Evolutionary relationship of Populus MIPs. Phylogenetic analysis of all Populus MIPs is shown along with MIPs from Arabidopsis. Neighbor-Joining (NJ) method was used to create this unrooted tree. NJ method used the multiple sequence alignment generated by T-COFFEE to generate the tree. Populus MIP subfamilies PtPIPs, PtTIPs, PtNIPs and PtSIPs clustered with the corresponding Arabidopsis MIP subfamilies. XIPs observed only in Populus clearly form a separate group. Each MIP subfamily is shown with a specific background color to distinguish them from others. A similar result is obtained when the same analysis was carried out with rice and maize MIPs (Additional files 2 to 4).