CELL-TO-CELL MOVEMENT OF BEET NECROTIC YELLOW VEIN VIRUS - I - HETEROLOGOUS COMPLEMENTATION EXPERIMENTS PROVIDE EVIDENCE FOR SPECIFIC INTERACTIONS AMONG THE TRIPLE GENE BLOCK PROTEINS

Cell-to-cell movement of beet necrotic yellow vein virus (BNYVV) requi res three proteins encoded by a triple gene block (TGB) on viral RNA 2 . A BNYVV RNA 3-derived replicon was used to express movement proteins of other viruses and the ability of these proteins to functionally su bstitute for the BNYVV TGB proteins was tested by coinoculation of TGB -defective BNYVV with the various replicons to Chenopodium quinoa. Tra ns-heterocomplementation was successful with the movement protein (P30 ) of tobacco mosaic virus but not with the tubule-forming movement pro teins of alfalfa mosaic virus and grapevine fanleaf virus. Trans-compl ementation of BNYVV movement was also observed when all three TGB prot eins of the distantly related peanut clump virus were supplied togethe r but not when they were substituted for their BNYVV counterparts one by one. When P30 was used to drive BNYVV movement in tracts, accumulat ion of the first TGB protein of BNYVV was adversely affected by null m utations in the second and third TGB proteins. Taken together, these r esults suggest that highly specific interactions among cognate TGB pro teins are important for their function and/or stability in planta.