Abstract
Expression of PtCA1, a chloroplastic carbonic anhydrase in the marine diatom Phaeodactylum tricornutum, is regulated by ambient CO2 concentration and light at the transcriptional level, that is down regulated under high CO2 or dark conditions. In previous studies, 3 critical CO2/cAMP-response elements (CCRE1-3) were identified at the promoter region of ptca1 (Pptca1) and it was reveled that these elements are under control of cAMP as second messenger. However, light-response mechanisms of Pptca1 in not clarified yet. In this study, light-response elements in Pptca1 were determined. GUS reporter assay using one base replaced constructs of CCRE2 and 3 and their adjacent sequences, it was shown that light-response element exactly corresponded to CCRE2 and 3. We tested the light-response element of CCRE1 and found that CCRE1 is also responsible for light-response of the Pptca1. These results indicated that light-response elements are identical to CO2-response elements, CCRE1-3, in Pptca1. Further analysis of light-response of Pptca1 using dibutylyl cAMP (dbcAMP), an analogue of cAMP, demonstrated that light signal is also transduced by cAMP as a second messenger.
