Expression of group B and C MPK genes has also been investigated in other species. For example, the phylogenetically closely related Arabidopsis AtMPK1 and AtMPK2, as well as the Petunia hybrida PhMEK1 gene and the tobacco Ntf3 gene, showed constitutive expression in various organs (leaves, stem, roots and flowers) [37,43,60]. Interestingly, AtMPK2 is more highly expressed than AtMPK1 in the analyzed organs [60], a situation also observed for the poplar predicted ortholog PtMPK1 over PtMPK2.