Transgenic accumulation of two plant virus coat proteins on a single self-processing polypeptide.

An expression cassette based on the highly specific tobacco etch potyvirus (TEV) nuclear inclusion (NIa) proteinase has been developed to produce multiple proteins through the translation of a single self-processing polypeptide. Gene constructs encoding TEV NIa, the tobacco mosaic tobamovirus (TMV) coat protein (CP) and the soybean mosaic potyvirus (SMV) CP were used to develop transgenic tobacco plants. Proper processing of the multifunctional polypeptide was demonstrated, leading to accumulation of separate proteins in planta. Moreover, the viral genes expressed in this way were biologically active and conferred pathogen-derived protection to TMV, TEV and potato potyvirus Y (PVY). Transgenic plants were also derived from gene constructs in which the NIa cleavage site was mutated, resulting in the accumulation of the non-processed polyprotein, as predicted. Although transgenic proteins accumulated in low amounts in all the plant lines analysed, accumulation of the mutant non-processed protein form was greatly increased in plants following infection with TEV, but not TMV, apparently as a consequence of protein stabilization.