Abstract
In the marine diatom Phaeodactylum tricornutum, cAMP functions as second messenger for the increment of [CO2] and represses transcription of the carbonic anhydrase gene, ptca1, under high CO2 condition. In this study, cAMP-phosphodiesterase (cAMP-PDE), was searched and characterized in P. tricornutum. cAMP-PDE activity in diatom lysate was measured. As a result, cAMP-PDE activity was detected in both soluble and insoluble fractions of diatom lysates. Candidate genes of cAMP-PDE were searched from diatom genome database, and 10 membrane-bound and 2 soluble type genes were found. Eight membrane-bound type genes were cloned and, semiquantitative RT-PCR was carried out on mRNAs obtained from cells grown in air and high CO2. Many of candidate genes were upregulated in high CO2. Interestingly, all 8 genes had primary structures, which possess activity domains of either adenylyl or guanylyl cyclases (NC) and PDE in the single open reading frame. To elucidate relationships between two component systems of NC/PDE and cAMP signal transduction systems, candidate genes were overexpressed in diatom cells.
