Mapping of two O ‐GlcNAc modification sites in the capsid protein of the potyvirus Plum pox virus

A large number of O ‐linked N ‐acetylglucosamine ( O ‐GlcNAc) residues have been mapped in vertebrate proteins, however targets of O ‐GlcNAcylation in plants still have not been characterized. We show here that O ‐GlcNAcylation of the N‐terminal region of the capsid protein of Plum pox virus resembles that of animal proteins in introducing O ‐GlcNAc monomers. Thr‐19 and Thr‐24 were specifically O ‐GlcNAcylated. These residues are surrounded by amino acids typical of animal O ‐GlcNAc acceptor sites, suggesting that the specificity of O ‐GlcNAc transferases is conserved among plants and animals. In laboratory conditions, mutations preventing O ‐GlcNAcylation of Thr‐19 and Thr‐24 did not have noticeable effects on PPV competence to infect Prunus persicae or Nicotiana clevelandii . However, the fact that Thr‐19 and Thr‐24 are highly conserved among different PPV strains suggests that their O ‐GlcNAc modification could be relevant for efficient competitiveness in natural conditions.