The Ca(2+) Sensor SCaBP3/CBL7 Modulates Plasma Membrane H(+)-ATPase Activity and Promotes Alkali Tolerance in Arabidopsis.

1. Plant Cell. 2019 Jun;31(6):1367-1384. doi: 10.1105/tpc.18.00568. Epub 2019 Apr 8. The Ca(2+) Sensor SCaBP3/CBL7 Modulates Plasma Membrane H(+)-ATPase Activity and Promotes Alkali Tolerance in Arabidopsis. Yang Y(1), Wu Y(1), Ma L(1), Yang Z(1), Dong Q(2), Li Q(1), Ni X(1), Kudla J(2), Song C(3), Guo Y(4)(5). Author information: (1)State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China. (2)Institut für Biologie und Biotechnologie der Pflanzen, Universität Münster, 48149 Münster, Germany. (3)Collaborative Innovation Center of Crop Stress Biology, Henan Province, Institute of Plant Stress Biology, Henan University, Kaifeng 475001, China. (4)State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China guoyan@cau.edu.cn. (5)Joint Laboratory for International Cooperation in Crop Molecular Breeding, China Agricultural University, Beijing 100193, China. Saline-alkali soil is a major environmental constraint impairing plant growth and crop productivity. In this study, we identified a Ca2+ sensor/kinase/plasma membrane (PM) H+-ATPase module as a central component conferring alkali tolerance in Arabidopsis (Arabidopsis thaliana). We report that the SCaBP3 (SOS3-LIKE CALCIUM BINDING PROTEIN3)/CBL7 (CALCINEURIN B-LIKE7) loss-of-function plants exhibit enhanced stress tolerance associated with increased PM H+-ATPase activity and provide fundamental mechanistic insights into the regulation of PM H+-ATPase activity. Consistent with the genetic evidence, interaction analyses, in vivo reconstitution experiments, and determination of H+-ATPase activity indicate that interaction of the Ca2+ sensor SCaBP3 with the C-terminal Region I domain of the PM H+-ATPase AHA2 (Arabidopsis thaliana PLASMA MEMBRANE PROTON ATPASE2) facilitates the intramolecular interaction of the AHA2 C terminus with the Central loop region of the PM H+-ATPase to promote autoinhibition of H+-ATPase activity. Concurrently, direct interaction of SCaPB3 with the kinase PKS5 (PROTEIN KINASE SOS2-LIKE5) stabilizes the kinase-ATPase interaction and thereby fosters the inhibitory phosphorylation of AHA2 by PKS5. Consistently, yeast reconstitution experiments and genetic analysis indicate that SCaBP3 provides a bifurcated pathway for coordinating intramolecular and intermolecular inhibition of PM H+-ATPase. We propose that alkaline stress-triggered Ca2+ signals induce SCaBP3 dissociation from AHA2 to enhance PM H+-ATPase activity. This work illustrates a versatile signaling module that enables the stress-responsive adjustment of plasma membrane proton fluxes. © 2019 American Society of Plant Biologists. All rights reserved. DOI: 10.1105/tpc.18.00568 PMCID: PMC6588306 PMID: 30962395 [Indexed for MEDLINE]