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Insights into degradation and targeting of the photoreceptor channelrhodopsin-1
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  • Michaela Wolfram,
  • Arne Greif,
  • Olga Baidukova,
  • Hildegard Voll,
  • Sandra Tauber,
  • Jana Lindacher,
  • Peter Hegemann,
  • Georg Kreimer
Michaela Wolfram
Friedrich-Alexander-Universitat Erlangen-Nurnberg Institut fur Biologie
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Arne Greif
Friedrich-Alexander-Universitat Erlangen-Nurnberg Institut fur Biologie
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Olga Baidukova
Humboldt-Universitat zu Berlin Institut fur Biologie
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Hildegard Voll
Friedrich-Alexander-Universitat Erlangen-Nurnberg Institut fur Biologie
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Sandra Tauber
Friedrich-Alexander-Universitat Erlangen-Nurnberg Institut fur Biologie
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Jana Lindacher
Friedrich-Alexander-Universitat Erlangen-Nurnberg Institut fur Biologie
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Peter Hegemann
Humboldt-Universitat zu Berlin Institut fur Biologie
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Georg Kreimer
Friedrich-Alexander-Universitat Erlangen-Nurnberg Institut fur Biologie

Corresponding Author:[email protected]

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Abstract

In Chlamydomonas, the directly light-gated, plasma membrane-localized (PM) cation channels channelrhodopsins ChR1 and ChR2 are the primary photoreceptors for phototaxis. Their targeting and abundance is essential for optimal movement responses. However, our knowledge how Chlamydomonas achieves this is still at its infancy. Here we show that ChR1 internalization occurs via light-stimulated endocytosis. Prior or during endocytosis ChR1 is modified and forms high molecular mass complexes. These are the solely detectable ChR1 forms in extracellular vesicles (EVs) and their abundance therein dynamically changes upon illumination. The ChR1-containing EVs are secreted via the PM and/or the ciliary base. In line with this, ciliogenesis mutants exhibit increased ChR1 degradation rates. Further, we establish involvement of two cysteine proteases in its turnover: CEP1, a papain-type C1A member, and a calpain. ΔCEP1 knock-out strains lack light-induced ChR1 degradation, whereas ChR2 degradation was unaffected. Low light stimulates CEP1 expression, which is regulated via phototropin, a SPA1 E3 ubiquitin ligase and cAMP. Further, mutant and inhibitor analyses revealed involvement of the small GTPase ARL11 and SUMOylation in ChR1 targeting to the eyespot and cilia. Our study thus defines the degradation pathway of this central photoreceptor of Chlamydomonas and identifies novel elements involved in its homeostasis and targeting.
21 Mar 2024Submitted to Plant, Cell & Environment
21 Mar 2024Submission Checks Completed
21 Mar 2024Assigned to Editor
21 Mar 2024Review(s) Completed, Editorial Evaluation Pending
15 May 2024Editorial Decision: Revise Minor
07 Jun 2024Review(s) Completed, Editorial Evaluation Pending
08 Jun 2024Reviewer(s) Assigned
11 Jun 2024Editorial Decision: Accept