One of the critical parts of the CO(2) perception mechanisms in algae has now been identified in a marine diatom, an important finding since diatoms are the major primary producer in the ocean. Increasing CO(2) might probably be sensed directly by the cAMP forming enzyme, adenylyl cyclase, and cytosolic cAMP represses expression of CCM components in marine diatoms. Upstream sequences of CO(2)-responsive genes, ptca1 and 2, for carbonic anhydrases (CA) in the marine diatom Phaeodactylum tricornutum, were recently isolated and characterized. Promoters for both ptca1 and 2 possess at least 5 CREs respectively at -10 to -330 and at -330 to -630 relative to each transcription-start site. Our recent experiments clearly showed that one of CREs, located at -70 to -63 of the ptca1 promoter, exhibited a primary role in repressing the ptca1 promoter under high CO(2) or in the dark. Truncations of CREs in the ptca2 promoter also resulted in derepressions of the ptca2 gene in high CO(2). This addendum will discuss the implication of acquiring repression systems for the CCM and the possible impact of the repression of the CCM following a direct perception of elevated [CO(2)] in the marine environment.
Keywords: cAMP; cAMP-response element; carbon dioxide; carbonic anhydrase; marine diatom; promoter.