A chloroplast-localized mitochondrial calcium uniporter transduces osmotic stress in Arabidopsis

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Abstract

Chloroplasts are integral to sensing biotic and abiotic stress in plants, but their role in transducing Ca2+-mediated stress signals remains poorly understood1,2. Here we identify cMCU, a member of the mitochondrial calcium uniporter (MCU) family, as an ion channel mediating Ca2+ flux into chloroplasts in vivo. Using a toolkit of aequorin reporters targeted to chloroplast stroma and the cytosol in cMCU wild-type and knockout lines, we provide evidence that stress-stimulus-specific Ca2+ dynamics in the chloroplast stroma correlate with expression of the channel. Fast downstream signalling events triggered by osmotic stress, involving activation of the mitogen-activated protein kinases (MAPK) MAPK3 and MAPK6, and the transcription factors MYB60 and ethylene-response factor 6 (ERF6), are influenced by cMCU activity. Relative to wild-type plants, cMCU knockouts display increased resistance to long-term water deficit and improved recovery on rewatering. Modulation of stromal Ca2+ in specific processing of stress signals identifies cMCU as a component of plant environmental sensing.

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Fig. 1: cMCU localizes to chloroplasts in Arabidopsis mesophyll cells.
Fig. 2: Recombinant cMCU mediates Ca2+ fluxes in electrophysiological experiments and in a heterologous expression system.
Fig. 3: Monitoring of stromal Ca2+ concentration reveals differential calcium dynamics and signalling in wild-type versus cMCU knockout plants.
Fig. 4: Plants lacking cMCU are drought resistant and recover quickly following rewatering.

Data availability

The data that support the findings of this study are available from the corresponding authors upon request.

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Acknowledgements

The authors thank A. Weber, D. Leister, A. Costa, G. Finazzi, W. Martin and F. Lo Schiavo for useful discussions. We thank Human Frontiers Science Program (HFSP RG0052 to I.S.), the University of Padova (PRID 2018 prot. BIRD180317 to L.N. and STARS (Supporting Talents in Research project) to L.Carraretto), the MIUR (FFABR 2017 to E.F.), the EU within the Marie-Curie ITN CALIPSO (FP7, Project no. 607607 to U.C.V.) for financial support.

Author information

I.S., L.N., L.Cendron, E.F. and E.T. designed experiments; E.T., L.Carraretto, R.M., E.C., M.V., M.F., L.M. and S.D.B. performed experiments; I.S., L.N., L.Cendron, L.Carraretto, E.F., E.T., T.C. and U.C.V. analysed data; I.S., L.N., L.Cendron, E.F. and E.T. wrote the manuscript. I.S., L.N., E.F., U.C.V. and L.Carraretto acquired funding.

Correspondence to Elide Formentin or Lorella Navazio or Ildiko Szabo.

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The authors declare no competing interests.

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Journal peer review information: Nature Plants thanks Jose Feijo, Simon Stael and Tou Cheu Xiong for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figures 1–17, Supplementary Video legends, Supplementary Table 1, Supplementary Materials and Methods, and Supplementary References.

Reporting Summary

Supplementary Video 1

Plants stably expressing mitochondrial β-F1-ATPase-EGFP (green) that have been transformed with cMCU::tdTomato (red).

Supplementary Video 2

cMCU::EGFP in epidermal cells stained with TMRM, a dye that accumulates in the mitochondria in a membrane potential-dependent manner

Supplementary Video 3

cMCU::EGFP in epidermal cells.

Supplementary Video 4

cMCU::EGFP in guard cells stained with TMRM (accumulates in mitochondria).

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Teardo, E., Carraretto, L., Moscatiello, R. et al. A chloroplast-localized mitochondrial calcium uniporter transduces osmotic stress in Arabidopsis. Nat. Plants 5, 581–588 (2019) doi:10.1038/s41477-019-0434-8

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