Calmodulins and related potential calcium sensors of Arabidopsis

Abstract

Summary• Calcium (Ca 2+ ) signaling is thought to orchestrate responses to cellular stimuli. The efficacy of Ca 2+ signaling requires mediation by Ca 2+ -binding proteins.• The determination of the Arabidopsis genome sequence enables the identification of genes encoding potential Ca 2+ sensors.• Six Arabidopsis loci are defined as calmodulin ( CAM ) genes. Fifty additional genes are CAM-like ( CML ) genes, encoding proteins composed mostly of EF-hand Ca 2+ -binding motifs, have no other identifiable functional domains, and at least 16% identical with CaM. Number and structural diversity of the EF hands are evaluated. Intron/exon boundaries, phylogenetic tree and chromosomal distribution data for the CAMs and CMLs are presented.• Arabidopsis has 6 CAM genes, encoding only 3 isoforms. Maintenance of these genes suggests that they are unlikely to be fully redundant in function. Furthermore, the repeated EF hand motif is incorporated into at least 50 additional loci. The CaM relatives have altered EF hand number, organization, and predicted functional capacity. Additional structural differences and expression behaviors also indicate that the CML family has likely evolved distinct roles from the CAMs .

Arabidopsis CML38, a Calcium Sensor That Localizes to Ribonucleoprotein Complexes under Hypoxia Stress

“…Protein sequences for CaM1 to CaM7 and CML1 to CML50 were downloaded from TAIR (www.arabidopsis.org) using the accession numbers reported in (McCormack and Braam, 2003). The sequence for tobacco (Nicotiana tabacum) rgsCaM comes from GI: 12963415 (Anandalakshmi et al, 2000).…”

“…The most well characterized of these is the ubiquitous calcium sensor calmodulin (Chin and Means, 2000); however, higher plants have a large collection of calmodulin-like proteins (CMLs) that contain EF hands but have diverged from calmodulin in structure and function (McCormack and Braam, 2003;Bender and Snedden, 2013). To gain insight into the calcium sensors involved in the hypoxia-response program in Arabidopsis, the interaction targets and subcellular localization of CML38 in Arabidopsis were investigated.…”

Cloning and Characterization of Two NAD Kinases from Arabidopsis. Identification of a Calmodulin Binding Isoform

“…We examined the responsiveness of Arabidopsis native NADK to seven novel Arabidopsis CML recombinant proteins and a previously described protein, CML10 (originally termed CaBP-22; Ling and Zielinski, 1993). These CMLs were chosen because they represent a reasonable selection from across the various CML subfamilies found in Arabidopsis (McCormack and Braam, 2003). Activity was measured relative to that observed using a recombinant conserved CaM (petunia CaM81).…”

“…The standard assay mixture, unless otherwise specified, contained 50 mM Tris-Cl (pH 7.9), 4 mM ATP, 4 mM NAD, 10 mM MgCl 2 , 1 mM CaCl 2 , and 300 nM recombinant petunia CaM81 (S70768, prepared as described in Fromm and Chua, 1992). It should be noted that petunia CaM81, which is 100% identical to Arabidopsis CaM7 (P59220) and about 90% identical to human CaM (NP_001734) at the peptide sequence level, is considered an evolutionarily conserved form of CaM (McCormack and Braam, 2003) and thus served as a standard reference for CaM-dependent NADK activity throughout our analyses. The reaction was initiated with up to 18 mL of protein extract and allowed to proceed for 30 min at 25°C.…”

“…It is noteworthy that plants possess unique CaM targets not found in animals and have also evolved targets whose animal homologs are not CaM regulated (Reddy et al, 2002;Yang and Poovaiah, 2003). Moreover, plants possess not only the evolutionarily conserved form of CaM but also an extended family of CaM-like proteins (CMLs) not present in other organisms (McCormack and Braam, 2003). Physiological roles for many of these putative Ca 21 sensors remain to be established, but several show differential regulation of plant NADK (Liao et al, 1996;Lee et al, 1997).…”