CHANGES IN THE AMINO-ACID-SEQUENCE OF THE COAT PROTEIN READTHROUGH DOMAIN OF POTATO LEAFROLL LUTEOVIRUS AFFECT THE FORMATION OF AN EPITOPE AND APHID TRANSMISSION

Potato leafroll luteovirus (PLRV) is transmitted naturally by aphids, but two isolates (15 and V) are known to be only poorly transmissible (PAT); these isolates are also distinct in that their particles lack a n epitope present in transmissible (HAT) isolates of PLRV (Tamada et a l., Ann. Appl. Biol. 104, 107-116, 1984; Massalski and Harrison, J. Ge n. Virol. 68, 1813-1821, 1987). Virus cultures propagated vegetatively for several years in potato plants from the source of isolate V were shown still to be poorly transmissible by Myzus persicae. Moreover, wh en isolate V was transmitted by aphids, the subisolates obtained (V4 a nd V31) were no more readily transmissible than was the stock culture PLRV-V. The subisolates were also unchanged antigenically by the trans mission. Thus the inefficient transmission had not restored the proper ties of HAT isolates. Sequence comparisons among the coat proteins and the readthrough domains of HAT and PAT Scottish isolates suggested th at either or both of two amino acid changes in the C-terminal part of the readthrough protein are responsible for the poor transmission and the loss of an epitope. The readthrough protein is therefore thought t o play a role in the circulative aphid transmission of PLRV. (C) 1994 Academic Press, Inc.