GEMINIVIRUS RESISTANCE IN TRANSGENIC TOBACCO EXPRESSING MUTATED BC1 PROTEIN

Tobacco explants were transformed by Agrobacterium-mediated transforma tion with sense and antisense constructs of the movement protein genes (BC1 and BV1) of tomato mottle geminivirus (TMoV), Transgenic plants were tested for virus resistance either by exposure to viruliferous wh iteflies carrying TMoV or cabbage leaf curl geminivirus (CabLCV) for a 72-h inoculation period or by continuous exposure to TMoV during the life of the plants. The transgenic lines were scored for disease sympt oms, and virus replication and distribution were determined by enzyme- linked immunosorbent assay and dot blot hybridizations. Transgenic pla nts which expressed a mutated form (identified in a previous study) of the BC1 gene showed TMoV and CabLCV resistance, Three resistant pheno types were observed: a delay in symptom development, a recovery from e arly symptoms, and an absence of virus symptoms at all stages. Geminiv irus was detected in inoculated leaves but was not readily detected in leaves beyond the inoculation sites in the highly resistant plants, T he geminivirus resistance conferred by expression of the spontaneously mutated BC1 gene (detected after transformation) in transgenic tobacc o may involve transdominant negative interference.