Sequence Diversity of Ammonium Transporter Genes in Cultured and Natural Species of Marine Phytoplankton

Abstract

The sequence database of ammonium transporter (Amt1) genes in eukaryotic phytoplankton was expanded by obtaining new sequences from cultured strains and natural populations collected in the East China Sea (ECS). From unialgal cultures, 6 new Amt1 sequences belonging to the Bacillariophyceae, Dinophyceae, and Prasinophyceae were obtained. A phylogenetic analysis revealed that AMT1s of higher plants were most closely related to those in green algae. In addition, haptophyte and diatom AMT1s formed distinct monophyletic clades. Diatom AMT1s were further divided into 3 orthologous subclasses, and active gene duplications were observed in subclass III. As for mixed-species sequencing using ECS samples, 78 sequences homologous to Amt1 were retrieved, and diatom AMT1s were the dominant group. Our results indicated that eukaryotic phytoplankton Amt1 genes can be cloned at both the DNA and the RNA levels in marine environments, and this information on Amt1 diversity will be useful for quantifying Amt1 expression in the ocean.