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

Abstract 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.