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Plant Cell. 2015 Nov;27(11):3190-212. doi: 10.1105/tpc.15.00509. Epub 2015 Nov 3.

The EF-Hand Ca2+ Binding Protein MICU Choreographs Mitochondrial Ca2+ Dynamics in Arabidopsis.

Author information

1
Plant Energy Biology Lab, Institute of Crop Science and Resource Conservation, University of Bonn, 53113 Bonn, Germany.
2
Department of Biosciences, University of Milan, 20133 Milan, Italy.
3
Department of Biology, University of Padova, 35121 Padova, Italy.
4
Université d'Angers, INRA, Agrocampus Ouest, UMR 1345 Institut de Recherche en Horticulture et Semences, F-49045 Angers, France.
5
Plant Proteomics Group, Max-Planck-Institute for Plant Breeding Research, 50829 Cologne, Germany.
6
Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom.
7
ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, WA 6009, Australia.
8
Plant Proteomics Group, Max-Planck-Institute for Plant Breeding Research, 50829 Cologne, Germany Institute for Plant Biology and Biotechnology, University of Münster, 48149 Münster, Germany.
9
Department Chemical Signalling, Institute of Crop Science and Resource Conservation, University of Bonn, 53113 Bonn, Germany.
10
Department of Biosciences, University of Milan, 20133 Milan, Italy Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy.
11
Plant Energy Biology Lab, Institute of Crop Science and Resource Conservation, University of Bonn, 53113 Bonn, Germany markus.schwarzlander@uni-bonn.de.

Abstract

Plant organelle function must constantly adjust to environmental conditions, which requires dynamic coordination. Ca(2+) signaling may play a central role in this process. Free Ca(2+) dynamics are tightly regulated and differ markedly between the cytosol, plastid stroma, and mitochondrial matrix. The mechanistic basis of compartment-specific Ca(2+) dynamics is poorly understood. Here, we studied the function of At-MICU, an EF-hand protein of Arabidopsis thaliana with homology to constituents of the mitochondrial Ca(2+) uniporter machinery in mammals. MICU binds Ca(2+) and localizes to the mitochondria in Arabidopsis. In vivo imaging of roots expressing a genetically encoded Ca(2+) sensor in the mitochondrial matrix revealed that lack of MICU increased resting concentrations of free Ca(2+) in the matrix. Furthermore, Ca(2+) elevations triggered by auxin and extracellular ATP occurred more rapidly and reached higher maximal concentrations in the mitochondria of micu mutants, whereas cytosolic Ca(2+) signatures remained unchanged. These findings support the idea that a conserved uniporter system, with composition and regulation distinct from the mammalian machinery, mediates mitochondrial Ca(2+) uptake in plants under in vivo conditions. They further suggest that MICU acts as a throttle that controls Ca(2+) uptake by moderating influx, thereby shaping Ca(2+) signatures in the matrix and preserving mitochondrial homeostasis. Our results open the door to genetic dissection of mitochondrial Ca(2+) signaling in plants.

PMID:
26530087
PMCID:
PMC4682298
DOI:
10.1105/tpc.15.00509
[Indexed for MEDLINE]
Free PMC Article

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