The roles of proteins encoded by members of the genus Ampelovirus, family Closteroviridae are largely inferred by sequence homology or analogy to similarly located ORFs in related viruses. This study employed yeast two-hybrid and bimolecular fluorescence complementation assays to investigate interactions between proteins of grapevine leafroll-associated virus 3 (GLRaV-3). The p5 movement protein, HSP70 homolog, coat protein, and p20B of GLRaV-3 were all found to self-interact, however, the mechanism by which p5 interacts remains unknown due to the absence of a cysteine residue crucial for the dimerisation of the closterovirus homolog of this protein. Although HSP70h forms part of the virion head of closteroviruses, in GLRaV-3, it interacts with the coat protein that makes up the body of the virion. Silencing suppressor p20B has been shown to interact with HSP70h, as well as the major coat protein and the minor coat protein. The results of this study suggest that the virion assembly of a member of the genus Ampelovirus occurs in a similar but not identical manner to those of other genera in the family Closteroviridae. Identification of interactions of p20B with virus structural proteins provides an avenue for future research to explore the mechanisms behind the suppression of host silencing and suggests possible involvement in other aspects of the viral replication cycle.
Keywords: Ampelovirus; Closteroviridae; bimolecular fluorescence complementation; protein-protein interactions; virion assembly; yeast two-hybrid.