Stochastic and nonstochastic post-transcriptional silencing of chitinase and beta-1,3-glucanase genes involves increased RNA turnover - Possible rolefor ribosome-independent RNA degradation

Stochastic and nonstochastic post-transcriptional gene silencing (PTGS) in Nicotiana sylvestris plants carrying tobacco class I chitinase (CHN) and be ta-1,3-glucanase transgenes differs in incidence, stability, and pattern of expression. Measurements with inhibitors of RNA synthesis (cordycepin, act inomycin D, and alpha-amanitin) showed that both forms of PTGS are associat ed with increased sequence-specific degradation of transcripts, suggesting that increased RNA turnover may be a general feature of PTGS. The protein s ynthesis inhibitors cycloheximide and verrucarin A did not inhibit degradat ion of CHN RNA targeted for PTGS, confirming that PTGS-related RNA degradat ion does not depend on ongoing protein synthesis. Because verrucarin A, unl ike cycloheximide, dissociates mRNA from ribosomes, our results also sugges t that ribosome-associated RNA degradation pathways may not be involved in CHN PTGS.