A single phosphorylatable amino acid residue is essential for the recognition of multiple potyviral HCPro effectors by potato Nytbr.

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.