Transcriptional and Translational Regulation of Nitrate Transporter Genes in a Marine Diatom Skeletonema tropicum

As one of essential nutrients, nitrogen is a limiting factor for phytoplankton growth in the ocean. Among the inorganic nitrogen sources, nitrate is considered as the preferred from of nitrogen for diatoms. Due to low nitrate levels in marine environment, diatoms require active transporters to take up nitrate across cell membranes, and nitrate transporters (NRT2) are thought to be the major membrane proteins responsible for nitrate uptake in diatoms. Therefore, understanding the regulation of nitrate transporters is helpful to explore the nitrate uptake mechanism in diatoms. In this study, gene and protein expression of 3 forms of nitrate transporter was monitored under various nitrogen status in a diatom Skeletoneema tropicum (Strain Kao). Cells were grown under different nitrogen status including nitrate-sufficient, ammonium-sufficient and nitrogen-limited conditions. To monitor the gene expression of each form of Nrt2, quantitative reverse transcription polymerase chain reaction was used. Our results indicated that Nrt2.1 increased to the highest transcript level under nitrate-limited condition, Nrt2.2 increased to higher transcript level only under nitrate-sufficient condition, and Nrt2.3 is more like a constitutive gene. As the protein expression, the differential expression profiles of each NRT2 were determined by mass spectrometer analysis. Comparing the gene and protein expression profiles of each form of nitrate transporters would provide more information to understand how diatoms regulate the nitrate uptake to cope with environmental changes.