Journal
PLANT PHYSIOLOGY
Volume 182, Issue 4, Pages 1883-1893Publisher
AMER SOC PLANT BIOLOGISTS
DOI: 10.1104/pp.19.01587
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Funding
- Japan Society for the Promotion of Science (KAKENHI) [16H04805, 16K07399, 17J08280]
- Japan Science and Technology Agency, Advanced Low Carbon Technology Research and Development Program [JPMJAL1105]
- Council for Science, Technology, and Innovation, Cabinet Office, Government of Japan (ImPACT program)
- Kyoto University Research Development Program [ISHIZUE 2019]
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Mutants with abnormal LCIB localization reveal the importance of starch sheath formation for the CO2-concentrating mechanism in the green alga Chlamydomonas reinhardtii. Aquatic photosynthetic organisms induce a CO2-concentrating mechanism (CCM) to overcome the difficulty of acquiring inorganic carbon under CO2-limiting conditions. As part of the CCM, the CO2-fixing enzyme Rubisco is enriched in the pyrenoid located in the chloroplast, and, in many green algae, several thick starch plates surround the pyrenoid to form a starch sheath. In Chlamydomonas reinhardtii, low-CO2-inducible protein B (LCIB), which is an essential factor for the CCM, displays altered cellular localization in response to a decrease in environmental CO2 concentration, moving from dispersed throughout the chloroplast stroma to around the pyrenoid. However, the mechanism behind LCIB migration remains poorly understood. Here, we report the characteristics of an Isoamylase1-less mutant (4-D1), which shows aberrant LCIB localization and starch sheath formation. Under very-low-CO2 conditions, 4-D1 showed retarded growth, lower photosynthetic affinities against inorganic carbon, and a decreased accumulation level of the HCO3- transporter HLA3. The aberrant localization of LCIB was also observed in another starch-sheathless mutant sta11-1, but not in sta2-1, which possesses a thinned starch sheath. These results suggest that the starch sheath around the pyrenoid is required for the correct localization of LCIB and for the operation of CCM.
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