Analysis of EF-hand-containing proteins in Arabidopsis

BACKGROUND: In plants, calcium (Ca(2+)) has emerged as an important messenger mediating the action of many hormonal and environmental signals, including biotic and abiotic stresses. Many different signals raise cytosolic calcium concentration ([Ca(2+)](cyt)), which in turn is thought to regulate cellular and developmental processes via Ca(2+)-binding proteins. Three out of the four classes of Ca(2+)-binding proteins in plants contain Ca(2+)-binding EF-hand motif(s). This motif is a conserved helix-loop-helix structure that can bind a single Ca(2+) ion. To identify all EF-hand-containing proteins in Arabidopsis, we analyzed its completed genome sequence for genes encoding EF-hand-containing proteins. RESULTS: A maximum of 250 proteins possibly having EF-hands were identified. Diverse proteins, including enzymes, proteins involved in transcription and translation, protein- and nucleic-acid-binding proteins and a large number of unknown proteins, have one or more putative EF-hands. Phylogenetic analysis identified six major groups that contain some families of proteins. CONCLUSIONS: The presence of EF-hand motif(s) in a diversity of proteins is consistent with the involvement of Ca(2+) in regulating many cellular and developmental processes. Thus far, only 47 of the possible 250 EF-hand proteins have been reported in the literature. Various domains that we identified in many of the uncharacterized EF-hand-containing proteins should help in elucidating their cellular role(s). Our analyses suggest that the Ca(2+) messenger system is widely used in plants and that EF-hand-containing proteins are likely to be the key transducers mediating Ca(2+) action.