FUNGAL ELICITOR-INDUCED BEAN PROLINE-RICH PROTEIN MESSENGER-RNA DOWN-REGULATION IS DUE TO DESTABILIZATION THAT IS TRANSCRIPTION AND TRANSLATION DEPENDENT

In bean cells treated with fungal elicitor, the transcripts of PvPRP1, a gene encoding a proline-rich protein, decreased to approximately 6% of the original level within 4 hr. The apparent mRNA half-life during the period of rapid degradation was approximately 45 min. The rate of PvPRP1 gene transcription remained constant over this period, as dete rmined by nuclear run-off assays, indicating a decrease in mRNA stabil ity. By using actinomycin D to block transcription, the half-life of P vPRP1 mRNA in unelicited cells was estimated to be approximately 60 hr . In cells treated with actinomycin D followed by the addition of elic itor, the PvPRP1 mRNA half-life was approximately 18 hr, whereas cells treated with these reagents in reciprocal order exhibited a half-life of approximately 6 hr. The protein synthesis inhibitors emetine and a nisomycin also inhibited the rate of PvPRP1 mRNA degradation in elicit ed cells. Based on these data, we concluded that the rapid decrease in the PvPRP1 mRNA level in elicited cells is due to destabilization, wh ich is dependent on new RNA and protein synthesis.