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Plant Cell. 2019 Mar 12. pii: tpc.00936.2018. doi: 10.1105/tpc.18.00936. [Epub ahead of print]

Channelrhodopsin-1 phosphorylation changes with the phototactic behavior and responds to physiological stimuli in Chlamydomonas.

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Friedrich-Alexander University Erlangen CITY: Erlangen Germany [DE].
Jawaharlal Nehru University CITY: New Delhi India [IN].
Humboldt University CITY: Berlin Germany [DE].
Friedrich-Alexander University Erlangen CITY: Erlangen POSTAL_CODE: 91058 Germany [DE]


The unicellular alga Chlamydomonas reinhardtii exhibits oriented movement responses (phototaxis) to light over more than three log units of intensity. Phototaxis thus depends on the cell's ability to adjust the sensitivity of the involved photoreceptors to the ambient light conditions. In C. reinhardtii these are the channelrhodopsins ChR1 and ChR2, which are plasma membrane located light-gated cation channels. Although ChRs are widely used in optogenetic studies, knowledge about ChR signaling in alga is still limited. We characterized the in vivo phosphorylation of ChR1. Its reversible phosphorylation occurred within seconds as a graded response to changes in the light intensity and ionic composition of the medium and depended on an elevated cytosolic Ca2+ concentration. Changes in the phototactic sign were accompanied by alterations in the ChR1 phosphorylation status. Furthermore, compared with the wild-type, a permanently negative phototactic mutant required higher light intensities to evoke ChR1 phosphorylation. C-terminal ChR1 truncation disturbed the reversible phosphorylation, whereas it was normal in ChR2-knockout and eyespot-assembly mutants. Newly identified phosphosites in regions important for ChR1 function point to their potential regulatory role(s). We propose that multiple ChR1 phosphorylation, regulated via a Ca2+-based feedback loop, is one important component in the adaptation of phototactic sensitivity in Chlamydomonas.


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