CML24, regulated in expression by diverse stimuli, encodes a potential Ca2+ sensor that functions in responses to abscisic acid, daylength, and ion stress.
Changes in intracellular calcium (Ca(2+)) levels serve to signal responses to diverse stimuli. Ca(2+) signals are likely perceived through proteins that bind Ca(2+), undergo conformation changes following Ca(2+) binding, and interact with target proteins. The 50-member calmodulin-like (CML) Arabidopsis (Arabidopsis thaliana) family encodes proteins containing the predicted Ca(2+)-binding EF-hand motif. The functions of virtually all these proteins are unknown. CML24, also known as TCH2, shares over 40% amino acid sequence identity with calmodulin, has four EF hands, and undergoes Ca(2+)-dependent changes in hydrophobic interaction chromatography and migration rate through denaturing gel electrophoresis, indicating that CML24 binds Ca(2+) and, as a consequence, undergoes conformational changes. CML24 expression occurs in all major organs, and transcript levels are increased from 2- to 15-fold in plants subjected to touch, darkness, heat, cold, hydrogen peroxide, abscisic acid (ABA), and indole-3-acetic acid. However, CML24 protein accumulation changes were not detectable. The putative CML24 regulatory region confers reporter expression at sites of predicted mechanical stress; in regions undergoing growth; in vascular tissues and various floral organs; and in stomata, trichomes, and hydathodes. CML24-underexpressing transgenics are resistant to ABA inhibition of germination and seedling growth, are defective in long-day induction of flowering, and have enhanced tolerance to CoCl(2), molybdic acid, ZnSO(4), and MgCl(2). MgCl(2) tolerance is not due to reduced uptake or to elevated Ca(2+) accumulation. Together, these data present evidence that CML24, a gene expressed in diverse organs and responsive to diverse stimuli, encodes a potential Ca(2+) sensor that may function to enable responses to ABA, daylength, and presence of various salts.
Delk
Nikkí A
NA
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA.
Johnson
Keith A
KA
Chowdhury
Naweed I
NI
Braam
Janet
J
D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018525:Germination / Q000187:drug effects; D017136:Ion Transport; D008027:Light; D008969:Molecular Sequence Data; D009997:Osmotic Pressure; D017440:Photoperiod; D030821:Plants, Genetically Modified; D036226:Seedlings / Q000009:adverse effects / Q000254:growth & development; D012639:Seeds / Q000187:drug effects / Q000254:growth & development; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D002135:Calcium-Binding Proteins; D002147:Calmodulin; C106145:TCH2 protein, Arabidopsis; D000040:Abscisic Acid; D002118:Calcium