Virus and Host-Specific Adaptations in theBL1andBR1Genes of Bipartite Geminiviruses

Abstract

The host range of individual geminiviruses may be quite narrow, and closely related viruses can exhibit distinct host adaptations. Two such bipartite geminiviruses are bean golden mosaic virus (BGMV) and tomato golden mosaic virus (TGMV). In both, theBL1andBR1genes are required for the spread of virus infection in plants. We have investigated the contributions ofBL1andBR1to host-specific phenotypes of BGMV and TGMV by constructing hybrid viruses in which these coding regions were exchanged. Hybrids were assayed on bean, a good host for BGMV, andNicotiana benthamiana, a good host for TGMV. A BGMV hybrid having TGMVBL1andBR1efficiently infected beans, but elicited attenuated symptoms. InN. benthamiana, this hybrid had slightly increased virulence and DNA accumulation relative to wild-type BGMV. A TGMV hybrid having BGMVBL1andBR1was virulent inN. benthamiana, but elicited attenuated symptoms. However, this hybrid exhibited no gain of function in beans relative to wild-type TGMV. Hybrid viruses with TGMVBL1and BGMVBR1had severely defective phenotypes in either viral or host background. Although exchangingBL1andBR1between BGMV and TGMV did not change host range, some host adaptation of these genes is suggested. However, virus-specific compatibility betweenBL1andBR1is of more importance for viability. Thus, these gene products may act in concert to potentiate virus movement. © 1995 Academic Press. All rights reserved.