Genomic, Network, and Phylogenetic Analysis of the Oomycete Effector Arsenal

The oomycetes are a class of microscopic, filamentous eukaryotes and include ecologically significant animal and plant pathogens. Oomycetes secrete large arsenals of effector proteins that degrade host cell components, manipulate host immune responses, and induce necrosis, enabling parasitic colonization. In this study, we catalogued the number and evolution of effectors in 37 oomycete species whose genomes have been completely sequenced. Large expansions of effector protein families inPhytophthoraspecies, including glycoside hydrolases, pectinases, and necrosis-inducing proteins, were observed. Species-specific expansions were detected, including chitinases inAphanomyces astaciandPythium oligandrum. Novel effectors which may be involved in suppressing animal immune responses were identified inAp. astaciandPy. oligandrum. Type 2 necrosis-inducing proteins with an unusual phylogenetic history were also located. This work represents an up-to-datein silicocatalogue of the effector arsenal of the oomycetes based on the 37 genomes currently available.