title: The Arabidopsis calmodulin-like protein, CML39, functions during early seedling establishment.
abstract: During Ca(2+) signal transduction, Ca(2+)-binding proteins known as Ca(2+) sensors function to decode stimulus-specific Ca(2+) signals into downstream responses. Plants possess extended families of unique Ca(2+) sensors termed calmodulin-like proteins (CMLs) whose cellular roles are not well understood. CML39 encodes a predicted Ca(2+) sensor whose expression is strongly increased in response to diverse external stimuli. In the present study, we explored the biochemical properties of recombinant CML39, and used a reverse genetics approach to investigate its physiological role. Our data indicate that Ca(2+) binding by CML39 induces a conformational change in the protein that results in an increase in exposed-surface hydrophobicity, a property that is consistent with its predicted function as a Ca(2+) sensor. Loss-of-function cml39 mutants resemble wild-type plants under normal growth conditions but exhibit persistent arrest at the seedling stage if grown in the absence of sucrose or other metabolizable carbon sources. Under short-day conditions, cml39 mutants display increased sucrose-induced hypocotyl elongation. When grown in the dark, cml39 mutants show impaired hypocotyl elongation in the absence of sucrose. Promoter-reporter data indicate that CML39 expression is prominent in the apical hook in dark-grown seedlings. Collectively, our data suggest that CML39 functions in Arabidopsis as a Ca(2+) sensor that plays an important role in the transduction of light signals that promote seedling establishment.
authors.affiliation: Department of Biology, Queen's University, Kingston, ON, K7L 3N6, Canada.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Bender
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Rosenbaum
authors.forename: Barbara
authors.initials: B
authors.lastname: Vanderbeld
authors.forename: Midhat
authors.initials: M
authors.lastname: Ubaid
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Snedden
mesh_terms: D017360:Arabidopsis / Q000502:physiology* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D002147:Calmodulin / Q000502:physiology*; D002736:Chloroplasts / Q000648:ultrastructure; D008027:Light; D036226:Seedlings / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C522737:CML39 protein, Arabidopsis; D002147:Calmodulin; D013395:Sucrose; D013213:Starch
keywords: CML39; Ca2+ sensor; Ca2+ signalling; development; seedling establishment; sucrose