Title: Coexpressed subunits of dual genetic origin define a conserved supercomplex mediating essential protein import into chloroplasts

Abstract

In photosynthetic eukaryotes, thousands of proteins are translated in the cytosol and imported into the chloroplast through the concerted action of two translocons—termed TOC and TIC—located in the outer and inner membranes of the chloroplast envelope, respectively. The degree to which the molecular composition of the TOC and TIC complexes is conserved over phylogenetic distances has remained controversial. Here, we combine transcriptomic, biochemical, and genetic tools in the green alga Chlamydomonas (Chlamydomonas reinhardtii) to demonstrate that, despite a lack of evident sequence conservation for some of its components, the algal TIC complex mirrors the molecular composition of a TIC complex from Arabidopsis thaliana. The Chlamydomonas TIC complex contains three nuclear-encoded subunits, Tic20, Tic56, and Tic100, and one chloroplast-encoded subunit, Tic214, and interacts with the TOC complex, as well as with several uncharacterized proteins to form a stable supercomplex (TIC-TOC), indicating that protein import across both envelope membranes is mechanistically coupled. Expression of the nuclear and chloroplast genes encoding both known and uncharacterized TIC-TOC components is highly coordinated, suggesting that a mechanism for regulating its biogenesis across compartmental boundaries must exist. Conditional repression of Tic214, the only chloroplast-encoded subunit in the TIC-TOC complex, impairs the import of chloroplast proteins with essentialmore » roles in chloroplast ribosome biogenesis and protein folding and induces a pleiotropic stress response, including several proteins involved in the chloroplast unfolded protein response. These findings underscore the functional importance of the TIC-TOC supercomplex in maintaining chloroplast proteostasis.« less

Authors:

Ramundo, Silvia  ^[1];

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Asakura, Yukari ^[2]; Salomé, Patrice A.  ^[3];

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• Search DOE PAGES for ORCID "0000-0003-4452-9064"
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Strenkert, Daniela ^[3]; Boone, Morgane  ^[1];

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Mackinder, Luke C. M. ^[4]; Takafuji, Kazuaki ^[5]; Dinc, Emine ^[6]; Rahire, Michèle ^[6]; Crèvecoeur, Michèle ^[6]; Magneschi, Leonardo ^[7]; Schaad, Olivier  ^[8];

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Hippler, Michael  ^[9];

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Jonikas, Martin C.  ^[10];

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Merchant, Sabeeha ^[3]; Nakai, Masato  ^[2];

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Rochaix, Jean-David  ^[6];

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Walter, Peter  ^[1]

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+ Show Author Affiliations

1. Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143,, Howard Hughes Medical Institute, Chevy Chase, MD 20815,
2. Laboratory of Organelle Biology, Institute for Protein Research, Osaka University, Osaka 565-0871, Japan,
3. Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095,
4. Department of Biology, University of York, York YO10 5DD, United Kingdom,
5. Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan,
6. Department of Molecular Biology, University of Geneva, Geneva CH-1211, Switzerland,, Department of Plant Biology, University of Geneva, Geneva CH-1211, Switzerland,
7. Institute of Plant Biology and Biotechnology, University of Münster, Münster 48143, Germany,
8. Department of Biochemistry, University of Geneva, Geneva CH-1211, Switzerland,
9. Institute of Plant Biology and Biotechnology, University of Münster, Münster 48143, Germany,, Institute of Plant Science and Resources, Okayama University, Kurashiki 710-0046, Japan,
10. Howard Hughes Medical Institute, Chevy Chase, MD 20815,, Department of Molecular Biology, Princeton University, Princeton, NJ 08540

Publication Date:

2020-12-03

Research Org.:

Univ. of California, Los Angeles, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); European Molecular Biology Organization; Swiss National Science Foundation (SNSF); Belgian-American Educational Foundation; Humboldt Research Fellowship; German Research Foundation (DFG); Ministry of Science and Technology; National Institutes of Health (NIH)

OSTI Identifier:

1730999

Alternate Identifier(s):

OSTI ID: 1816800

Grant/Contract Number:  

FC02-02ER63421; LTF 563-2013; P2GEP3_148531; HI 739/9.1-739/9.2; 17H05668; 17H05725; 19H03183; 31003A_133089/1; HHMI826735-0012; R01GM032384

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 117 Journal Issue: 51; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; 54 ENVIRONMENTAL SCIENCES; chloroplast protein import; gene coexpression; chloroplast gene targeting; Chlamydomonas reinhardtii