TOMATO SPOTTED WILT TOSPOVIRUS GENOME REASSORTMENT AND GENOME SEGMENT-SPECIFIC ADAPTATION

A system to associate specific genome segments with viral phenotypes a nd to study factors influencing genome reassortment was developed for tomato spotted wilt Tospovirus (TSWV). Reassortant isolates were gener ated by coinoculating a TSWV isolate, TSWV-D, with TSWV-10 or TSWV-MD. The parental origin of each genome segment in putative reassortant is olates was determined by segment-specific restriction fragment length polymorphisms. The TSWV isolates readily exchanged genome segments in a nonrandom fashion. The S RNA from TSWV-D was dominant over the S RNA from TSWV-10. The intergenic region (IGR) of the S RNA was correlated with competitiveness of this genome segment in reassortant isolates. The less competitive S RNA contained a net increase of 62 nt, includin g a 33-nt duplication in the IGR. This duplicate sequence was highly c onserved among isolates from the southeastern United States and an iso late from Bulgaria. The evidence supports the hypothesis that the IGR of the S RNA with an ambisense coding strategy serves a regulatory fun ction which influences the occurrence of this segment in the viral pop ulation. In addition, it was demonstrated that stable parental phenoty pes can be mapped to specific genome segments as well as generating no vel phenotypes not associated with either parent. (C) 1998 Academic Pr ess.