Elicitor-induced phytoalexin synthesis in soybean cells: changes in the activity of chalcone synthase mRNA and the total population of translatable mRNA.

Rapid changes in the mRNA activity encoding chalcone synthase, a central enzyme involved in isoflavonoid phytoalexin synthesis, were induced in cultured cells of soybean (Glycine max) after treatment with a glucan elicitor from the cell walls of the fungus, Phytophthora megasperma f. sp. glycinea, a soybean pathogen. Two-dimensional gel electrophoresis of the in vitro- and in vivo-synthesized chalcone synthase showed that it consisted of a group of proteins of similar molecular weights of about 41,000, but with differing isoelectric points between pH 6.1 and pH 7.1. Total activity of chalcone synthase mRNA increased as early as 40 to 60 min after the onset of elicitor induction, and reached a peak at about 4 h. Treatment with the fungal elicitor caused major changes in the population of total translatable RNA as indicated by two-dimensional electrophoresis of the translation products. The mRNA activities for at least 16 proteins were increased and for at least 4 proteins were decreased. The elicitor-induced changes in the population of translatable mRNA occurred at a rate similar to that observed for chalcone synthase mRNA activity. Our results suggest that soybean cells respond to the glucan elicitor by major metabolic changes at the RNA level including the enhanced capacity for phytoalexin synthesis.