| Summary: | <p>Abstract</p> <p>Background</p> <p>FK506 binding proteins (FKBPs) and cyclophilins (CYPs) are abundant and ubiquitous proteins belonging to the peptidyl-prolyl <it>cis/trans </it>isomerase (PPIase) superfamily, which regulate much of metabolism through a chaperone or an isomerization of proline residues during protein folding. They are collectively referred to as immunophilin (IMM), being present in almost all cellular organs. In particular, a number of IMMs relate to environmental stresses.</p> <p>Results</p> <p>FKBP and CYP proteins in rice (<it>Oryza sativa </it>cv. Japonica) were identified and classified, and given the appropriate name for each IMM, considering the ortholog-relation with <it>Arabidopsis </it>and <it>Chlamydomonas </it>or molecular weight of the proteins. 29 FKBP and 27 CYP genes can putatively be identified in rice; among them, a number of genes can be putatively classified as orthologs of <it>Arabidopsis </it>IMMs. However, some genes were novel, did not match with those of <it>Arabidopsis </it>and <it>Chlamydomonas</it>, and several genes were paralogs by genetic duplication. Among 56 IMMs in rice, a significant number are regulated by salt and/or desiccation stress. In addition, their expression levels responding to the water-stress have been analyzed in different tissues, and some subcellular IMMs located by means of tagging with GFP protein.</p> <p>Conclusion</p> <p>Like other green photosynthetic organisms such as <it>Arabidopsis </it>(23 FKBPs and 29 CYPs) and <it>Chlamydomonas </it>(23 FKBs and 26 CYNs), rice has the highest number of IMM genes among organisms reported so far, suggesting that the numbers relate closely to photosynthesis. Classification of the putative FKBPs and CYPs in rice provides the information about their evolutional/functional significance when comparisons are drawn with the relatively well studied genera, <it>Arabidopsis </it>and <it>Chlamydomonas</it>. In addition, many of the genes upregulated by water stress offer the possibility of manipulating the stress responses in rice.</p>
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