PiRV-2 stimulates sporulation in Phytophthora infestans

Authors: Cai, Guohong; FRY, WILLIAM - Cornell University; HILLMAN, BRADLEY - Rutgers University

Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2019
Publication Date: 7/23/2019
Citation: Cai, G., Fry, W.E., Hillman, B.I. 2019. PiRV-2 stimulates sporulation in Phytophthora infestans. Virus Research. 271:197674. https://doi.org/10.1016/j.virusres.2019.197674.
DOI: https://doi.org/10.1016/j.virusres.2019.197674

Interpretive Summary: Potato late blight has profound historical significance. It caused devastation of potato crops in the 1840s and led to food shortage across Europe. In Ireland, where the poor were overwhelmingly dependent on potato, it gave rise to the Irish potato famine - over one million people died and many more were forced to flee. This disease is caused by the pathogen Phytophthora infestans. It is still a serious threat to today's potato and tomato production, causing billions of dollars in yield loss and control cost. Research on late blight epidemics usually focuses on pathogen virulence, host resistance, environmental factors and fungicide resistance. In this study, we report the unexpected role of an RNA virus, PiRV-2, in late blight epidemics. We presented evidence that the virus made the P. infestans produce more spores and become more virulent. We found that PiRV-2 achieved its effect likely through restriction of nitrogen and ammonium intake by P. infestans. The virus was found in most isolates of a particular population of P. infestans (the US-8) which had been very successful in North America. Taken together, this study showed that PiRV-2 had the potential to make some isolates of P. infestans more aggressive and it could have contributed to late blight epidemics.

Technical Abstract: 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.