Molecular analysis of ARGONAUTE7 function

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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.