Post-transcriptional gene silencing (PTGS) mediated by short interfering RNAs (siRNAs) is an evolutionary conserved antiviral defense mechanism in higher plants and invertebrates. In this process, viral-derived siRNAs are incorporated into the RNA-induced silencing complex (RISC) to guide degradation of the corresponding viral RNA. In Arabidopsis, the key component of RISC is the ARGONAUTE1 (AGO1) protein, that binds siRNA duplexes resulting from the DICERLIKE4/2 (DCL2/4) cleavage activity, and acts by using one strand of the duplex to cleave and/or translationally repress the viral RNA in a sequence specific manner. In planta, AGO1 levels are modulated at both post-transcriptional and translational level, and our work has recently uncovered the importance of ubiquitylation in AGO1 turnover. This process is recapitulated upon infection by the Turnip Yellow Virus (TuYV), which harbors the P0 suppressor of silencing, carrying a F-box motif. During infection, K63 ubiquitylation of AGO1 is carried out by the SCFP0, which ultimately routes AGO1 to the vacuole. Using an inducible P0 transgenic line, we have generated a P0 suppressor screen that allowed us to identify mutants affected in the P0-dependent degradation of AGO1. Here I will present one of these mutants corresponding to an intragenic allele of AGO1, in a previously uncharacterized but conserved domain of the protein. I will also discuss more broadly the importance of AGO1 turnover under normal and stress conditions.
P. Genschik, did his PhD (1994) at the University of Strasbourg (FR) in plant science; Post-doc (1994-1997) at the Friedrich Miescher, Basel (CH), in the field of RNA metabolism in plant and human; Group Leader at IBMP-CNRS in (1998) Strasbourg (FR) and he became the Scientific Director of the Institute (2005-2012). He obtained national and international grants (such as an ERC advanced grant, 2013) and participated in several consortiums including the Network of Excellence (Rubicon). He became also elected EMBO member (2012). His laboratory has a long history of providing new knowledge in the field of post-translational regulation in plants. Amongst others studies, his group unraveled the post-translational mechanisms regulating the stability EIN3 in ethylene signalling, the role of proteolysis of DELLA proteins in GA-signalling), but also the function of selective proteolysis in ABA-signalling. Furthermore, his group characterized several novel E3 ligases that are instrumental for host pathogen responses, maintenance of genome integrity upon UV stress and permitting cell cycle phase transitions. His group is currently focused on a novel mechanism by which viruses hijack the ubiquitin pathway to suppress the host anti-viral silencing response.