Unrooted phylogenetic tree of the WRKY domains. The tree was reconstructed from the amino acid sequences using the neighbor-joining program from Phylip 3.57. Clades of WRKY domains are labelled according to the classifications of AtWRKY domains by Eulgem et al  who proposed three groups and five subgroups in Group 2 (a, b, c, d and e). We suggest classifying WRKY domains into five groups modified from the old system. While Groups 1 and 3 are unchanged, the original subgroup 2_c is promoted to Group 2_c. Subgroups 2_a and 2_b, and subgroups 2_d and 2_e are combined to form two new groups, 2_a + 2_b, and 2_d + 2_e, respectively (see text for details). WRKY domains from G. lamblia are represented by thick and dark-green branches; the slime mold, thick and cyan; the green alga, thick and magenta; Arabidopsis, thin and blue; and rice, thin and red.