ABSTRACT
Plants can sense and respond to mechanical stimuli, like animals. An early mechanism of mechanosensing and response is speculated to be governed by as-yet-unidentified sensory complexes containing a Ca(2+)-permeable, stretch-activated (SA) channel. However, the components or regulators of such complexes are poorly understood at the molecular level in plants. Here, we report the molecular identification of a plasma membrane protein (designated Mca1) that correlates Ca(2+) influx with mechanosensing in Arabidopsis thaliana. MCA1 cDNA was cloned by the functional complementation of lethality of a yeast mid1 mutant lacking a putative Ca(2+)-permeable SA channel component. Mca1 was localized to the yeast plasma membrane as an integral membrane protein and mediated Ca(2+) influx. Mca1 also increased [Ca(2+)](cyt) upon plasma membrane distortion in Arabidopsis. The growth of MCA1-overexpressing plants was impaired in a high-calcium but not a low-calcium medium. The primary roots of mca1-null plants failed to penetrate a harder agar medium from a softer one. These observations demonstrate that Mca1 plays a crucial role in a Ca(2+)-permeable SA channel system that leads to mechanosensing in Arabidopsis. We anticipate our findings to be a starting point for a deeper understanding of the molecular mechanisms of mechanotransduction in plants.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis/genetics , Calcium Channels/genetics , Membrane Proteins/genetics , Plant Roots/metabolism , Amino Acid Sequence , Arabidopsis/metabolism , Arabidopsis Proteins/metabolism , Base Sequence , Blotting, Northern , Calcium/metabolism , Cloning, Molecular , Gene Components , Genetic Complementation Test , Membrane Proteins/metabolism , Microscopy, Fluorescence , Molecular Sequence Data , Plant Roots/genetics , Sequence Analysis, DNAABSTRACT
Mechanosensitive ion channels are expected to play important roles in transducing mechanical stimuli into intracellular signals during the development and morphogenesis of higher plants. We have identified a novel mechanosensitive anion channel in the protoplast of Arabidopsis thaliana mesophyll cells by using the patch-clamp technique. The channel in the outside-out patches could be activated by positive pressure in the pipette while negative pressure had no effect. The amphipathic membrane crenator trinitrophenol, which is supposed to preferentially insert in the outer leaflet of the lipid bilayer of the plasma membrane, synergized with mechanical membrane stretch to activate the channel. These results suggest that the channel activation is mediated by a convex curvature of the plasma membrane. Therefore, activation of this channel may play an important role when cell volume is increasing during cell growth or hypo-osmotic challenge, which is accompanied by membrane stretch with increasingly convex curvature.
Subject(s)
Anions/metabolism , Arabidopsis/metabolism , Ion Channels , Patch-Clamp Techniques , Protoplasts/metabolismSubject(s)
Calcium Channels/physiology , Calcium Signaling/genetics , Calcium/metabolism , Plant Physiological Phenomena , Plants/metabolism , Arabidopsis Proteins/physiology , Calcium Signaling/physiology , Cyclic Nucleotide-Gated Cation Channels , Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels , Ion Channels/physiology , Mechanoreceptors/physiology , Plants/genetics , Potassium Channels , Receptors, Neurotransmitter/physiologyABSTRACT
Theoretical studies by computer simulation have shown that vibrational modes, which depend on the subdomain motions of proteins, are located in the submillimeter wave region (i.e., 10-100 cm(-1)], 0.3-3 THz). We have successfully observed, by measuring the difference spectrum between squid rhodopsin and metarhodopsin to avoid water absorption, that squid rhodopsin shows its absorption features in this region. Our experimental results show that a native protein in solution indicates not only an absorbent property in this region but also an actual change of absorption with changes in protein conformation.
