CURLY LEAF regulates micro RNA activity by controlling ARGONAUTE 1 degradation in plants

Abstract

CURLY LEAF (CLF) encodes the methyl-transferase sub-unit of the PolycombRepressor Complex 2 (PRC2), which regulates the expression of target genesthrough H3K27 tri-methylation. We isolated a new CLF mutant allele (clf-78)using a genetic screening designed to identify micro RNAs (miRNA) deficientmutants. CLF mutant plants showed impaired miRNA activity caused byincreased AGO1 ubiquitination and enhanced degradation in specific tissues.Such CLF-mediated AGO1 regulation was evidenced when plants wereexposed to UV radiation, causing increased susceptibility of clf mutants to someUV-induced responses. Furthermore, we showed that CLF directly regulatesFBW2, which in turn triggers AGO1 degradation in the mutants. Interestingly,AGO1 bound to a target appeared particularly prone to degradation in themutant plants, a process that is exacerbated when the complex bound a noncleavable target. Thus, a prolonged AGO1-target interaction seems to favorAGO1 degradation, suggesting that non-cleavable miRNA targets mayovercome translation inhibition by modulating AGO1 stability in plants.