Are the PR1 proteins of tobacco involved in genetically engineered resistance to TMV?

Transgenic tobacco plants constitutively expressing the coat protein (CP) of tobacco mosaic virus (TMV) exhibit enhanced resistance ot TMV (P. Powell Abel, R. S. Nelson, B. De, N. Hoffman, S. G. Rogers, R. T. Fraley, and R. N. Beachy, Science, 232, 738-743, 1986; R. S. Nelson, P. Powell Abel, and R. N. Beachy, Virology 158, 128-132, 1987). To determine if this enhanced resistance might be mediated through the PR1 family of pathogenesis-related (PR) proteins, their synthesis was examined. In transgenic plants derived from NN genotypic tobacco, a high proportion (approximately 80%) of those producing CP also expressed the PR1 genes at low levels. However, this correlation between TMV CP and PR1 gene expression was not observed in similarly transformed nn genotypic tobacco plants. Therefore, it appears unlikely that PR1 proteins play a critical role in genetically engineered resistance in transgenic plants producing TMV CP.