The calcium sensing receptor (CAS) and calcium are involved in the high-light response of Chlamydomonas reinhardtii
Andreas Busch, Dimitris Petroutsos, Ingrid Hirschmann, Susan Hawat, and Michael Hippler
Institute of Plant Biochemistry and Biotechnology, University of Muenster, Hindenburgplatz 55, 48143 Muenster, Germany
CAS is a plant specific putative calcium binding protein localized in the thylakoid membrane of the chloroplasts. Arabidopsis CAS knock-out mutants show impaired stomatal closure upon ap-plication of exogenous Ca2+ and lack of cytosolic calcium transients induced by extracellular calcium (Nomura et al, 2008, Weinl et al, 2008). In Chlamydomonas CAS is induced about four times under iron deficiency (Naumann et al. 2007) and two times under high light (HL). To elucidate the role of CAS in Chlamydomonas we generated four independent CAS knock-down Chlamydomonas lines (cas-kd). Upon shift to HL conditions, cas-kd lines are unable to fully induce LhcSR3, a protein crucial for non-photochemical quenching (Peers et al., 2009). Prolonged exposure of cas-kd lines to HL leads to their death. Interestingly, the addition of exogenous Ca2+ rescues both the induction of LhcSR3 and the growth of cas-kd lines under HL. To further elucidate the role of Ca2+ as signaling molecule in the HL adaptation, inhibitor studies were performed. Under HL conditions, LhcSR3 expression in wild type cells was inhibited by the calmodulin antagonist W7, whereas cells treated with W5 normally induced LhcsSR3. In summary we propose that CAS and calcium are involved in the high-light response of Chlamydomonas reinhardtii.

(1) Nomura et al 2008 Plant J, 53: 988-98 (2) Weinl et al 2008 New Phytol 179: 675-86 (3) Naumann et al 2007 Proteomics 7: 3964-79 (4) Peers et al 2009 Nature 426: 518-21
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