The accumulations of viral RNA and siRNA in dark green and yellow tissues of mosaic leaves of Nicotiana benthamiana inoculated with a Japanese isolate (HM) or a European isolate (PSI4) of the plum pox virus strain M were compared. The accumulation of viral RNA was suppressed in the dark green tissue, but the accumulation of siRNA was higher, similarly in both strains. When the proportion of dark green areas in the five systemic leaf positions from the 9th to the 13th leaf of N. benthamiana was

more »

... ompared between the strains, the result was significantly higher in HM at all leaf positions, reaching 100% in the 13th leaf. Comparison of the amino acid sequence of the RNA silencing suppressor domain in the two strains showed differences in two residues upstream of N' terminus of the FRNK motif in that.