CAS Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, No.7 Nanhai Road, Qingdao, 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, No.1 Wenhai Road, Jimo, Qingdao, 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, No.7 Nanhai Road, Qingdao, 266071, China; State Key Laboratory of Bioactive Seaweed Substances, Qingdao Brightmoon Seaweed Group Co Ltd, No.777 Mingyue Road, Qingdao, 266400, China. Electronic address: [Email]
Brown algae play a dominant role in the primary productivity of coastal ecosystems and may have an efficient carbon fixation. In this work, 56 genes involved in inorganic carbon fixation were identified from the Saccharina japonica genome. Sequence structure analysis of these genes showed the existence of corresponding function domains and active amino acid sites highly conserved with other stramenopile species. The predicted subcellular localizations showed that Calvin cycle-related enzymes predominantly reside in the plastid and that putative C4-related enzymes are mainly distributed in the mitochondrion. We determined the transcriptional profiles and enzymatic activities of these C4-related enzymes in response to the KHCO3 concentrations and light intensities. Pyruvate orthophosphate dikinase (PPDK) presented the greatest response to low HCO3- concentrations and high light intensity. Phosphoenolpyruvate carboxykinase (PEPCK) was up-regulated at low HCO3- concentrations to compensate for ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and might be the crucial decarboxylase in this kelp. We propose that S. japonica might possess a PPDK- and PEPCK-dependent C4-like pathway that enables its rapid growth in natural coastal environments.