Helper component mutations in nonconserved residues associated with aphid transmission efficiency of a pepper isolate of potato virus Y

The aphid transmission properties of a pepper isolate of potato virus Y bel onging to the pathotype 1-2 (PVY 1-2) have been characterized. PW 1-2 was n ot transmitted in plant-to-plant experiments, although purified virus parti cles were efficiently transmitted when supplemented with heterologous helpe r component (HC) of the transmissible isolate PVY 0 AT through membrane acq uisition assays, indicating that its coat protein was functional in transmi ssion. Additionally, virions of PVY 1-2 were able to bind to different HCs in in vitro binding assays. Analysis of the sequence of the PW 1-2 HC gene and comparison with that of PVY 0 AT revealed 19 nucleotide differences, bu t only 2 resulted in amino acid changes, one of which induced a change of c harge. Neither of these two amino acid changes occurred within the cysteine -rich domain, nor did they coincide with conserved motifs of the HC protein known to be involved in aphid transmission and which are present in all kn own potyviruses. However, both changes are located in positions highly cons erved among PVY strains. The possible role of both mutations on the activit y of the PVY 1-2 HC in aphid transmission is discussed.