Abstract
The transcription of chloroplastic β-carbonic anhydrase gene (ptca1) in the marine diatom Phaeodactylum tricornutum is known to respond to environmental CO2 concentration mediated by a second messenger cAMP. Our recent studies revealed that the promoter of the ptca1 has three tandemly-aligned cis-elements, CO2/cAMP responsive elements (CCRE1-3), and alternative combinations of CCRE1/3 or CCRE2 are essential to repress the ptca1 in response to CO2 increase. Our preliminary results also suggested the existence of cAMP independent pathways for CO2 signal transduction. In this study, we screened putative CO2-responsive genes in P. tricornutum by semi qRT-PCR, and obtained three candidate genes. We obtained for these candidate genes putative promoter regions. In order to evaluate promoter activities, those promoter regions were fused with GUS reporter gene, uidA and introduced into P. tricornutum cells. Results of GUS reporter assay demonstrated that the promoter of one of the candidate genes, ptsbt4 showed cAMP dependent CO2 response. However deletion assays of ptsbt4 promoter indicated that regions required of CO2 or cAMP response were independent.
