PVX-potyvirus synergistic infections differentially alter microRNA accumulation in Nicotiana benthamiana

In comparison to single infections, co-infection of Nicotiana benthamiana with Potato virus X (PVX) and Potato virus Y (PVY) or Plum pox virus (PPV), resulted in increased systemic symptoms (synergism in pathology). Previous studies have shown that virus infections affected the accumulation of various microRNAs (miRNAs) and miRNA target genes. Our studies revealed that double infection by PVX and PVY or PPV that produced the most severe symptoms in N. benthamiana altered accumulation of miR156, 171, 398, and 168, and/or their target transcripts to a greater extent or in a different direction than single infections that produced milder symptoms. These findings indicate a differential effect on miRNA metabolism of the combined infection by two unrelated plant viruses, which may account in part for the severe symptoms caused by PVX/potyvirus-associated synergisms.