Molecular analysis of ARGONAUTE7 function

反式作用小干扰RNA（Trans-acting small interfering RNAs，ta-siRNAs）是一类植物特异性小分子调控RNA。来自TAS 3前体的Ta-siRNA通过调节生长素应答转录因子的丰度来控制叶极性和根发育。TAS 3前体被Argonaute蛋白AGO 7及其相关microRNA miR 390形成的复合物切割。该复合物引发TAS 3通过RNA依赖性RNA聚合酶RDR 6和SGS 3转化为双链（ds）RNA。然后通过DCL 4加工所得dsRNA以释放ta-siRNA。尽管该途径是植物界最保守的小RNA途径之一，但将AGO 7切割的TAS 3前体路由到RDR 6/SGS 3的机制尚不清楚。几个证据指向AGO 7/miR 390复合物对于将TAS 3路由到RDR 6/SGS 3的关键作用。考虑到TAS 3途径的古老性和在TAS 3加工中对AGO 7的排他性需求，AGO 7很可能在生化水平上亚功能化。在这里，我们建议使用ProDoSS我们开发的创新方法来确定AGO 7的结构-功能关系，并确定其相互作用的伙伴。这将破译AGO 7如何工作，并将确定一些RNA从RNA降解途径转移到RDR/DCL的机制。这些知识对于理解RNA质量控制和沉默机制如何共存和相互作用至关重要。

Trans-acting small interfering RNAs (ta-siRNAs) are plant-specific small regulatory RNAs. Ta-siRNAs from the TAS3 precursor control leaf polarity and root development by modulating the abundance of auxin response transcription factors. The TAS3 precursor is cut by a complex formed by the ARGONAUTE protein AGO7 and its associated microRNA miR390. This complex primes TAS3 for conversion into double stranded (ds)RNA by the RNA-dependent RNA polymerase RDR6 and SGS3. The resulting dsRNA is then processed by DCL4 to release the ta-siRNAs. Although this pathway is among the most conserved small RNA pathways of the plant kingdom, the mechanism routing AGO7-cleaved TAS3 precursor to RDR6/SGS3 is unknown. Several evidences point toward a crucial role of the AGO7/miR390 complex for the routing of TAS3 to RDR6/SGS3. Given the antiquity of the TAS3 pathway and the exclusive requirement for AGO7 in TAS3 processing, it is likely that AGO7 has subfunctionalized at the biochemical level. Here we propose to determine the structure-function relationships for AGO7 using ProDoSS an innovative approach we developed and to identify its interacting partners. This will decipher how AGO7 works and will identify the mechanisms by which some RNAs are diverted from the RNA degradation pathway and routed to RDR/DCL. This knowledge is fundamental to understand how RNA quality control and silencing mechanisms co-exist and inter-operate.