NPR1 and viral infectious disease: A lack of noticeable change in the expression level of the NPR1 gene (in contrast to an increase in the expression level of the PR-1b gene) was observed at 4 hpi in ToMV-infected plants not treated with any inducer, which may suggest that viral infection induces PR-1b gene expression in N. tabacum after the first few hours post infection in an NPR1-independent manner.