Limitations to tobacco mosaic virus infection of turnip

Turnip vein-clearing virus (TVCV) and tobacco mosaic virus (TMV) represent subgroups of tobamoviruses infecting cruciferous and solanaceous plants, re spectively. To identify adaptations that may have been necessary in the evo lution of the TVCV subgroup from a TMV-like ancestor, the infection of turn ip plants by TMV and by chimeras between TMV and TVCV was explored. TMV acc umulated at spatially limited sites on inoculated turnip leaves as determin ed by leaf skeleton hybridization. A plasmid DNA containing a complete TVCV cDNA, when transcribed in vitro, produced RNA that was infectious to tobac co and turnip plants. TVCV-TMV chimeric genomes with junctions within codin g regions were not infectious to tobacco, though the movement protein (MP) chimera was infectious to tobacco with a TMV MP transgene. Reciprocal chime ras with junctions between genes were infectious to tobacco. TVCV with a TM V MP gene infected turnips. The other tested chimeras were not detected in non-inoculated leaves, but were found in the inoculated leaves. Thus, the T MV MP is not responsible for the limitation of TMV spread in turnips.