Abstract

The looming challenge of feeding the rapidly growing population is threatened by crop losses from plant diseases with an average of 10-15% of the yield being lost to pathogens and pests each year. Although plants have evolved a myriad of immune mechanisms, successful pathogens overcome the defence system and cause disease. The dynamic interplay between virulence factors of a pathogen and the innate immunity of a host determines whether disease will occur. A deep understanding of the molecular mechanisms that underlie host-pathogen interactions is essential for developing durable disease resistance. We have a long-standing interest in the molecular basis of host-pathogen co-evolution. Recent research in my laboratory focuses on plant small RNAs (sRNAs) as a newly emerged battleground in this arms race. Gene silencing guided by sRNAs governs a broad range of cellular processes. We identified a specific family of plant sRNAs that, instead of regulating endogenous gene expression, guide target gene silencing in the invading eukaryotic filamentous pathogen Phytophthora. We show sequences that spawn these antimicrobial sRNAs exhibiting a high level of diversification, consistent with their engagement in antagonistic interactions with pathogens. We also found Phytophthora virulence proteins, called effectors, that suppress host sRNAs as a counter-defence mechanism. Structural analysis of one such effector Phytophthora suppressors of RNA silencing 2 (PSR2) led to the discovery of a unique tandem repeat arrangement that potentially contributes to the evolvability of Phytophthora effectors. I will discuss our recent progress on sRNA-mediated immunity in plants and functional diversification of the effector repertoire in Phytophthora.

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