Abstract
Potato virus Y (PVY) is the most economically important potato viral pathogen worldwide. We aimed at unraveling the roles of small RNAs (sRNAs) in the complex immune signaling network controlling the establishment of tolerant response of potato cv. Désirée to the virus. We identified and quantified the endogenous miRNAs and phasiRNAs as well as virus-derived sRNAs. We constructed a sRNA regulatory network connecting sRNAs and their targets identified to link sRNA level responses to physiological processes. We discovered an interesting novel sRNAs – gibberellin (GA) regulatory circuit being activated as early as 3 days post inoculation, before viral multiplication can be detected. Increased levels of miR167 and phasiRNA931 were reflected in decreased levels of transcripts involved in GA biosynthesis. Moreover, decreased concentration of GA confirmed this regulation. We have additionally showed that this regulation is salicylic acid dependent as the response of sRNA network was attenuated in salicylic acid-depleted transgenic counterpart NahG-Désirée expressing severe disease symptoms. Moreover, we found that differentially expressed miR6022, which targets leucine-rich-repeat receptor-like kinases, likely links GA signaling with immune responses. Besides downregulation of GA signaling, regulation of several other parts of sRNA network in tolerant Désirée revealed striking similarities to responses observed in mutualistic symbiotic interactions. The intertwining of different regulatory networks revealed here shows how developmental signaling, symptomology and stress signaling are balanced.
