Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler is a cosmopolitan coccolithophore species that forms massive blooms in low phosphorus seawater, partly due to its ability to utilize organic phosphate via extracellular alkaline phosphatase (AP). A novel AP gene, ehap1, was identified from the strain CCMP374. In this study, we examined the expression of ehap1 in various E. huxleyi strains and its genetic diversity in those strains and field populations. Two EHAP1 proteins (EHAP1a, 75 kDa and EHAP1b, 110 kDa) with virtually identical sequence were expressed under P limitation in all strains except one; a third protein (EHAP1c, 115 kDa) was expressed in a few strains. The correlation between AP activity and protein abundance suggests that EHAP1b is inactive and probably the precursor of EHAP1a. The transcript of ehap1 was induced by P depletion in all strains. The ehap1 gene sequence is highly conserved in these strains and field populations with <3% nucleic acid substitution. Most of the ehap1 sequences from one site in the English Channel and three sites in the Gulf of Alaska were essentially identical to one another. No EHAP1-like protein can be detected in other phytoplankton species tested via Western blot analysis. The rapid induction and high activity of EHAP1 in E. huxleyi suggest that it plays a significant role in P regeneration in the oligotrophic ocean where E. huxleyi is abundant. The EHAP1 antibody and gene-specific primers are well suited to study the dynamics of P limitation in field populations of E. huxleyi.
All Science Journal Classification (ASJC) codes
- Aquatic Science
- Plant Science