TRANSACTIVATION OF DIANTHIN TRANSGENE EXPRESSION BY AFRICAN CASSAVA MOSAIC-VIRUS AC2

We have recently described a novel strategy for engineering resistance to African cassava mosaic virus (ACMV) in transgenic Nicotiana bentha miana plants using a virus-inducible promoter to control the expressio n of a plant ribosome-inactivating protein (RIP) transgene (Y. Hong et al., Virology 220, 119-127, 1996). Here, we have used a potato virus X (PVX) vector to express the ACMV transactivator protein, AC2, in pla nta. We confirm that amplification of RIP activity in transgenic plant s is mediated by AC2; disruption of AC2 expression by either the intro duction of an in-frame stop codon or the deletion of 5'-terminal or 3' -terminal coding sequences reduced RIP expression to the basal level a ssociated with PVX-infected plants. AC2 expression from the PVX vector induced necrosis in nontransformed plants as well as in plants contai ning the RIP transgene, suggesting that the protein can functionally i nteract with PVX and/or host factors. The potential of this system to provide a direct and sensitive assay to investigate AC2 function in pl anta is discussed. (C) 1997 Academic Press.