A defective movement protein of TMV in transgenic plants confers resistance to multiple viruses whereas the functional analog increases susceptibility.

Transgenic tobacco plants that express a gene encoding a defective mutant of the tobacco mosaic virus (TMV) movement protein which are known to be resistant to several tobamoviruses were inoculated with viruses from different taxonomic groups to determine the breadth of resistance. There were significant delays in the time of appearance of disease symptoms and/or there was reduced systemic accumulation of virus in upper leaves of plants inoculated with tobacco rattle tobravirus, tobacco ringspot nepovirus, alfalfa mosaic alfamovirus, peanut chlorotic streak caulimovirus, and cucumber mosaic cucumovirus. Conversely, tobacco plants that express a gene encoding the functional tobacco mosaic virus wild-type movement protein accelerated symptom development, enhanced the severity of symptom formation, and/or increased the accumulation of these viruses and, additionally, TMV. Our results indicate that there are similar functions among the movement proteins of a number of plant viruses despite the apparent lack of sequence similarity between them.

RNase protection analyses show high genetic diversity among field isolates of satellite tobacco mosaic virus.

Fifteen field isolates of satellite tobacco mosaic virus (STMV) were collected from wild Nicotiana glauca plants within a 20-km2 area in southern California. Analyses of the entire length of the satellite genomic RNA of each isolate by RNase protection assays showed that there were 10 different genotypes within the 15 isolates, including some with regions of extreme divergence from the STMV type strain. This indicates a very high level of genetic diversity between natural STMV populations. Isolates from adjacent plants (within 3 m) were not always identical, but were more similar than those from more distant locations. Mapping of the genomic sites of heterogeneity revealed that in all cases the 3' half of the genome, which comprises the untranslated region, was more conserved than were the 5' coding regions.