title: Chloroplast-mediated regulation of CO2-concentrating mechanism by Ca2+-binding protein CAS in the green alga Chlamydomonas reinhardtii.
abstract: Aquatic photosynthetic organisms, including the green alga Chlamydomonas reinhardtii, induce a CO2-concentrating mechanism (CCM) to maintain photosynthetic activity in CO2-limiting conditions by sensing environmental CO2and light availability. Previously, a novel high-CO2-requiring mutant, H82, defective in the induction of the CCM, was isolated. A homolog of calcium (Ca2+)-binding protein CAS, originally found in Arabidopsis thaliana, was disrupted in H82 cells. Although Arabidopsis CAS is reported to be associated with stomatal closure or immune responses via a chloroplast-mediated retrograde signal, the relationship between a Ca2+signal and the CCM associated with the function of CAS in an aquatic environment is still unclear. In this study, the introduction of an intact CAS gene into H82 cells restored photosynthetic affinity for inorganic carbon, and RNA-seq analyses revealed that CAS could function in maintaining the expression levels of nuclear-encoded CO2-limiting-inducible genes, including the HCO3-transporters high-light activated 3 (HLA3) and low-CO2-inducible gene A (LCIA). CAS changed its localization from dispersed across the thylakoid membrane in high-CO2conditions or in the dark to being associated with tubule-like structures in the pyrenoid in CO2-limiting conditions, along with a significant increase of the fluorescent signals of the Ca2+indicator in the pyrenoid. Chlamydomonas CAS had Ca2+-binding activity, and the perturbation of intracellular Ca2+homeostasis by a Ca2+-chelator or calmodulin antagonist impaired the accumulation of HLA3 and LCIA. These results suggest that Chlamydomonas CAS is a Ca2+-mediated regulator of CCM-related genes via a retrograde signal from the pyrenoid in the chloroplast to the nucleus.
authors: Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors: Lianyong
authors: L
authors: Wang
authors: Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors: Takashi
authors: T
authors: Yamano
authors: Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors: Shunsuke
authors: S
authors: Takane
authors: Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors: Yuki
authors: Y
authors: Niikawa
authors: Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors: Chihana
authors: C
authors: Toyokawa
authors: Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan.
authors: Shin-Ichiro
authors: SI
authors: Ozawa
authors: Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki 444-8585, Japan.
authors: Ryutaro
authors: R
authors: Tokutsu
authors: Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan.
authors: Yuichiro
authors: Y
authors: Takahashi
authors: Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki 444-8585, Japan.
authors: Jun
authors: J
authors: Minagawa
authors: NODAI Genome Research Center, Tokyo University of Agriculture, Tokyo 156-8502, Japan.
authors: Yu
authors: Y
authors: Kanesaki
authors: Department of Bioscience, Tokyo University of Agriculture, Tokyo 156-8502, Japan.
authors: Hirofumi
authors: H
authors: Yoshikawa
authors: Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan; fukuzawa@lif.kyoto-u.ac.jp.
authors: Hideya
authors: H
authors: Fukuzawa
mesh_terms: D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D020524:Thylakoids / Q000235:genetics / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D010940:Plant Proteins; D002245:Carbon Dioxide; D002118:Calcium
keywords: acclimation; bicarbonate transporter; calcium signaling; photosynthesis; pyrenoid