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      Tip-localized Ca2+ -permeable channels control pollen tube growth via kinase-dependent R- and S-type anion channel regulation.

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          Pollen tubes (PTs) are characterized by having tip-focused cytosolic calcium ion (Ca2+ ) concentration ([Ca2+ ]cyt ) gradients, which are believed to control PT growth. However, the mechanisms by which the apical [Ca2+ ]cyt orchestrates PT growth are not well understood. Here, we aimed to identify these mechanisms by combining reverse genetics, cell biology, electrophysiology, and live-cell Ca2+ and anion imaging. We triggered Ca2+ -channel activation by applying hyperpolarizing voltage pulses and observed that the evoked [Ca2+ ]cyt increases were paralleled by high anion channel activity and a decrease in the cytosolic anion concentration at the PT tip. We confirmed a functional correlation between these patterns by showing that inhibition of Ca2+ -permeable channels eliminated the [Ca2+ ]cyt increase, resulting in the abrogation of anion channel activity via Ca2+ -dependent protein kinases (CPKs). Functional characterization of CPK and anion-channel mutants revealed a CPK2/20/6-dependent activation of SLAH3 and ALMT12/13/14 anion channels. The impaired growth phenotypes of anion channel and CPK mutants support the physiological significance of a kinase- and Ca2+ -dependent pathway to control PT growth via anion channel activation. Other than unveiling this functional link, our membrane hyperpolarization method allows for unprecedented manipulation of the [Ca2+ ]cyt gradient or oscillations in the PT tips and opens an array of opportunities for channel screenings.

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          Author and article information

          New Phytol.
          The New phytologist
          May 2018
          : 218
          : 3
          [1 ] Department of Botany I, Julius-Von-Sachs Institute for Biosciences, University of Wuerzburg, 97082, Wuerzburg, Germany.
          [2 ] Plant Biochemistry, Dahlem Centre of Plant Sciences, FU Berlin, Königin-Luise-Straße 12/16, 14195, Berlin, Germany.
          [3 ] Organismal and Evolutionary Biology Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, 00014, Helsinki, Finland.
          [4 ] Institute of Technology, University of Tartu, Nooruse 1, 50411, Tartu, Estonia.
          [5 ] Department of Cell Biology & Molecular Genetics, University of Maryland, 2136 Bioscience Research Building, College Park, MD, 20742-5815, USA.


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