Immunodetection of the proteins encoded by grapevine chrome mosaic nepovirus RNA2

Fragments of the putative non-structural proteins (44K and 46K) encoded by RNA2 of grapevine chrome mosaic nepovirus (GCMV) were expressed as fusion proteins in Escherichia coli and used to raise specific antisera. All three proteins encoded by GCMV RNA2 (viral coat protein, and the 44K and 46K proteins) were detected by immunoblotting in subcellular fractions prepared from the leaves of infected Chenopodium quinoa plants, confirming a previously proposed model of the GCMV RNA2-encoded polyprotein. In addition to the 44K protein, one of the antisera detected a 90K protein presumably representing a precursor of the 44K and 46K proteins. Whereas the 44K and coat proteins could be detected in both soluble and membrane fractions, the 46K protein was found to be specific to the membrane fraction. Analysis of the kinetics of accumulation of the proteins showed that the 44K and 46K proteins were very transient whereas the coat protein was more stable and could be detected up to 21 days after inoculation. These results provide the first direct in vivo data supporting the maturation map of the GCMV RNA2 polyprotein deduced from in vitro experiments.