Figure 2.

Phylogenetic analysis of the Arabidopsis expansin gene family shows three major groups: α, β, and γ. The composite tree was derived by neighbor-joining distance analysis using ClustalX version 1.8. The main backbone of the tree was calculated with the 90-residue conserved core of amino acid positions alignable among all 38 sequences. The three subtrees were then calculated separately based on additional amino acid positions shared within each group, and were appended to the main backbone tree as indicated by broken horizontal lines. Only bootstrap values over 60% are indicated above the nodes. The major expansin subfamilies α, β, and γ are highlighted by shaded boxes. Hypothetical intron gains and losses are indicated by diamonds followed by intron number. Postulated intron gains are indicated by filled diamonds, and intron losses are indicated by unfilled diamonds. All branches are drawn to scale as indicated by the scale bar (=0.1 substitutions/site).