Expression in a stressful situation: Analysis of the marine diatom Thalassiosira under phosphorus limitation, FE limitation and colimitation

Diatoms are unicellular eukaryotic organisms that provide large amounts of primary productivity to the oceans and play a dominant role in the global carbon cycle. Phosphorus (P) and iron (Fe) are critical nutrients in diatom growth and primary productivity. Low concentrations cause reduced growth rate and reduced maximum biomass decreasing diatom ability to form blooms and fix carbon from the atmosphere. Using whole transcriptome sequencing we were able to take an unbiased look at the global response of T. pseudonana to phosphate limitation. We identified changes in cellular P allocation, increased P transport, a switch to utilization of dissolved organic P and a remodeling of the cell surface. The results highlight novel aspects of the diatom P stress response. A putative phosphate transporter was the most highly expressed gene under P limitation. qPCR was used to elucidate the change in expression over time under replete and P limited conditions. Increasing expression with decreasing [P] was identified in T pseudonana and Ditylum brightwellii. No response was seen in expression to N, Si, or Fe limitation indicating that this phosphate transporter has the potential to serve as a molecular indicator of P stress in the environment.