia-lyase and chalcone synthase are increases as a proportion of total cellular mRNA activity, indicating that elicitor does not increase these polysomal mRNA activities by stimulation of selective recruitment from the total pool of cellular mRNA.