CML24, Regulated in Expression by Diverse Stimuli, Encodes a Potential Ca²⁺ Sensor That Functions in Responses to Abscisic Acid, Daylength, and Ion Stress

• Published in: Plant physiology (Bethesda) Vol. 139; no. 1; pp. 240 - 253
• Main Authors: Delk, Nikkí A, Johnson, Keith A, Chowdhury, Naweed I, Braam, Janet
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.09.2005; American Society of Plant Physiologists
• Subjects: abiotic stress; abscisic acid; Abscisic Acid - pharmacology; Amino Acid Sequence; amino acid sequences; Antibodies; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Biological and medical sciences; Calcium; Calcium - metabolism; calcium-binding proteins; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Calmodulin; calmodulin-related proteins; cations; Cell physiology; Environmental Stress and Adaptation; ethylene; Flowering; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Gene expression regulation; Gene Expression Regulation, Developmental - drug effects; Gene Expression Regulation, Plant - drug effects; Germination - drug effects; gibberellic acid; indole acetic acid; Ion Transport; Light; magnesium; messenger RNA; Molecular Sequence Data; nucleotide sequences; Osmotic Pressure; Photoperiod; plant biochemistry; plant ecology; plant genetics; Plant physiology and development; plant proteins; plant stress; Plants; Plants, Genetically Modified; Plasma membrane and permeation; RNA; seed germination; seedling growth; Seedlings; Seedlings - adverse effects; Seedlings - growth & development; Seeds - drug effects; Seeds - growth & development; Sensors; Sequence Homology, Amino Acid; signal transduction; tissue distribution; Transgenic plants; Cold; Growth; Germination; Tolerance; Stomata; Trichome; Stress; Salinity; Arabidopsis thaliana; Gene; Cruciferae; Mechanical stress; Dicotyledones; Angiospermae; Abscisic acid; Flowering; Spermatophyta; Inhibition; Calmodulin; Aminoacid sequence
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.105.062612

Changes in intracellular calcium (Ca²⁺) levels serve to signal responses to diverse stimuli. Ca²⁺ signals are likely perceived through proteins that bind Ca²⁺, undergo conformation changes following Ca²⁺ binding, and interact with target proteins. The 50-member calmodulin-like (CML) Arabidopsis (Arabidopsis thaliana) family encodes proteins containing the predicted Ca²⁺-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 Ca²⁺-dependent changes in hydrophobic interaction chromatography and migration rate through denaturing gel electrophoresis, indicating that CML24 binds Ca²⁺ 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 CoCl₂, molybdic acid, ZnSO₄, and MgCl₂. MgCl₂ tolerance is not due to reduced uptake or to elevated Ca²⁺ accumulation. Together, these data present evidence that CML24, a gene expressed in diverse organs and responsive to diverse stimuli, encodes a potential Ca²⁺ sensor that may function to enable responses to ABA, daylength, and presence of various salts.