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Elife. 2019 Oct 15;8. pii: e49577. doi: 10.7554/eLife.49577.

The Mars1 kinase confers photoprotection through signaling in the chloroplast unfolded protein response.

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Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States.
Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States.
Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States.
Department of Molecular Biology, Princeton University, Princeton, United States.


In response to proteotoxic stress, chloroplasts communicate with the nuclear gene expression system through a chloroplast unfolded protein response (cpUPR). We isolated Chlamydomonas reinhardtii mutants that disrupt cpUPR signaling and identified a gene encoding a previously uncharacterized cytoplasmic protein kinase, termed Mars1-for mutant affected in chloroplast-to-nucleus retrograde signaling-as the first known component in cpUPR signal transmission. Lack of cpUPR induction in MARS1 mutant cells impaired their ability to cope with chloroplast stress, including exposure to excessive light. Conversely, transgenic activation of cpUPR signaling conferred an advantage to cells undergoing photooxidative stress. Our results indicate that the cpUPR mitigates chloroplast photodamage and that manipulation of this pathway is a potential avenue for engineering photosynthetic organisms with increased tolerance to chloroplast stress.


cell biology; chlamydomonas reinhardtii; chloroplast-to-nucleus signaling; genetics; genomics; organellar protein homeostasis; photoprotection

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