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Transient cell-specific EXO70A1 activity in the CASP domain and Casparian strip localization

Nature Plants volume 3, Article number: 17058 (2017) Cite this article

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Abstract

In a striking case of evolutionary convergence, polarized cell layers with ring-like diffusion barriers have evolved in both plant and animal lineages independently. In plants, ring-like Casparian strips become localized by the CASPARIAN STRIP MEMBRANE DOMAIN PROTEINS (CASPs). The mechanism of this striking localization, however, has remained enigmatic. Here we present a genetic screen aimed at isolating determinants of CASP localization. One of the mutants, lord of the rings 2 (lotr2)/exo70a1, displays dramatic de-localization of CASPs into randomly localized microdomains. EXO70A1 is a subunit of the exocyst complex, a central component of secretion in eukaryotes. Irradiation of EXO70 subunit genes in plants has suggested specialization of this conserved complex. Intriguingly, lotr2/exo70a1 does neither affect secretion of the CASPs, nor that of other membrane proteins in the endodermis, thus separating exocyst activity in localization from a general defect in secretion. Our results establish EXO70A1 as a central player in Casparian strip formation, generating a transient positional information that will be translated into a precisely localized cell wall modification.

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Figure 1: EXO70A1 is necessary for CASP1 positioning and Casparian strip integrity.
Figure 2: EXO70A1 is required for the central CASP domain but not for lateral polarity.
Figure 3: Local EXO70A1 accumulation is necessary for CASP1 and exocyst positioning in the endodermis.
Figure 4: Endodermal PtdIns(4,5)P2 accumulation at the central domain requires EXO70A1.
Figure 5: Schematic model of exocyst-mediated localization of CASPs during endodermal differentiation.

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Acknowledgements

We thank the Central Imaging Facility (CIF) and the Genomic Technologies Facility (GTF) of the University of Lausanne for technical support. B.M. Humbel of the Electron Microscopy Facility (EMF) for expert technical assistance and input, V. Žárský and Y. Jaillais for sharing published material. T. Fitzpatrick of the University of Geneva for kindly providing green house facilities. The Nottingham Arabidopsis Stock Centre (NASC) is acknowledged for providing seeds. J.E.M. Vermeer, J. Alassimone, S. Ammar, C. Schwab, P. Marhavy, J. Weber, I. Acosta, M. Sankar and E. Schmid are thanked for technical expertise, assistance and helpful discussions. This work was funded by grants from the Swiss National Science Foundation (SNF) and the European Research Council (ERC) to N.G., by a short term fellowship of the Société Académique Vaudoise to L. K., by the AgreenSkills+ fellowship programme which has received funding from the EU's Seventh Framework Programme under grant agreement no. FP7-609398 and the LabEx Saclay Plant Sciences-SPS (ANR-10-LABX-0040-SPS) to K.H. (IJPB), by a Japanese Society for the Promotion of Science (JSPS) postdoctoral fellowship for research abroad to S.F., and by an EMBO long-term postdoctoral fellowship to M. B.

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  1. Lothar Kalmbach

    Present address: †Present address: Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge CB2 1LR, UK.,

Authors and Affiliations

  1. Department of Plant Molecular Biology, University of Lausanne, Biophore Building, UNIL-Sorge, 1015 Lausanne, Switzerland

    Lothar Kalmbach, Kian Hématy, Damien De Bellis, Marie Barberon, Satoshi Fujita, Robertas Ursache & Niko Geldner

  2. Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, 78000 Versailles, France

    Kian Hématy

  3. Electron Microscopy Facility, University of Lausanne, Biophore Building, UNIL-Sorge, 1015 Lausanne, Switzerland

    Damien De Bellis & Jean Daraspe

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Contributions

L.K., K.H. and N.G. designed experiments, L.K., K.H., D.D.B., M.B., S.F., J.D. performed experiments L.K., K.H., D.D.B., J.D. and N.G. interpreted the results. R.U. provided unpublished protocols. Manuscript written by L.K., K.H. and N.G. All authors edited and commented on the manuscript.

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Correspondence to Niko Geldner.

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Supplementary information

Supplementary Information

Supplementary Figures 1–8, legend for Supplementary Video 1, Supplementary Methods and Material, Supplementary Tables 1–3, Supplementary References. (PDF 10121 kb)

Supplementary Video 1

CASP1-GFP gradually accumulates at ectopic patches in exo70a1. (AVI 6142 kb)

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Kalmbach, L., Hématy, K., De Bellis, D. et al. Transient cell-specific EXO70A1 activity in the CASP domain and Casparian strip localization. Nature Plants 3, 17058 (2017). https://doi.org/10.1038/nplants.2017.58

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