Plant and Cell Physiology Advance Access published online on January 3, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcl066
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Induction of a high-CO2 inducible, periplasmic protein, H43, and its application as a high-CO2 responsive marker for study on high-CO2 sensing mechanism in Chlamydomonas reinhardtii
1Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8572 Japan
2Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502 Japan
Corresponding author; Yoshihiro Shiraiwa; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan; Tel: +81-29-853-4668; Fax: +81-29-853-6614; E-mail: emilhux{at}biol.tsukuba.ac.jp
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Abstract |
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The unicellular green alga Chlamydomonas reinhardtii can acclimate to a broad range of environmental CO2 concentrations. We observed that the cells synthesized a specific 43-kD protein, H43, in the periplasmic space under photoautotrophic high-CO2 conditions. Under low-CO2 conditions, H43 disappeared. However, H43 mRNA expression was observed even under heterotrophic low-CO2 conditions when the cells were grown with 17.4 mM acetate in darkness. When the cells were treated with 4,4'-dithiocyanatostilbene-2,2'-disulfonate (DIDS) and mersalyl to modify cell surface proteins, H43 mRNA expression was strongly affected under both heterotrophic and photoautotrophic conditions. H43 induction pattern in a mitochondrial respiration-deficient mutant dum-1 that lacks cytochrome c oxidase was the same, but the level was much lower than that in the wild type. Even under illumination, dissolved CO2 concentration in the culture rapidly increased slightly following the addition of acetate and dramatically increased even further by the inhibition of photosynthesis with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Radiotracer experiments with [U-14C] acetate revealed that 14CO2 release from cells was larger in darkness than in the light due to the great stimulation of internal CO2 evolution, resulting in an increase in external CO2 concentration. Strong light inhibited H43 induction and DCMU promoted the induction under heterotrophic low-CO2 conditions. The results demonstrate that H43 is strictly regulated by a concentration of CO2 resulted from respiration and photosynthesis. Our results suggest that Chlamydomonas induces high-CO2 responsive protein H43 by sensing the concentration of ambient CO2 with the contribution of cell surface protein.
Keywords: Chlamydomonas - CO2-responsive protein - High-CO2 acclimation - High-CO2 sensing - H43 - Periplasmic protein
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