GreenCut protein CPLD49 of Chlamydomonas reinhardtii associates with thylakoid membranes and is required for cytochrome b6f complex accumulation

• Published in: The Plant journal : for cell and molecular biology 2018-06, Vol.94 (6), p.1023-1037
• Main Authors: Wittkopp, Tyler M., Saroussi, Shai, Yang, Wenqiang, Johnson, Xenie, Kim, Rick G., Heinnickel, Mark L., Russell, James J., Phuthong, Witchukorn, Dent, Rachel M., Broeckling, Corey D., Peers, Graham, Lohr, Martin, Wollman, Francis‐André, Niyogi, Krishna K., Grossman, Arthur R.
• Format: Article
• Language: English
• Subjects: Accumulation; Algae; Chemical synthesis; Chlamydomonas reinhardtii; chloroplast; Coding; CPLD38; Cytochrome; cytochrome b6f; dehydrogenase; Electron transport; GreenCut; Heterotrophic organisms; Homology; Lipophilic; Membrane proteins; Membranes; Molecular chains; Nuclei; Photosynthesis; Proteins; Thylakoid membranes
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.13915

Summary The GreenCut encompasses a suite of nucleus‐encoded proteins with orthologs among green lineage organisms (plants, green algae), but that are absent or poorly conserved in non‐photosynthetic/heterotrophic organisms. In Chlamydomonas reinhardtii, CPLD49 (Conserved in Plant Lineage and Diatoms49) is an uncharacterized GreenCut protein that is critical for maintaining normal photosynthetic function. We demonstrate that a cpld49 mutant has impaired photoautotrophic growth under high‐light conditions. The mutant exhibits a nearly 90% reduction in the level of the cytochrome b6f complex (Cytb6f), which impacts linear and cyclic electron transport, but does not compromise the ability of the strain to perform state transitions. Furthermore, CPLD49 strongly associates with thylakoid membranes where it may be part of a membrane protein complex with another GreenCut protein, CPLD38; a mutant null for CPLD38 also impacts Cytb6f complex accumulation. We investigated several potential functions of CPLD49, with some suggested by protein homology. Our findings are congruent with the hypothesis that CPLD38 and CPLD49 are part of a novel thylakoid membrane complex that primarily modulates accumulation, but also impacts the activity of the Cytb6f complex. Based on motifs of CPLD49 and the activities of other CPLD49‐like proteins, we suggest a role for this putative dehydrogenase in the synthesis of a lipophilic thylakoid membrane molecule or cofactor that influences the assembly and activity of Cytb6f. Significance Statement Chlamydomonas GreenCut protein CPLD49 associates with thylakoid membranes, is required for normal photosynthetic activity and accumulation of the cytochrome b6f complex, and may interact with CPLD38, a green lineage‐conserved protein that is also required for normal cytochrome b6f complex accumulation.