Reaction of three potato cultivars to potato virus S and alteration of miRNAs and mRNA targets in the resistant genotypes

Reactions of three Polish potato cultivars to potato virus S (PVS) were investigated at 22 degrees C. Cultivars Tajfun and Tonacja exhibited partial resistance with systemic infection detected in some inoculated plants; cultivar Bryza was susceptible to PVS with systemic infection detected in all inoculated plants. The virus was not detectable by ELISA at 23 days postinoculation (dpi) but was detected after 40 dpi. Infection rate and viral accumulation were significantly lower in Tonacja and Tajfun than in Bryza, but no statistically significant difference between Tajfun and Tonacja was detected. Both susceptible and resistant genotypes displayed various, either common or cultivar-specific, symptoms. Delayed systemic infection at 56 dpi was observed in some cases in Tonacja and Tajfun. Resistance-related alteration of a set of miRNAs and mRNA targets in the tested cultivars in response to PVS at 22 degrees C exhibited inter- and intracultivar variability. The majority of tested genes were altered only in the partially resistant Tajfun and Tonacja but not in the susceptible Bryza. Enhanced expression of AGO1-2, DCL1, stu-miR482 and its target Gpa2 was observed in Tonacja and plants of Tajfun in which PVS was detected, with the highest induction of Gpa2 in Tajfun (30.2-fold). However, their expression remained unchanged or decreased in plants of Tajfun in which PVS was undetected. Increased expression of stu-miR168a and stu-miR172e was observed in Tonacja and the PVS-undetected plants of Tajfun, respectively, but not in the PVS-detected plants of Tajfun. This is the first report on cultivar-specific alteration of miRNA in a potato-PVS resistance interaction.