Recombination of strain O segments to HC pro‐encoding sequence of strain N of Potato virus Y modulates necrosis induced in tobacco and in potatoes carrying resistance genes Ny or Nc

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Abstract
Summary: Hypersensitive resistance ( HR ) to strains O and C of Potato virus Y ( PVY , genus Potyvirus ) is conferred by potato genes Ny tbr and Nc tbr , respectively; however, PVY N strains overcome these resistance genes. The viral helper component proteinases ( HC pro, 456 amino acids) from PVY N and PVY O are distinguished by an eight‐amino‐acid signature sequence, causing HC pro to fold into alternative conformations. Substitution of only two residues ( K269R and R270K ) of the eight‐amino‐acid signature in PVY N HC pro was needed to convert the three‐dimensional ( 3D ) model of PVY N HC pro to a PVY O ‐like conformation and render PVY N avirulent in the presence of Ny tbr , whereas four amino acid substitutions were necessary to change PVY O HC pro to a PVY N ‐like conformation. Hence, the HCpro conformation rather than other features ascribed to the sequence were essential for recognition by Ny tbr . The 3D model of PVY C HC pro closely resembled PVY O , but differed from PVY N HC pro. HC pro of all strains was structurally similar to β‐catenin. Sixteen PVY N 605 ‐based chimeras were inoculated to potato cv. Pentland Crown ( Ny tbr ), King Edward ( Nc tbr ) and Pentland Ivory ( Ny tbr / Nc tbr ). Eleven chimeras induced necrotic local lesions and caused no systemic infection, and thus differed from both parental viruses that infected K ing Edward systemically, and from PVY N 605 that infected P entland Crown and P entland Ivory systemically. These 11 chimeras triggered both Ny tbr and Nc tbr and, in addition, six induced veinal necrosis in tobacco. Further, specific amino acid residues were found to have an additive impact on necrosis. These results shed new light on the causes of PVY ‐related necrotic symptoms in potato.
Funding Information
  • Suomen Akatemia (1253126)

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