Homology trees of PMEI, PME2, and PME31. Multiple-sequence alignments were performed using ClustalW, and neighbor-joining trees were built using MEGA5.1. The GenBank accession numbers are listed next to gene names; GhPMEI3, GhPME2, and GhPME31 from this study are framed by red boxes. The numbers at nodes represent the branch support values.