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

Abstract

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.

Mechanical touch responses of Arabidopsis TCH1-3 mutant roots on inclined hard-agar surface

“…Although we did not discover the significant defective mechanoresponses behaviour of tch1 in our work, the functional redundancy of CAMs and CMLs family may remedy the defective function of the deficiency of TCH1 (Delk et al, 2005;McCormack and Braam, 2003;McCormack et al, 2005). Taken together, the normal function of the TCH 1-3 genes may be necessary for Arabidopsis primary root mechanoresponse in the present study, especially TCH2 (CML24-2 and CML24-4) and TCH3 (CML12-2), and the potential roles of CAMs and CMLs in mechano-related physiological events will also be an important future research direction.…”

CML42-Mediated Calcium Signaling Coordinates Responses to Spodoptera Herbivory and Abiotic Stresses in Arabidopsis

“…Thus, loss of function of CML42 is detrimental for plant resistance to UV-B stress. It is known that CMLs control many abiotic stress response pathways, and some act as regulators of ABA biosynthesis (Delk et al, 2005;Hubbard et al, 2008). Therefore, we looked for the impact of drought stress on the wild type and cml42.…”

“…CML37, -38, and -39 transcripts are regulated by biotic and abiotic stress as well as hormone and chemical treatment (Vanderbeld and Snedden, 2007). CML24 is known to cause alterations in flowering time, abscisic acid (ABA), and ion stress (Delk et al, 2005;Hubbard et al, 2008). CML9 alters plant responses to ABA and abiotic stress (Magnan et al, 2008), and loss of CML42 function leads to aberrant trichomes with increased branching (Dobney et al, 2009).…”

Calmodulin-like protein CML37 is a positive regulator of ABA during drought stress in Arabidopsis

“…For instance, CML24 can cause changes in abscisic acid (ABA) level during ion stress as well as changes in flowering time; it also regulates pollen tube growth by modulating the actin cytoskeleton and controlling the cytosolic Ca 2C concentration. [5][6][7] CML39 functions during early seedling establishment and activates defense responses.…”