Acclimation to Very Low CO₂: Contribution of Limiting CO₂ Inducible Proteins, LCIB and LCIA, to Inorganic Carbon Uptake in Chlamydomonas reinhardtii

• Published in: Plant physiology (Bethesda) Vol. 166; no. 4; pp. 2040 - 2050
• Main Authors: Wang, Yingjun, Spalding, Martin H.
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01.12.2014
• Subjects: Acclimatization; Biological Transport; Carbon - metabolism; Carbon Dioxide - metabolism; Chlamydomonas reinhardtii - genetics; Chlamydomonas reinhardtii - physiology; Chloroplasts; Evolution; Gene expression regulation; Genetic mutation; MEMBRANES, TRANSPORT, AND BIOENERGETICS; Mutation; Phenotypes; Photosynthesis; Plant cells; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Polymerase chain reaction
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.114.248294

The limiting-CO₂ inducible CO₂-concentrating mechanism (CCM) of microalgae represents an effective strategy to capture CO₂ when its availability is limited. At least two limiting-CO₂ acclimation states, termed low CO₂ and very low CO₂, have been demonstrated in the model microalga Chlamydomonas reinhardtii, and many questions still remain unanswered regarding both the regulation of these acclimation states and the molecular mechanism underlying operation of the CCM in these two states. This study examines the role of two proteins, Limiting CO₂ Inducible A (LCIA; also named NAR1.2) and LCIB, in the CCM of C. reinhardtii. The identification of an LCIA-LCIB double mutant based on its inability to survive in very low CO₂ suggests that both LCIA and LCIB are critical for survival in very low CO₂. The contrasting effects of individual mutations in LCIB and LCIA compared with the effects of LCIB-LCIA double mutations on growth and inorganic carbon-dependent photosynthetic O₂ evolution reveal distinct roles of LCIA and LCIB in the CCM. Although both LCIA and LCIB are essential for very low CO₂ acclimation, LCIB appears to function in a CO₂ uptake system, whereas LCIA appears to be associated with a HCO₃⁻ transport system. The contrasting and complementary roles of LCIA and LCIB in acclimation to low CO₂ and very low CO₂ suggest a possible mechanism of differential regulation of the CCM based on the inhibition of HCO₃⁻ transporters by moderate to high levels of CO₂.