Diatom proteomics reveals unique acclimation strategies to mitigate Fe Limitation
Nunn, BL and Faux, JF and Hippman, AA and Maldonado, MT and Harvey, HR and Goodlett, DR and Boyd, PW and Strzepek, RF, Diatom proteomics reveals unique acclimation strategies to mitigate Fe Limitation, PLoS ONE, 8, (10) Article e75653. ISSN 1932-6203 (2013) [Refereed Article]
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Phytoplankton growth rates are limited by the supply of iron (Fe) in approximately one third of the open ocean, with major
implications for carbon dioxide sequestration and carbon (C) biogeochemistry. To date, understanding how alteration of Fe
supply changes phytoplankton physiology has focused on traditional metrics such as growth rate, elemental composition,
and biophysical measurements such as photosynthetic competence (Fv/Fm). Researchers have subsequently employed
transcriptomics to probe relationships between changes in Fe supply and phytoplankton physiology. Recently, studies have
investigated longer-term (i.e. following acclimation) responses of phytoplankton to various Fe conditions. In the present
study, the coastal diatom, Thalassiosira pseudonana, was acclimated (10 generations) to either low or high Fe conditions, i.e.
Fe-limiting and Fe-replete. Quantitative proteomics and a newly developed proteomic profiling technique that identifies
low abundance proteins were employed to examine the full complement of expressed proteins and consequently the
metabolic pathways utilized by the diatom under the two Fe conditions. A total of 1850 proteins were confidently
identified, nearly tripling previous identifications made from differential expression in diatoms. Given sufficient time to
acclimate to Fe limitation, T. pseudonana up-regulates proteins involved in pathways associated with intracellular protein
recycling, thereby decreasing dependence on extracellular nitrogen (N), C and Fe. The relative increase in the abundance of
photorespiration and pentose phosphate pathway proteins reveal novel metabolic shifts, which create substrates that could
support other well-established physiological responses, such as heavily silicified frustules observed for Fe-limited diatoms.
Here, we discovered that proteins and hence pathways observed to be down-regulated in short-term Fe starvation studies
are constitutively expressed when T. pseudonana is acclimated (i.e., nitrate and nitrite transporters, Photosystem II and
Photosystem I complexes). Acclimation of the diatom to the desired Fe conditions and the comprehensive proteomic
approach provides a more robust interpretation of this dynamic proteome than previous studies.