Grapevine leafroll disease (GLD) is a globally important disease that affects the metabolic composition and biomass of grapes, leading to a reduction in grape yield and quality of wine produced. Grapevine leafroll-associated virus 3 (GLRaV-3) is the main causal agent for GLD. This study aimed to identify protein-protein interactions between GLRaV-3 and its host. A yeast two-hybrid (Y2H) library was constructed from Vitis vinifera mRNA and screened against GLRaV-3 open reading frames encoding structural proteins and those potentially involved in systemic spread and silencing of host defense mechanisms. Five interacting protein pairs were identified, three of which were demonstrated in planta. The minor coat protein of GLRaV-3 was shown to interact with 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase 02, a protein involved in primary carbohydrate metabolism and the biosynthesis of aromatic amino acids. Interactions were also identified between GLRaV-3 p20A and an 18.1-kDa class I small heat shock protein, as well as MAP3K epsilon protein kinase 1. Both proteins are involved in the response of plants to various stressors, including pathogen infections. Two additional proteins, chlorophyll a-b binding protein CP26 and a SMAX1-LIKE 6 protein, were identified as interacting with p20A in yeast but these interactions could not be demonstrated in planta. The findings of this study advance our understanding of the functions of GLRaV-3-encoded proteins and how the interaction between these proteins and those of V. vinifera could lead to GLD.
Keywords: 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase; Closteroviridae; MAP3K epsilon protein kinase; bimolecular fluorescence complementation; pathogenesis-related proteins; small heat shock protein; virus–host interactions; yeast two-hybrid.