GENETIC-ANALYSIS OF THE MONOPARTITE TOMATO YELLOW LEAF CURL GEMINIVIRUS - ROLES OF V1, V2, AND C2 ORFS IN VIRAL PATHOGENESIS

Tomato yellow leaf curl virus (TYLCV) is a whitefly-transmitted gemini virus with a monopartite genome. We have investigated the functions of the V1, V2, and C2 ORFs by mutational analysis. We analyzed the abili ty of TYLCV mutants containing disrupted ORFs V1, V2, or C2 to replica te, spread, and cause symptoms in Nicotiana benthamiana and tomato pla nts. All the mutants retained the capability of autonomous replication in protoplast-derived cells of tomato and leaf discs of N. benthamian a, although both V1 and V2 gene products appeared to play a role in th e accumulation of viral single-stranded DNA. In contrast, none of the mutants was able to systemically infect tomato plants, demonstrating t hat the V1, V2, and C2 gene products are all required for a successful infection process in this host. The effect of the mutation in ORF C2 appeared to be host-specific, since N. benthamiana plants were systemi cally infected, although symptom development was attenuated. (C) 1997 Academic Press.