School of Biological Sciences, University of Nebraska-Lincoln, 348 Manter Hall, Lincoln, Nebraska 68588-0118, U.S.A.
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Accepted 9 November 2001.
Tomato bushy stunt virus (TBSV) is one of few RNA plant viruses capable of moving systemically in some hosts in the absence of coat protein (CP). TBSV also encodes another protein (p19) that is not required for systemic movement but functions as a symptom determinant in Nicotiana ben-thamiana. Here, the role of both CP and p19 in the systemic spread has been reevaluated by utilizing transgenic N. ben-thamiana plants expressing the movement protein (MP) of Red clover necrotic mosaic virus and chimeric TBSV mutants that express CP of Turnip crinkle virus. Through careful examination of the infection phenotype of a series of mutants with changes in the CP and p19 genes, we demonstrate that both of these genes are required for efficient systemic invasion of TBSV in N. benthamiana. The CP likely enables efficient viral unloading from the vascular system in the form of assembled virions, whereas p19 enhances systemic infection by suppressing the virus-induced gene silencing.
© 2002 The American Phytopathological Society