Molecular studies of the synergistic interactions between plum pox virus HC-Pro protein and potato virus X

Helper component proteinase (HC-Pro) is a multifunctional viral protein involved in vection and movement of potyvirus; suppression of host post-transcriptional gene silencing reaction; and synergism of potyvirus with other viruses, notably potexvirus. When the HC-Pro of plum pox potyvirus (PPV) was transiently expressed in N. benthamiana and N. clevelandii plants via potato virus X (PVX) vector, a highly synergistic response of leaf necrosis or plant death, was observed in PVXHC-infected plants. However, when mutations were introduced into the highly conserved "PTK" and "KITC" motifs of HC-Pro, known for their involvement in protein/protein interaction during aphid-mediated transmission of potyvirus, the resulting change of amino acid residue from lysine (K) to glutamic acid (E) in the "KITC" motif had no obvious influence.