The calmodulin-like protein CML43 functions as a salicylic-acid-inducible root-specific Ca2+ sensor in Arabidopsis

Abstract

Many signalling pathways in plants are regulated by the second messenger calcium (Ca(2+)). In the standard model, Ca(2+)-sensor proteins, such as CaM (calmodulin), detect Ca(2+) signals and subsequently regulate downstream targets to advance the signal transduction cascade. In addition to CaM, plants possess many CMLs (CaM-like proteins) that are predicted to function as Ca(2+) sensors, but which remain largely uncharacterized. In the present study, we examined the biochemical properties, subcellular localization and tissue-specific distribution of Arabidopsis CML43. Our data indicate that CML43 displays characteristics typical of Ca(2+) sensors, including high-affinity Ca(2+) binding, conformational changes upon Ca(2+) binding that expose hydrophobic regions and stabilization of structure in the presence of Mg(2+) or Ca(2+). In vivo localization analysis demonstrates that CML43 resides in cytosolic and nuclear compartments. Transgenic plants expressing a CML43:GUS (β-glucoronidase) promoter reporter gene revealed that CML43 promoter activity is restricted almost exclusively to root tips under normal growth conditions. GUS reporter activity in these transgenic plants was strongly increased when exposed to the defence compound SA (salicylic acid). Furthermore, immunoblot analysis revealed that the CML43 protein accumulates following treatment with SA. Collectively, our findings suggest that CML43 functions as a Ca(2+) sensor in root tips during both normal growth and plant immune response.

The interaction of salicylic acid and Ca2+ alleviates aluminum toxicity in soybean (Glycine max L.)

“…The expression of CML43 is up-regulated when Arabidopsis plant is treated with SA. Thus, CML43 functions as a SA-inducible, rootspecific Ca 2þ sensor in Arabidopsis (Bender et al, 2014). We found that SA enhanced the expression of four genes within 4 h under Al stress, indicating that SA can regulate gene expression to generate physiological responses for Al tolerance in soybean through Ca 2þ signaling pathway.…”

“…During an intracellular Ca 2þ signal transduction, Ca 2þ is bound to calcium-binding proteins. Ca 2þ signals can be detected by Ca 2þ sensor proteins, such as calmodulin (CaM) or CaM-like proteins (CMLs) (Bender et al, 2014).…”

CaM and CML emergence in the green lineage

“…When CML sequences were judged as incomplete, the prediction of full protein sequences (file 1 in the supplementary material online) was carried out using EXPASY tools (http://web.expasy.org/translate/) and an ab initio strategy using FGENESH (http:// www.softberry.com) for prediction of the full protein sequence (sequences are provided in file 1 in the supplementary material online). Sequence alignments were performed using Muscle with default parameters (http://www.ebi.ac.uk/ Tools/msa/muscle/) and the phylogenetic trees were generated with the Maximal Likelihood method using MEGA6 (Bootstrap 500) [ root development [29,45]. Groups IV and VI correlate with the emergence of angiosperms and to the formation of new organs, such as seeds and flowers, and this is supported by evidence showing that CML39, a CML from group VI, is essential for seedling establishment in Arabidopsis [30].…”

Metal binding affinity and structural properties of calmodulin‐like protein 14 from Arabidopsis thaliana

“…Some CMLs contain variable N‐ or C‐terminal extensions that could constitute targeting sequences for organelle sorting, or motifs for myristoylation . Growing research on CMLs functional roles has revealed their involvement in different developmental processes, as well as in the response to stresses . This information, together with the presence and diversification of CMLs across plant taxa, allowed speculation that CMLs have distinct functions and that their evolution is related to the necessity for more specialized Ca 2+ sensors in the colonization of new terrestrial environment .…”