A single phosphorylatable amino acid residue is essential for the recognition of multiple potyviral HCPro effectors by potato Ny(tbr).

Potato virus Y (PVY, Potyviridae) is among the most important viral pathogens of potato. The potato resistance gene Ny(tbr) confers hypersensitive resistance to the ordinary strain of PVY (PVY(O)), but not the necrotic strain (PVY(N)). Here, we unveil that residue 247 of PVY helper component proteinase (HCPro) acts as a central player controlling Ny(tbr) strain-specific activation. We found that substituting the serine at 247 in the HCPro of PVY(O) (HCPro(O)) with an alanine as in PVY(N) HCPro (HCPro(N)) disrupts Ny(tbr) recognition. Conversely, an HCPro(N) mutant carrying a serine at position 247 triggers defence. Moreover, we demonstrate that plant defences are induced against HCPro(O) mutants with a phosphomimetic or another phosphorylatable residue at 247, but not with a phosphoablative residue, suggesting that phosphorylation could modulate Ny(tbr) resistance. Extending beyond PVY, we establish that the same response elicited by the PVY(O) HCPro is also induced by HCPro proteins from other members of the Potyviridae family that have a serine at position 247, but not by those with an alanine. Together, our results provide further insights in the strain-specific PVY resistance in potato and infer a broad-spectrum detection mechanism of plant potyvirus effectors contingent on a single amino acid residue.