PVX plant expression vector used for subcloning of CPs from different strains of PPV. M1 to M3, movement protein genes, 35S, 35S promoter of CaMV; nosA, nopalin synthetase gene polyadenylation signal; pA-CaMV, polyadenylation signal of CaMV; SGP, subgenomic CP promoter of PVX, A(17), poly(A) tail.