Model of the origin and duplications of WRKY gene family. The phylogenetic tree of eukaryotes using the archaea as the outgroup is modified from Baldauf and Doolittle  and Kenrick and Crane . The solid lines correspond to branches where WRKY homologues are identified, while the thickness of the line represents the relative size of WRKY family for the branch, from the thinnest for one copy in Giardia, the slime mold and the green alga to the thickest for over 100 copies in rice. The broken lines represent branches where WRKY genes are not present or have not been identified. The WRKY gene is symbolized by the box for the WRKY domain and the lines for sequences around the domain. The text in the box indicates the group the WRKY domain belongs to (1, Group 1; 1N and 1C, N- and C-terminal domains of Group 1 proteins; a + b: Group 2_a + 2_b; c: Group 2_c; d + e, Group 2_d + 2_e; 3: Group 3). The major gene duplications and diversifications are shown above the branch. The number shown below the branch is the divergence time (million years ago) of its children branches. The branch length is not scaled to the evolutionary distance.