Phylogenetic tree of the selected NPR1 homologs. The deduced amino acid sequences of NPR1 homologs from different plant species were used to construct the tree using the maximum likelihood method with 1000 bootstrap values indicated. The information for the homologs used in the analysis is listed in Additional file 1: Table S2. PhaNPR1 is indicated in bold. Members from the five species with reference genomes were included to identify orthologous groups. Three orthologous groups were identified and named NPR1, NPR3, and BOP. Because the NPR1 and NPR3 groups were closely related, these two groups were joined to form a larger NPR group.