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Published on September 29, 2006; 10.1104/pp.106.086561

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Received July 11, 2006
Accepted September 21, 2006

CO2 Sensing at Ocean Surface Mediated by cAMP in a Marine Diatom

Hisashi Harada , Kensuke Nakajima , Kunihiro Sakaue , and Yusuke Matsuda *

Department of Bioscience, School of Science and Technology, Kwansei-Gakuin University, 2-1 Gakuen, Sanda, Hyogo, Japan, 669-1337

* Corresponding author; email: yusuke{at}ksc.kwansei.ac.jp.

Marine diatoms are known to be responsible for about a quarter of global primary production and their photosynthesis is sustained by inorganic-carbon concentrating mechanisms (CCM) and/or C4 metabolism. Activities of the CCM are attenuated under enriched [CO2], however, impacts of this factor on primary productivity have so far not been evaluated and the molecular mechanisms of CO2 responses in marine diatoms are unknown. In this study, transgenic cells were generated of the marine diatom Phaeodactylum tricornutum by the introduction of a {beta}-glucuronidase reporter gene under the control of an intrinsic CO2-responsive promoter, which is the sequence between -80 to +61 relative to the transcription-start site of a chloroplastic-carbonic anhydrase gene, ptca1, obtained from P. tricornutum. The activity of the ptca1 promoter was effectively repressed in air-level CO2 by treating cells with a 1.0 mM cAMP analogue, dibutyryl cAMP (dbcAMP) or a cAMP phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Deletion of the intrinsic cAMP-response element from the ptca1 promoter caused a lack of repression of the reporter gene, uidA, even under elevated [CO2] and a null phenotype to the strong repressive effects of dbcAMP and IBMX on the ptca1 promoter. Deletion of the cAMP-response element was also shown to cause derepression of the uidA reporter gene in the dark. These results indicate that cytosolic cAMP level increases under elevated [CO2] and represses the ptca1 promoter. This strongly suggests the participation of cAMP metabolism, presumably at the cytosolic level, in controlling CO2-acquisition systems under the elevated [CO2] at the ocean surface in a marine diatom.




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