Virus Resistance in Nicotiana benthamiana Conferred by African Cassava Mosaic Virus Replication-Associated Protein (ACI)Transgene. Yiguo Hong. Department of Virus Research, John Innes Centre, Colney Lane, Norwich NR4 7UH, U.K. John Stanley Department of Virus Research, John Innes Centre, Colney Lane, Norwich NR4 7UH, U.K. MPMI 9:219-225. Accepted 8 January 1996. Copyright 1996 The American Phytopathological Society.

The replication-associated protein AC1 of the bipartite geminivirus African cassava mosaic virus (ACMV) is essential for viral DNA replication. Transient expression of AC1 or the truncated N-terminal portion of the protein caused a significant reduction in the level of viral DNA replication in Nicotiana tabacum protoplasts. N. benthamiana plants have been transformed with the AC1 coding sequence cloned downstream of the enhanced cauliflower mosaic virus 35S promoter. Five lines produced detectable levels of the appropriate-sized AC1 -specific transcript, although none was able to complement the systemic infection of an ACMV ACI mutant. However, all lines showed some level of resistance to ACMV infection; the majority of plants either remained asymptomatic or produced delayed and attenuated symptoms, and accumulated significantly reduced levels of viral DNA in comparison with infected control plants. In leaf disk assays, viral DNA replication was also reduced in transformed lines. None of the transformed lines showed resistance to the related gem-iniviruses tomato golden mosaic virus and beet curly top virus, demonstrating the specific nature of the interaction. Possible mechanisms for the resistance phenomenon are discussed.