Phylogenetic trees of proteasome subunits PBA and PBB (A) and phytaspases (B) drawn with the ClustalW software.

<p>The horizontal scale represents the evolutionary distance expressed as a number of substitutions per amino acid. The putative phytaspases and proteasome subunits PBA1 of barley are shown in bolt. (A) Putative barley (Hv) proteasome subunits PBA and PBB are similar to the corresponding genes from <i>Arabidopsis thaliana</i> (At), <i>Populus tomentosa</i> (Pt) and <i>Oryza sativa</i> (Os). (B) Putative barley (Hv) phytaspases together with phytaspases from <i>Nicotiana tabacum</i> (Nt) and <i>Oryza sativa</i> (Os) belong to the subgroup 1 of subtilase-like proteases. The phytaspases with proven caspase-6 activity are shown in italic. Only one Arabidopsis subtilase-like protease per subgroup is shown (Rautengarten et al., 2008) in order to simplify the figure.