Investigation of the potential of Maize streak virus to act as an infectious gene vector in maize plants

There has been a great deal of interest in the possibility that geminivirus es might be used as infectious gene vectors for expression of foreign prote ins in planes. However, generic mastreviruses such as Maize streak virus (M SV) have no sequences which are dispensable for systemic infection of plant s, and there is a strict limitation on the size of viral DNA which can be m oved systemically. We attempted to complement the movement functions delete d from a; wild-type-sized, replication-proficient gene replacement vector, by co-infecting plants with it and either wild type MSV, or a replication-d eficient but putatively movement-proficient viral construct. While ssDNA fo rmation by the gene replacement vector could be complemented in trans by co -transfected wild type virus, true systemic movement of either the vector, or of co-complementing constructs, did not occur. However, recombination be tween the two complementing viral constructs frequently occurred to generat e wild-type virus genomes. The results therefore suggest that formation of ssDNA and size of the viral replicon are not the sole determinants of wheth er the MSV movement proteins can mobilise viral sequences and move them sys temically in plants.