Calmodulin as a versatile calcium signal transducer in plants

The complexity of Ca2+ patterns observed in eukaryotic cells, including pla nts, has led to the hypothesis that specific patterns of Ca2+ propagation, termed Ca2+ signatures, encode information and relay it to downstream eleme nts (effectors) for translation into appropriate cellular responses. Ca2+-b inding proteins (sensors) play a key role in decoding Ca2+-calmodulin signa tures and transducing signals by activating specific targets and pathways. Calmodulin is a Ca2+ sensor known to modulate the activity of many mammalia n proteins, whose targets in plants are now being actively characterized. P lants possess an interesting and rapidly growing list of calmodulin targets with a variety of cellular roles. Nevertheless, many targets appear to be unique to plants and remain uncharacterized, calling for a concerted effort to elucidate their functions. Moreover, the extended family of calmodulin- related proteins in plants consists of evolutionarily divergent members, mo stly of unknown function, although some have recently been implicated in st ress responses. It is hoped that advances in functional genomics, and the r esearch tools it generates, will help to explain the multiplicity of calmod ulin genes in plants, and to identify their downstream effecters. This revi ew summarizes current knowledge of the Ca2+-calmodulin messenger system in plants and presents suggestions for future areas of research.