Phylogenetic tree showing the relationships between the deduced amino acid sequences of PDI and PDI-like genes of different plant species. The multiple alignment of nine sequences of wheat, 13 of A. thaliana (At), 12 of P. trichocarpa (Pt), 10 of V. vinifera (Vv), 21 of G. max (Gm), 12 each of Z. mais (Zm) and O. sativa (Os) and 14 of P. patens (Pp) was performed by ClustalX 1.83 software and the phylogenetic tree was constructed by the neighbour-joining (NJ) method and evaluated by bootstrap analysis (PHYLIP version 3.6). The numbers on the main branches indicate bootstrap percentages for 1,000 replicates. The PDI-like sequences of groups VI and VIII were used as outgroups, due to their high diversification from the other subfamilies. The two major clades (I and II) and the eight phylogenetic groups (I-VIII) indentified in the plant PDI family are highlighted with red and green brackets, respectively.