Phylogenetic tree of plant hexokinases. The sequences included in the comparison were those predicted by the ten hexokinase-encoding genes in the rice genome, the six hexokinase and hexokinase-like genes in the Arabidopsis genome and the eleven Physcomitrella hexokinases discussed in the present work. Aligned amino acid sequences corresponding to residues 69-439 in PpHxk1, which excludes the divergent N- and C-termini, were used to calculate a phylogenetic tree as described in Methods. The alignment is shown in additional file 5: Figure S1. Hexokinase sequences from the budding yeast S. cerevisiae (ScHxk2), the fission yeast S. pombe, the nematode C. elegans, and human glucokinase (hexokinase IV) were included to root the tree. The subdivisions of the hexokinases into types A, B, C and D and their intracellular localisation, if known, are also shown. BX stands for seed plant proteins that cluster with the type B hexokinases, but whose N-termini are less conserved. The bar represents a PAM value (percent accepted point mutations) of 10%. The numbers at the branch points are bootstrap values derived from 1000 randomized sequences.