Independent of a direct role in aphid transmission, cellulose synthase and the other virus-associated host proteins may help to orchestrate virion functions in planta. Most plant viruses, including CYDV-RPV, move from cell-to-cell in host plants via plasmodesmata (PD, reviewed in [61] . Luteovirids are targeted to PD early during infection [62] . PD permeability is regulated by carbohydrate metabolism via callose deposition [63] . Callose turnover regulates PD size exclusion limit, as ectopic expression of m-type thioredoxin that is expressed in non-green plastids, which controls callose deposition, causes an increase in plasmodesmal permeability [63] . For cell-to-cell movement, plant viruses have evolved specialized mechanisms to tap into the plants endogenous system for controlling PD permeability for their own cell-to-cell transport. We propose cellulose synthase may be involved in modification of the cell-wall encasing the specialized PD to assist in cell-to-cell virion translocation. A number of other plant viruses have been known to directly interact with and use host enzymes involved in carbohydrate breakdown for cell-to-cell movement through plasmodesmata [21, 64, 65] . Susceptibility to virus infection is decreased in a class I beta-1,3-glucanase-deficient mutant of tobacco generated by stable transformation of tobacco with an antisense construct. The mutant exhibited delayed intercellular trafficking via PD of a tobamovirus (tobacco mosaic virus), of a potexvirus (potato virus X), and of the movement protein 3a of a cucumovirus (cucumber mosaic virus), as well displayed alterations in callose deposition. Through interactions with host beta-1,3 glucanase, the triple gene block protein of PVX, TGB 12 modulates plasmodesmal permeability, probably to mediate cellto-cell spread [66] . Viruses that move from cell-to-cell as ribonucleoproteins (RNPs) also recruit cell-wall modifying enzymes for cell-to-cell movement [64] , suggesting that enzymatic modulation of cell wall carbohydrates to alter PD permeability is a strategy widely used by plant viruses for intercellular trafficking.