VIRUS-RESISTANCE IN NICOTIANA-BENTHAMIANA CONFERRED BY AFRICAN CASSAVA MOSAIC-VIRUS REPLICATION-ASSOCIATED PROTEIN (AC1) TRANSGENE

The replication-associated protein AC1 of the bipartite geminivirus Af rican cassava mosaic virus (ACMV) is essential for viral DNA replicati on, Transient expression of ACI 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 ha ve been transformed with the ACI coding sequence cloned downstream of the enhanced cauliflower mosaic virus 35S promoter, Five lines produce d detectable levels of the appropriate-sized ACI-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 ACM V infection; the majority of plants either remained asymptomatic or pr oduced 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 trans formed lines, None of the transformed lines showed resistance to the r elated geminiviruses tomato golden mosaic virus and beet curly top vir us, demonstrating the specific nature of the interaction. Possible mec hanisms for the resistance phenomenon are discussed.