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A novel dsRNA virus stimulates sporulation of Phytophthora infestans and may have contributed to late blight epidemics

Guohong Cai: USDA-ARS / Purdue University

<div><em>Phytophthora infestans</em> is the causal agent of potato and tomato late blight. To identify genetic elements contributing to this disease, several dsRNA viruses have been characterized in this organism. One of the viruses, Phytophthora infestans RNA virus 2 (PiRV-2), is 11,170bp in length and without a polyA tail. It contains a large open reading frame (ORF) with short 5’- and 3’- untranslated regions. The ORF is predicted to encode a polyprotein of 3710 aa (calculated molecular weight 410.94 kDa). This virus lacks significant similarity to any known viruses, even in the RNA-dependent RNA polymerase region. Phylogenetic analysis showed it should be classified into a new virus family. Comparing isogenic strains with or without the virus demonstrated that the virus stimulated sporangia production multiple folds. This virus was faithfully transmitted through asexual reproduction and was found in most strains in the US-8 and US-22 lineages. It may have contributed to the success of these two lineages in recent late blight epidemics. This is the first report that a potential hypervirulent virus may contribute to late blight epidemics and presents a novel target for late blight control. <em> </em></div>