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Nat Commun. 2019 Aug 16;10(1):3703. doi: 10.1038/s41467-019-11698-5.

Ca2+-regulated Ca2+ channels with an RCK gating ring control plant symbiotic associations.

Author information

1
Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
2
Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
3
Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA.
4
School of Life Science and Technology, ShanghaiTech University, 201210, Shanghai, China.
5
School of Agriculture, University of Wisconsin-Platteville, Platteville, WI, USA.
6
Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA. youxing.jiang@utsouthwestern.edu.
7
Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA. youxing.jiang@utsouthwestern.edu.

Abstract

A family of plant nuclear ion channels, including DMI1 (Does not Make Infections 1) and its homologs CASTOR and POLLUX, are required for the establishment of legume-microbe symbioses by generating nuclear and perinuclear Ca2+ spiking. Here we show that CASTOR from Lotus japonicus is a highly selective Ca2+ channel whose activation requires cytosolic/nucleosolic Ca2+, contrary to the previous suggestion of it being a K+ channel. Structurally, the cytosolic/nucleosolic ligand-binding soluble region of CASTOR contains two tandem RCK (Regulator of Conductance for K+) domains, and four subunits assemble into the gating ring architecture, similar to that of large conductance, Ca2+-gated K+ (BK) channels despite the lack of sequence similarity. Multiple ion binding sites are clustered at two locations within each subunit, and three of them are identified to be Ca2+ sites. Our in vitro and in vivo assays also demonstrate the importance of these gating-ring Ca2+ binding sites to the physiological function of CASTOR as well as DMI1.

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