Identification and characterization of suppressors of plant cell death (SPD) effectors from Magnaporthe oryzae.

Phytopathogenic microorganisms including the fungal pathogen Magnaporthe oryzae secrete a myriad of effector proteins to facilitate infection. Utilizing transient expression of candidate effectors in the leaves of the model plant N. benthamiana, we identified 11 suppressors of plant cell death (SPD) effectors from M. oryzae that are able to block the host cell death reaction induced by the Nep1 gene. Ten of these 11 are also able to suppress BAX mediated plant cell death. Five of the eleven SPD genes have been previously identified as either essential for pathogenicity of M. oryzae, secreted into the plant during disease development, or as suppressors or homologues of other characterized suppressors. Additionally, of the remaining six, we show that SPD8 (previously identified as BAS162) is localized to the rice cytoplasm in invaded and surrounding uninvaded cells during biotrophic invasion. Sequence analysis of the 11 SPD genes across 43 re-sequenced M. oryzae genomes revealed SPD2, SPD4, and SPD7 have nucleotide polymorphisms amongst the isolates. SPD4 exhibited the highest level of nucleotide diversity of any currently know effector from M. oryzae in addition to presence/absence polymorphisms, suggesting that this gene is potentially undergoing selection to avoid recognition by the host. Taken together, we have identified a series of effectors, some of which were previously unknown or whose function was unknown, that likely act at different stages of the infection process and contribute to the virulence of M. oryzae. This article is protected by copyright. All rights reserved.