Editing Calmodulin (section)

==  Role in plants ==
{{Unreferenced section|date=March 2020}}
[[File:Sorghum bicolor (4171536532).jpg|right|thumb|[[Sorghum]] plant contains temperature-responsive genes. These [[genes]] help the plant [[Adaptation|adapt]] in extreme weather conditions such as hot and dry [[Natural environment|environment]]s.]]
While yeasts have only a single CaM gene, plants and vertebrates contain an evolutionarily conserved form of CaM genes. The difference between plants and animals in Ca<sup>2+</sup> signaling is that the plants contain an extended family of the CaM in addition to the evolutionarily conserved form.<ref>{{cite journal | vauthors = Ranty B, Aldon D, Galaud JP | title = Plant calmodulins and calmodulin-related proteins: multifaceted relays to decode calcium signals | journal = Plant Signaling & Behavior | volume = 1 | issue = 3 | pages = 96–104 | date = May 2006 | pmid = 19521489 | pmc = 2635005 | doi = 10.4161/psb.1.3.2998 }}</ref> Calmodulins play an essential role in plant development and adaptation to environmental stimuli.

Calcium plays a key role in the structural integrity of the cell wall and the membrane system of the cell. However, high calcium levels can be toxic to a plant's cellular energy metabolism and, hence, the Ca<sup>2+</sup> concentration in the cytosol is maintained at a submicromolar level by removing the cytosolic Ca<sup>2+</sup> to either the [[apoplast]] or the lumen of the intracellular organelles. Ca<sup>2+</sup> pulses created due to increased influx and efflux act as cellular signals in response to external stimuli such as hormones, light, gravity, abiotic stress factors and also interactions with pathogens.<ref>{{Cite journal |last1=Virdi |first1=Amardeep S. |last2=Singh |first2=Supreet |last3=Singh |first3=Prabhjeet |date=2015 |title=Abiotic stress responses in plants: roles of calmodulin-regulated proteins |journal=Frontiers in Plant Science |volume=6 |page=809 |doi=10.3389/fpls.2015.00809 |pmid=26528296 |pmc=4604306 |issn=1664-462X|doi-access=free }}</ref>

=== CMLs (CaM-related proteins) ===
Plants contain CaM-related proteins (CMLs) apart from the typical CaM proteins. The CMLs have about 15% amino acid similarity with the typical CaMs. ''[[Arabidopsis thaliana]]'' contains about 50 different CML genes,<ref>{{Cite journal |last1=Yang |first1=Dong |last2=Chen |first2=Ting |last3=Wu |first3=Yushuang |last4=Tang |first4=Huiquan |last5=Yu |first5=Junyi |last6=Dai |first6=Xiaoqiu |last7=Zheng |first7=Yixiong |last8=Wan |first8=Xiaorong |last9=Yang |first9=Yong |last10=Tan |first10=Xiaodan |date=2024-02-21 |title=Genome-wide analysis of the peanut CaM/CML gene family reveals that the AhCML69 gene is associated with resistance to Ralstonia solanacearum |journal=BMC Genomics |volume=25 |issue=1 |pages=200 |doi=10.1186/s12864-024-10108-5 |doi-access=free |issn=1471-2164 |pmc=10880322 |pmid=38378471}}</ref> which leads to the question of what purpose these diverse ranges of proteins serve in the cellular function. All plant species exhibit this diversity in the CML genes. The different CaMs and CMLs differ in their affinity to bind and activate the CaM-regulated enzymes ''in vivo''. The CaM or CMLs are also found to be located in different organelle compartments.

===Plant growth and development===
In ''Arabidopsis,'' the protein [[DWF1]] plays an enzymatic role in the biosynthesis of brassinosteroids, steroid hormones in plants that are required for growth. An interaction occurs between CaM and DWF1,{{Clarify|reason="An interaction" is not specific enough|date=March 2020}} and DWF1 being unable to bind CaM is unable to produce a regular growth phenotype in plants. Hence, CaM is essential for the DWF1 function in plant growth.

CaM binding proteins are also known to regulate reproductive development in plants. For instance, the CaM-binding protein kinase in tobacco acts as a negative regulator of flowering. However, these CaM-binding protein kinase are also present in the shoot [[Apical Meristem|apical meristem]] of tobacco and a high concentration of these kinases in the meristem causes a delayed transition to flowering in the plant.

''S''-locus receptor kinase (SRK) is another protein kinase that interacts with CaM. SRK is involved in the self-incompatibility responses involved in pollen-pistil interactions in ''[[Brassica]]''.

CaM targets in ''Arabidopsis'' are also involved in pollen development and fertilization. Ca<sup>2+</sup> transporters are essential for [[pollen tube]] growth. Hence, a constant Ca<sup>2+</sup> gradient is maintained at the apex of pollen tube for elongation during the process of fertilization. Similarly, CaM is also essential at the pollen tube apex, where its primarily role involves the guidance of the pollen tube growth.

===Interaction with microbes===
====Nodule formation====
Ca<sup>2+</sup> plays an important role in nodule formation in legumes. Nitrogen is an essential element required in plants and many legumes, unable to fix nitrogen independently, pair symbiotically with nitrogen-fixing bacteria that reduce nitrogen to ammonia. This legume-''[[Rhizobium]]'' interaction establishment requires the Nod factor that is produced by the ''Rhizobium'' bacteria. The [[Nod factor]] is recognized by the root hair cells that are involved in the nodule formation in legumes. Ca<sup>2+</sup> responses of varied nature are characterized to be involved in the Nod factor recognition. There is a Ca<sup>2+</sup> flux at the tip of the root hair initially followed by repetitive oscillation of Ca<sup>2+</sup> in the cytosol and also Ca<sup>2+</sup> spike occurs around the nucleus. DMI3, an essential gene for Nod factor signaling functions downstream of the Ca<sup>2+</sup> spiking signature, might be recognizing the Ca<sup>2+</sup> signature. Further, several CaM and CML genes in ''[[Medicago]]'' and ''Lotus'' are expressed in nodules.

====Pathogen defense====
Among the diverse range of defense strategies plants utilize against pathogens, Ca<sup>2+</sup> signaling is very common. Free Ca<sup>2+</sup> levels in the cytoplasm increases in response to a pathogenic infection. Ca<sup>2+</sup> signatures of this nature usually activate the plant defense system by inducing defense-related genes and the hypersensitive cell death. CaMs, CMLs and CaM-binding proteins are some of the recently identified elements of the plant defense signaling pathways. Several CML genes in [[tobacco]], bean and tomato are responsive to pathogens. CML43 is a CaM-related protein that, as isolated from APR134 gene in the disease-resistant leaves of ''Arabidopsis'' for gene expression analysis, is rapidly induced when the leaves are inoculated with ''[[Pseudomonas syringae]]''. These genes are also found in tomatoes (''Solanum lycopersicum''). The CML43 from the APR134 also binds to Ca<sup>2+</sup> ions in vitro which shows that CML43 and APR134 are, hence, involved in the Ca<sup>2+</sup>-dependent signaling during the plant immune response to bacterial pathogens.<ref>{{cite journal | vauthors = Chiasson D, Ekengren SK, Martin GB, Dobney SL, Snedden WA | s2cid = 1572549 | title = Calmodulin-like proteins from Arabidopsis and tomato are involved in host defense against Pseudomonas syringae pv. tomato | journal = Plant Molecular Biology | volume = 58 | issue = 6 | pages = 887–897 | date = August 2005 | pmid = 16240180 | doi = 10.1007/s11103-005-8395-x }}</ref> The CML9 expression in ''Arabidopsis thaliana'' is rapidly induced by phytopathogenic bacteria, [[flagellin]] and salicylic acid.<ref>{{cite journal | vauthors = Leba LJ, Cheval C, Ortiz-Martín I, Ranty B, Beuzón CR, Galaud JP, Aldon D | title = CML9, an Arabidopsis calmodulin-like protein, contributes to plant innate immunity through a flagellin-dependent signalling pathway | journal = The Plant Journal | volume = 71 | issue = 6 | pages = 976–89 | date = September 2012 | pmid = 22563930 | doi = 10.1111/j.1365-313x.2012.05045.x | doi-access = free }}</ref> Expression of soybean SCaM4 and SCaM5 in transgenic ''tobacco'' and ''Arabidopsis'' causes an activation of genes related to pathogen resistance and also results in enhanced resistance to a wide spectrum of pathogen infection. The same is not true for soybean SCaM1 and SCaM2 that are highly conserved CaM isoforms. The ''At''BAG6 protein is a CaM-binding protein that binds to CaM only in the absence of Ca<sup>2+</sup> and not in the presence of it. ''At''BAG6 is responsible for the hypersensitive response of programmed cell death in order to prevent the spread of pathogen infection or to restrict pathogen growth. Mutations in the CaM binding proteins can lead to severe effects on the defense response of the plants towards pathogen infections. Cyclic nucleotide-gated channels (CNGCs) are functional protein channels in the plasma membrane that have overlapping CaM binding sites transport divalent cations such as Ca<sup>2+</sup>. However, the exact role of the positioning of the CNGCs in this pathway for plant defense is still unclear.

=== Abiotic stress response in plants ===
Change in intracellular Ca<sup>2+</sup> levels is used as a signature for diverse responses towards mechanical stimuli, osmotic and salt treatments, and cold and heat shocks. Different root cell types show a different Ca<sup>2+</sup> response to osmotic and salt stresses and this implies the cellular specificities of Ca<sup>2+</sup> patterns. In response to external stress CaM activates glutamate decarboxylase (GAD) that catalyzes the conversion of {{sc|L}}-glutamate to GABA. A tight control on the GABA synthesis is important for plant development and, hence, increased GABA levels can essentially affect plant development. Therefore, external stress can affect plant growth and development and CaM are involved in that pathway controlling this effect.{{citation needed|date=October 2017}}

===Plant examples===
====Sorghum====
The plant [[sorghum]] is well established model organism and can adapt in hot and dry environments. For this reason, it is used as a model to study calmodulin's role in plants.<ref name="Sanchez_2002" /> Sorghum contains seedlings that express a [[glycine]]-rich [[RNA-binding protein]], SbGRBP. This particular protein can be modulated by using heat as a stressor. Its unique location in the cell nucleus and cytosol demonstrates interaction with calmodulin that requires the use of Ca<sup>2+</sup>.<ref>{{cite journal | vauthors = Singh S, Virdi AS, Jaswal R, Chawla M, Kapoor S, Mohapatra SB, Manoj N, Pareek A, Kumar S, Singh P | display-authors = 6 | title = A temperature-responsive gene in sorghum encodes a glycine-rich protein that interacts with calmodulin | journal = Biochimie | volume = 137 | issue = Supplement C | pages = 115–123 | date = June 2017 | pmid = 28322928 | doi = 10.1016/j.biochi.2017.03.010 }}</ref> By exposing the plant to versatile [[stress (biology)|stress]] conditions, it can cause different [[proteins]] that enable the plant cells to tolerate environmental changes to become repressed. These modulated stress proteins are shown to interact with CaM. The ''CaMBP'' genes [[Gene expression|expressed]] in the sorghum are depicted as a “model crop” for researching the tolerance to heat and [[drought stress]].

====''Arabidopsis''====
In an ''Arabidopsis thaliana'' study, hundreds of different proteins demonstrated the possibility to bind to CaM in plants.<ref name="Sanchez_2002">{{cite journal | vauthors = Sanchez AC, Subudhi PK, Rosenow DT, Nguyen HT | s2cid = 25834614 | title = Mapping QTLs associated with drought resistance in sorghum (Sorghum bicolor L. Moench) | journal = Plant Molecular Biology | volume = 48 | issue = 5–6 | pages = 713–26 | date = 2002 | pmid = 11999845 | doi = 10.1023/a:1014894130270 }}</ref>