O-GlcNAc modification of the coat protein of the potyvirus Plum pox virus enhances viral infection

• Plum pox virus capsid protein is O-GlcNAcylated.
• New O-GlcNAc-modified sites mapped at the N-terminus of PPV CP.
• O-GlcNAcylation-deficient mutant infects poorly A. thaliana and shows defects in CP stability.
• CP O-GlcNAcylation plays a relevant host-dependent role in PPV infection.

O-GlcNAcylation is a dynamic protein modification which has been studied mainly in metazoans. We reported previously that an Arabidopsis thaliana O-GlcNAc transferase modifies at least two threonine residues of the Plum pox virus (PPV) capsid protein (CP). Now, six additional residues were shown to be involved in O-GlcNAc modification of PPV CP. CP O-GlcNAcylation was abolished in the PPV CP7-T/A mutant, in which seven threonines were mutated. PPV CP7-T/A infected Nicotiana clevelandii, Nicotiana benthamiana, and Prunus persica without noticeable defects. However, defects in infection of A. thaliana were readily apparent. In mixed infections of wild-type arabidopsis, the CP7-T/A mutant was outcompeted by wild-type virus. These results indicate that CP O-GlcNAcylation has a major role in the infection process. O-GlcNAc modification may have a role in virion assembly and/or stability as the CP of PPV CP7-T/A was more sensitive to protease digestion than that of the wild-type virus.