The StubGAL83 subunit of the StubSNF1 complex interacts with HC-Pro of Potato virus Y and influences virus multiplication in potato

Potyvirus is the largest genus of plant viruses that causes significant losses in a wide range of crops. Potyviruses are transmitted through aphids, and the helper component proteinase (HC-Pro) of the virus is required for transmission. However, HC-Pro is a multifunctional protein that has self-interactions and interactions with other potyviral and host-plant proteins. Here, we report that HC-Pro of the Potato virus Y O strain (PVYO) interacts with the StubSNF1 protein kinase complex regulatory subunit StubGAL83 in a yeast two-hybrid assay. StubSNF1 is an SnRK1 family member of plant proteins that regulates carbon metabolism and stress responses. The HC-Pro interaction site was mapped to amino acid residues 154-187 overlapping the SNF1 binding KIS domain in StubGAL83, while the StubGAL83 interaction site was localised to amino acid residues 50-84 on HC-Pro. This region is involved in the virus transmission process and carries the KITC motif, which has an important role in the interaction with other host proteins, too. We show that PVYO infection down-regulates StubGAL83 expression in the potato cultivar 'Desiré'. Nevertheless, down-regulation of StubGAL83 expression moderates PVYO accumulation in both inoculated and systemic leaves, suggesting that the altered intracellular environment in StubGAL83-repressed lines is not favourable for virus multiplication.