title: Phosphorylation of S344 in the calmodulin-binding domain negatively affects CCaMK function during bacterial and fungal symbioses.
abstract: Calcium and Ca(2+)/calmodulin-dependent protein kinase (CCaMK) plays a critical role in the signaling pathway that establishes root nodule symbiosis and arbuscular mycorrhizal symbiosis. Calcium-dependent autophosphorylation is central to the regulation of CCaMK, and this has been shown to promote calmodulin binding. Here, we report a regulatory mechanism of Medicago truncatula CCaMK (MtCCaMK) through autophosphorylation of S344 in the calmodulin-binding/autoinhibitory domain. The phospho-ablative mutation S344A did not have significant effect on its kinase activities, and supports root nodule symbiosis and arbuscular mycorrhizal symbiosis, indicating that phosphorylation at this position is not required for establishment of symbioses. The phospho-mimic mutation S344D show drastically reduced calmodulin-stimulated substrate phosphorylation, and this coincides with a compromised interaction with calmodulin and its interacting partner, IPD3. Functional complementation tests revealed that the S344D mutation blocked root nodule symbiosis and reduced the mycorrhizal association. Furthermore, S344D was shown to suppress the spontaneous nodulation associated with a gain-of-function mutant of MtCCaMK (T271A), revealing that phosphorylation at S344 of MtCCaMK is adequate for shutting down its activity, and is epistatic over previously identified T271 autophosphorylation. These results reveal a mechanism that enables CCaMK to 'turn off' its function through autophosphorylation.
authors.affiliation: Graduate Program in Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-6414, USA; Department of Horticulture, Washington State University, Pullman, WA, 99164-6414, USA.
authors.forename: Pratyush
authors.initials: P
authors.lastname: Routray
authors.forename: J Benjamin
authors.initials: JB
authors.lastname: Miller
authors.forename: Liqun
authors.initials: L
authors.lastname: Du
authors.forename: Giles
authors.initials: G
authors.lastname: Oldroyd
authors.forename: B W
authors.initials: BW
authors.lastname: Poovaiah
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000502:physiology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology; D005816:Genetic Complementation Test; D046913:Medicago truncatula / Q000235:genetics / Q000382:microbiology / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D038821:Mycorrhizae / Q000502:physiology; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D055170:Plant Root Nodulation / Q000502:physiology; D012231:Rhizobium / Q000502:physiology; D015398:Signal Transduction; D013559:Symbiosis
chemical_list: D002147:Calmodulin; D010940:Plant Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium
keywords: Medicago truncatula; arbuscular mycorrhizal symbiosis; autophosphorylation; calcium and Ca2+/calmodulin-dependent protein kinase; calcium signaling; calmodulin-binding domain; protein kinase; root nodule symbiosis