[Progress of study on calmodulin-binding proteins in plants].

The important Ca(2+)-sensing protein, calmodulin (CaM), plays its role in regulating cellular responses by activating specific CaM-binding proteins (CaMBPs), and therefore the study of the latter is an important way to know the mechanism of CaM and elucidate the Ca(2+)-CaM signal transduction pathway. More than fifty kinds of CaMBPs have been identified in plant kingdom. CaMBPs are distributed in all plant species and all kinds of tissues; they are involved in many biological responses during the processes of growth and development, metabolism regulation and cell division, such as responses to phytohormones, to stress, and to pathogen, and transcription activation. This review summarizes the recent progress on the interaction of CaMBPs with CaM, their distribution, their subcellular localization, and involvement in biological functions.

Characterization of a cDNA coding for an extracellular calmodulin-binding protein from suspension-cultured cells of Angelica dahurica.

In order to characterize a specific extracellular 21-kDa calmodulin-binding protein (named: ECBP21) from Angelica dahurica L. suspension-cultured cells, the cDNA coding for the protein has been cloned. Here, Southern blot analysis shows that there are at least two copies of ECBP21 gene in Angelica genome. Using truncated versions of ECBP21 and synthetic peptide in CaM binding assays, we mapped the calmodulin-binding domain to a 16-amino acid stretch (residues 200-215) at the C-terminal region. The ECBP21 was localized in the cell wall area by the immunogold electron microscopy and by GFP labeling method. These results define ECBP21 as a kind of an extracellular calmodulin-binding protein (CaMBP). Furthermore, using Northern blot analysis, we examined the expression dynamics of ecbp21 during the incubation of Angelica suspension-cultured cells and the treatments with some growth regulators. The above studies further provide the molecular evidence for the existence of the gene coding for extracellular CaMBPs and imply a possible role for ECBP21.

[Immunohistochemical analysis and immuno-gold localization of ECBP21 in Angelica dahurica].

ECBP21 is a calmodulin binding protein (CaMBP) purified from extracellular extracts of suspension-cultured cells of Angelica dahurica, and it is the first reported extracellular CaMBP in plant kingdom. We have recently cloned the full-length cDNA for ECBP21. In this work, using recombinant ECBP21 we prepared rabbit antiserum with high specificity and high titer against ECBP21, and investigated the organ-specific distribution of ECBP21 in Angelica dahurica. ECBP21 was found in all organs examined, particularly abundant in the leaves flowers, and raches, and less in the roots. It was also found in all cells examined, and particularly enriched in the cell wall. These data support the notion that ECBP21 is specifically localized extracellularly, and imply that it may be involved in plant growth and development. In addition, using immunogold transmission electron microscopy method, we studied the subcellular localization of ECBP21 in rachis cells of Angelica dahurica. The results indicated that the ECBP21 was mainly localized in cell wall; this provided a direct evidence of the extracellular existence of ECBP21.