Date: 18th April 2018
Title: Molecular mechanisms of anti-viral defences in plants
Location: Viikki B building, seminar room 4, Latokartanonkaari 7-9
Host: Kristiina Mäkinen
Abstract: RNA silencing functions to regulate gene expression through the action of DICER-like (DCL) and ARGONAUTE (AGO) endoribonuclease proteins. Most plants encode at least four DCL proteins and ten different AGO proteins, which are specialized to function in different RNA silencing-related mechanisms, including antiviral resistance. For example, AGO2 plays an important role in protecting plants against multiple viruses. This includes resistance to Potato virus X (PVX) in Arabidopsis but not Nicotiana benthamiana, despite the latter having a functional AGO2 protein. In investigating the antiviral activities of AGO2 from different species, we have found that the stability of NbAGO2 is compromised by the PVX viral suppressor of RNA silencing, P25, whereas AtAGO2 is not. These results suggest that inter-specific differences in AGO2 plays a role in virus host range determination. To better understand how variability in AGO2 might influence antiviral activity, we have compared the AGO2 sequences of several hundred Arabidopsis ecotypes and investigated the susceptibility of over fifty ecotypes to PVX. We find a very high level of non-synonymous mutations in the AGO2 gene between different ecotypes compared to AGO1, suggesting that this gene has been submitted to selective pressure. Infection assays indicate that susceptibility to PVX is determined by two co-occurring polymorphisms, with approximately half of the tested ecotypes being susceptible to PVX. Our results indicate that natural variation in RNA silencing components may be an important aspect in determining virus susceptibility. Recent results using natural variation in AGO proteins to understand function will be discussed.
Peter Moffett is a full professor in the department of biology (cell and molecular biology) at the University of Sherbrooke. The Moffett research group is interested in plant-pathogen interactions in general, with a main focus on studying how plants defend themselves against viruses. This includes the study of how NB-LRR proteins recognize specific pathogen-encoded proteins and the signalling mechanisms they induce to eliminate viruses. In parallel, they study how plants use RNA silencing components and related RNA processing mechanisms to specifically recognize and eliminate viral RNAs, as well as the mechanisms used by viruses to overcome this defence. In addition, they are investigating natural variation in model and crop species to understand the genetic and mechanistic bases for variation in susceptibility to viruses and viroids and how this might be harnessed for generating disease-resistant plants. Research in the lab uses several model systems, including tobacco, tomato and Arabidopsis to undertake genetic, biochemical, cell and molecular approaches to understanding plant-virus interactions.