Genetic analysis of the cell-to-cell movement of beet yellows closterovirus

A beet yellows closterovirus (BYV) variant expressing green fluorescent pro tein and leaves of BW local lesion host Claytonia perfoliata were used to r eveal genetic requirements for BMI cell-to-cell movement in leaf epidermis and mesophyll. A series of mutations targeting genes that are not involved in amplification of the viral positive-strand RNA was analyzed. The product s of genes coding for a 6-kDa hydrophobic protein (p6) and a 64-kDa protein (p64), as well as for minor and major capsid proteins, were found to be es sential for intercellular translocation of BW. In a previous work, we have demonstrated that the BYV HSP70-homolog (HSP70h) also plays a critical role in viral movement (V. V. Peremyslov, Y. Hagiwara, and V. V. Dolja, 1999, P roc. Natl. Acad. Sci. USA, 96, 14771-14776). Altogether, a unique protein q uintet including three dedicated movement proteins (p6, p64, and HSP70h) an d two structural proteins is required to potentiate the cell-to-cell moveme nt of a closterovirus. The corresponding BYV genes are clustered in a block that is conserved among diverse representatives of the family Closteroviri dae. (C) 2000 Academic Press.