PiRV-2 stimulates sporulation in Phytophthora infestans.

Phytophthora infestans is the causal agent of potato and tomato late blight. This pathogen, which caused the Irish potato famine, is of profound historical significance and still poses a major threat in today's agroecosystems. Research on late blight epidemics usually focuses on pathogen virulence, host resistance, environmental factors and fungicide resistance. In this study, we examined the effect of PiRV-2, an RNA virus harbored by some P. infestans isolates, on its host. Comparing isogenic isolates with or without the virus demonstrated that the virus stimulated sporangia production in P. infestans. Transcriptome analysis suggested that it achieved sporulation stimulation likely through down-regulation of ammonium and amino acid intake in P. infestans. Survey of a limited P. infestans collection found PiRV-2 presence in most strains in the US-8 lineage, a very successful clonal lineage of P. infestans in North America. We suggest that PiRV-2 may affect the ecological fitness of P. infestans and thus could contribute to late blight epidemiology.