Analysis of the pattern of exon-intron junctions can provide important insights into the evolution of gene families. Therefore, we extracted data regarding predicted exon and intron distribution for the coding regions of all PtMPKs and PtMKKs (Figures 3 and 4) as well as for all Arabidopsis putative orthologs (AtMPKs, Figure 5 and AtMKKs, Figure 6). Group A PtMPKs exhibit a highly conserved distribution of exons and introns (Figure 3) consisting of six exons of conserved length, and five introns of conserved or variable sizes. PtMPKs belonging to group B also possess six exons, with lengths similar to those found in group A PtMPKs, while the associated introns vary in size between the different members of group B. Group C PtMPKs are each composed of only two exons with strictly conserved or very similar sizes. PtMPK14 is the only group C member with a shorter intron (398 vs ~ 1200 base pairs for the other three members).