CURLY LEAF (CLF) encodes the methyltransferase subunit of the Polycomb Repressor Complex 2 (PRC2), which regulates the expression of target genes through H3K27 trimethylation. We isolated a new CLF mutant allele (clf-78) using a genetic screen designed to identify microRNA (miRNA) deficient mutants. CLF mutant plants showed impaired miRNA activity caused by increased ubiquitination and enhanced degradation of ARGONAUTE 1 (AGO1) in specific tissues. Such CLF-mediated AGO1 regulation was evident when plants were exposed to UV radiation, which caused increased susceptibility of clf mutants to some UV-induced responses. Furthermore, we showed that CLF directly regulates FBW2, which in turn triggers AGO1 degradation in the clf mutants. Interestingly, AGO1 bound to a target appeared particularly prone to degradation in the mutant plants, a process that was exacerbated when the complex bound a non-cleavable target. Thus, prolonged AGO1–target interaction seems to favor AGO1 degradation, suggesting that non-cleavable miRNA targets may overcome translation inhibition by modulating AGO1 stability in plants.

CURLY LEAF（CLF）编码Polycomb Repressor Complex 2（PRC2）的甲基转移酶亚基，它通过H3K27三甲基化调节靶基因的表达。我们使用旨在鉴定microRNA（miRNA）缺陷型突变体的遗传筛选方法分离了一个新的CLF突变体等位基因（clf-78）。CLF突变植物显示出泛素化增强和特定组织中ARGONAUTE 1（AGO1）降解增强导致miRNA活性受损。当植物暴露于紫外线辐射时，这种CLF介导的AGO1调节很明显，这导致clf突变体对某些紫外线诱导的反应的敏感性增加。此外，我们表明CLF直接调节FBW2，进而触发clf突变体中的AGO1降解。有趣的是，与靶标结合的AGO1在突变植物中似乎特别易于降解，当复合物与不可裂解的靶标结合时，这一过程会加剧。因此，延长的AGO1与靶标的相互作用似乎有利于AGO1的降解，这表明不可裂解的miRNA靶标可以通过调节植物中AGO1的稳定性来克服翻译抑制作用。