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Article

Mg2+ is a Missing Link in Plant Cell Ca2+ Signalling and Homeostasis—A Study on Vicia faba Guard Cells

1
King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering (BESE), Thuwal 23955-6900, Saudi Arabia
2
Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT 06030, USA
3
King Abdullah University of Science and Technology (KAUST), Computational Bioscience Research Center (CBRC), Thuwal 23955-6900, Saudi Arabia
4
Centre de Biochimie Structurale, CNRS, INSERM, Université de Montpellier, 34090 Montpellier, France
5
Department of Chemistry, Biology & Biotechnology, University of Perugia, 06121 Perugia, Italy
*
Authors to whom correspondence should be addressed.
Int. J. Mol. Sci. 2020, 21(11), 3771; https://doi.org/10.3390/ijms21113771
Received: 28 March 2020 / Revised: 13 May 2020 / Accepted: 15 May 2020 / Published: 27 May 2020
(This article belongs to the Special Issue New Horizons in Plant Cell Signaling)
Hyperpolarization-activated calcium channels (HACCs) are found in the plasma membrane and tonoplast of many plant cell types, where they have an important role in Ca2+-dependent signalling. The unusual gating properties of HACCs in plants, i.e., activation by membrane hyperpolarization rather than depolarization, dictates that HACCs are normally open in the physiological hyperpolarized resting membrane potential state (the so-called pump or P-state); thus, if not regulated, they would continuously leak Ca2+ into cells. HACCs are permeable to Ca2+, Ba2+, and Mg2+; activated by H2O2 and the plant hormone abscisic acid (ABA); and their activity in guard cells is greatly reduced by increasing amounts of free cytosolic Ca2+ ([Ca2+]Cyt), and hence closes during [Ca2+]Cyt surges. Here, we demonstrate that the presence of the commonly used Mg-ATP inside the guard cell greatly reduces HACC activity, especially at voltages ≤ −200 mV, and that Mg2+ causes this block. Therefore, we firstly conclude that physiological cytosolic Mg2+ levels affect HACC gating and that channel opening requires either high negative voltages (≥−200 mV) or displacement of Mg2+ away from the immediate vicinity of the channel. Secondly, based on structural comparisons with a Mg2+-sensitive animal inward-rectifying K+ channel, we propose that the likely candidate HACCs described here are cyclic nucleotide gated channels (CNGCs), many of which also contain a conserved diacidic Mg2+ binding motif within their pores. This conclusion is consistent with the electrophysiological data. Finally, we propose that Mg2+, much like in animal cells, is an important component in Ca2+ signalling and homeostasis in plants. View Full-Text
Keywords: hyperpolarization-activated calcium channels; HACCs; cyclic nucleotides-activated channels; CNGCs; magnesium; calcium; guard cells; patch clamp; cellular homeostasis; structure modelling hyperpolarization-activated calcium channels; HACCs; cyclic nucleotides-activated channels; CNGCs; magnesium; calcium; guard cells; patch clamp; cellular homeostasis; structure modelling
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MDPI and ACS Style

Lemtiri-Chlieh, F.; Arold, S.T.; Gehring, C. Mg2+ is a Missing Link in Plant Cell Ca2+ Signalling and Homeostasis—A Study on Vicia faba Guard Cells. Int. J. Mol. Sci. 2020, 21, 3771. https://doi.org/10.3390/ijms21113771

AMA Style

Lemtiri-Chlieh F, Arold ST, Gehring C. Mg2+ is a Missing Link in Plant Cell Ca2+ Signalling and Homeostasis—A Study on Vicia faba Guard Cells. International Journal of Molecular Sciences. 2020; 21(11):3771. https://doi.org/10.3390/ijms21113771

Chicago/Turabian Style

Lemtiri-Chlieh, Fouad, Stefan T. Arold, and Chris Gehring. 2020. "Mg2+ is a Missing Link in Plant Cell Ca2+ Signalling and Homeostasis—A Study on Vicia faba Guard Cells" International Journal of Molecular Sciences 21, no. 11: 3771. https://doi.org/10.3390/ijms21113771

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