Abstract
Marine diatoms can concentrate inorganic carbon (Ci) under air level pCO2. Accumulated Ci is thought to be delivered to Rubisco efficiently catalysed by internal carbonic anhydrases (CAs). In the marine diatom Phaeodactylum tricornutum, two chloroplastic CAs, PtCA1 and 2, were so far identified and its localization in the pyrernoid is strongly suggested. Other 6 putative cas are found in P. tricornutum genome but their localization is unknown. It's also suggested C4 metabolism is a part of the diatom CCMs. If this is the case in P. tricornutum, PEPC, a HCO3- fixation enzyme, most probably locate in the cytosol and, PEPCK or ME, decarboxylation enzymes, need to locate in the chloroplast. In the present study, putative CAs and C4 genes were cloned from P. tricornutum cDNA library. Expressions of these genes were analyzed by RT-PCR. These 6 putative cas and C4 component genes were fused with egfp and induced into the cells of P. tricornutum. As a result, all 6 putative CAs were localized at the four-layered membrane systems surrounding the chloroplast. The mechanisms how diatom cells control the Ci flux inside the cytosol and the chloroplast will be discussed from these results.
