title: Rapid hyperosmotic-induced Ca2+ responses in Arabidopsis thaliana exhibit sensory potentiation and involvement of plastidial KEA transporters.
abstract: Plants experience hyperosmotic stress when faced with saline soils and possibly with drought stress, but it is currently unclear how plant roots perceive this stress in an environment of dynamic water availabilities. Hyperosmotic stress induces a rapid rise in intracellular Ca(2+) concentrations ([Ca(2+)]i) in plants, and this Ca(2+) response may reflect the activities of osmo-sensory components. Here, we find in the reference plant Arabidopsis thaliana that the rapid hyperosmotic-induced Ca(2+) response exhibited enhanced response magnitudes after preexposure to an intermediate hyperosmotic stress. We term this phenomenon "osmo-sensory potentiation." The initial sensing and potentiation occurred in intact plants as well as in roots. Having established a quantitative understanding of wild-type responses, we investigated effects of pharmacological inhibitors and candidate channel/transporter mutants. Quintuple mechano-sensitive channels of small conductance-like (MSL) plasma membrane-targeted channel mutants as well as double mid1-complementing activity (MCA) channel mutants did not affect the response. Interestingly, however, double mutations in the plastid K(+) exchange antiporter (KEA) transporters kea1kea2 and a single mutation that does not visibly affect chloroplast structure, kea3, impaired the rapid hyperosmotic-induced Ca(2+) responses. These mutations did not significantly affect sensory potentiation of the response. These findings suggest that plastids may play an important role in early steps mediating the response to hyperosmotic stimuli. Together, these findings demonstrate that the plant osmo-sensory components necessary to generate rapid osmotic-induced Ca(2+) responses remain responsive under varying osmolarities, endowing plants with the ability to perceive the dynamic intensities of water limitation imposed by osmotic stress.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, Food and Fuel for the 21st Century Center, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Stephan
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, Food and Fuel for the 21st Century Center, University of California, San Diego, La Jolla, CA 92093; School of Biological Sciences, Washington State University, Pullman, WA 99164.
authors.forename: Hans-Henning
authors.initials: HH
authors.lastname: Kunz
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, Food and Fuel for the 21st Century Center, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Eric
authors.initials: E
authors.lastname: Yang
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, Food and Fuel for the 21st Century Center, University of California, San Diego, La Jolla, CA 92093; jischroeder@ucsd.edu.
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D009154:Mutation; D064587:Osmoregulation / Q000187:drug effects; D009997:Osmotic Pressure; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D018087:Plastids / Q000378:metabolism; D027961:Potassium-Hydrogen Antiporters / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002121:Calcium Channel Blockers; D015220:Calcium Channels; C000589493:KEA1 protein, Arabidopsis; C000589494:KEA3 protein, Arabidopsis; D027961:Potassium-Hydrogen Antiporters; C501258:potassium transporter, Arabidopsis; D002118:Calcium
keywords: abscisic acid; calcium; osmotic sensing; plastid; salt stress