Alkaline Phosphatase Gene Sequence And Transcriptional Regulation By Phosphate Limitation In Amphidinium Carterae (Dinophyceae)(1).

Alkaline phosphatase (AP) in phytoplankton facilitates the utilization of dissolved organic phosphorus (DOP) when the dissolved inorganic phosphorus (DIP) is limited in the environment. The AP gene sequence and its expression under DIP limitation has not been studied in dinoflagellates. In this study, we isolated the full-length cDNA of AP from the toxic dinoflagellate Amphidinium carterae Hulburt (2,112 bp, named as acaap). The deduced amino acid sequence of acaap (ACAAP, 704 amino acid residues) was identified as a membrane-associated protein, in agreement with the dominantly cell surface localization of the AP activity shown with enzyme-labeled fluorescence (ELF) labeling. ACAAP shares sequence similarity in the key domains with APs from diatoms, proteobacteria, and cyanobacteria. In accordance, phylogenetic reconstruction showed clustering of ACAAP with counterparts in those organisms, although branches were long as a result of the generally high variability of the gene sequence. The expression levels of acaap were studied for A. carterae cultured in media with different phosphate concentrations using quantitative reverse-transcription PCR (RT-qPCR) method. The result showed that the transcription level of acaap was elevated in the DIP-depleted cultures relative to the DIP-replete cultures and repressed upon resupply of DIP. The transcription level of acaap exhibited a positive correlation with AP enzyme activity. Taken together, these results demonstrate that AP activity and gene expression are regulated by the availability of DIP in A. carterae, suggesting that AP expression is a promising indicator of DIP stress in this and possibly other species of dinoflagellates.