Expression of the coat protein genes of PNRSV and PDV in the synergistic disease peach stunt

Simultaneous infections of peach (Prunus persica Batsch L.) with the two ilarviruses, Prunus necrotic ringspot virus (PNRSV) and Prune dwarf virus (PDV), produce a synergistic disease referred to as “peach stunt”. Previous work showed significant differences in the expression of the coat protein (CP) genes. In the presence of PNRSV, an up to 17- fold reduction in the amount of (+) strand RNA 3 of PDV, as compared to similar trees infected with PDV alone, was observed. However, the presence of PDV had no effect on the concentration of (+) strand RNA 3 of PNRSV (Scott et al., 2001). This work re-examines and extends these observations using multiplex real-time PCR. Probes to both the plus and minus strands of the RNA 3 of each virus were designed and synthesized. The comparative CT method (ΔΔCT) was used for relative quantitation of gene expression. A reduction in the amount of (+) strand RNA 3 of PDV observed in the earlier work was not seen using real-time PCR. However, in a time course experiment with samples collected at 14-day intervals for 6 weeks, there was a substantial increase in the concentration of the (+) strand of RNA 3 of PDV after 14 days irrespective of whether the virus was present as a sole infecting agent or as a co-infection with PNRSV. At this same point in time there was a decrease in concentration of (+) of the RNA 3 of PNRSV. By the next sample date the concentrations of the (+) strand of RNA 3 of both viruses had returned to “normal”. The results are discussed in relation to the most extensively studied plant viral synergism synergism (PVY and PVX) and to known changes in concentration of PNRSV and PDV based on earlier observations made using ELISA.