Phylogenetic analysis of plant MAPKKK genes and structural features of novel N. benthamiana MAPKKK genes. A) Phylogenetic tree for the kinase domain-encoding regions of group A MAPKKK genes. Numbers represent bootstrap scores. Names of genes used in this study are shown in boldface. Names of the three novel MAPKKK genes are underlined. B) Diagram of the domain structures of the three novel MAPKKK genes. ORFs are indicated by boxes. The 5′- and 3′-untranslated regions (UTRs) are shown as horizontal lines at the left and right, respectively, of the boxes. Shaded boxes and gray boxes indicate kinase domains and ARM domains, respectively. ORFs and UTRs are drawn to the same scale.