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Virus resistance in Nicotiana benthamiana conferred by African cassava mosaic virus replication-associated protein (AC1) transgene

Hong, Y., Stanley, J.
Molecular plant-microbe interactions 1996 v.9 no.4 pp. 219-225
Nicotiana, African cassava mosaic virus, structural genes, DNA-binding proteins, viral proteins, gene transfer, transgenic plants, gene expression, genetic resistance, DNA replication, Beet curly top virus, Tomato golden mosaic virus
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 AC1 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 geminiviruses tomato golden mosaic virus and beet curly top virus, demonstrating the specific nature of the interaction. Possible mechanisms for the resistance phenomenon are discussed.