Mechanisms of Bacterial Suppression of AGO1-RISC Activity and of Host Counter-counter Defense
L. NAVARRO (1), O. Thiébeauld (2), M. Charvin (2), F. Yang (3), D. Pontier (4), E. Lastrucci (2), L. Bapaume (2), G. Li (3), T. Lagrange (5), J. Alfano (3) (1) IBENS-CNRS, France; (2) IBENS-CNRS, France; (3) University of Nebraska, U.S.A.; (4) LGDP, France; (5) LGDP, France

Post-Transcription Gene Silencing (PTGS) is an ancestral mechanism of gene regulation that has been extensively characterized as a natural antiviral defense response in plants. This gene regulatory mechanism has more recently been shown to contribute to resistance against phytopathogenic bacteria, fungi and oomycetes suggesting a widespread antimicrobial defensive role of PTGS in plants.  More specifically, microRNAs (miRNAs) have emerged as central regulators of antibacterial defense in both plants and animals. For instance, several Arabidopsis miRNAs were shown to orchestrate positively or negatively Pattern-Triggered Immunity (PTI). The Arabidopsis miRNA pathway was additionally shown to play a critical role in PTI and, as a corollary, several bacterial effectors from the virulent Pseudomonas syringae pv. tomato strain DC3000 (Pto DC3000) were found to suppress this small RNA pathway to cause disease. However, the modes of action of such bacterial suppressors of RNA silencing (BSRs) remain elusive. Here, I will present the mechanisms by which two BSRs from Pto DC3000 have evolved to directly suppress the activity of AGO1, a central component of the miRNA-Induced Silencing complex (miRISC) that plays a key role in PTI. I will additionally describe a sophisticated mechanism by which plants recognize the presence of these BSRs and in turn counteract their silencing- and PTI-suppression effects.  

Abstract Number: C17-4, P9-331
Session Type: Concurrent