Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient-rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift-up, is characterized by increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here, we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co-expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment.
|emi14361-sup-0001-appendixS1.docxWord 2007 document , 1.8 MB||Appendix S1. Supporting Information|
|emi14361-sup-0002-appendixS2.xlsxExcel 2007 spreadsheet , 56.7 KB||Data Set S1. Uniquely overrepresented genes displayed in Fig. 4C for each taxonomic group.|
|emi14361-sup-0003-appendixS3.xlsxExcel 2007 spreadsheet , 22.6 KB||Data Set S2. Chaetoceros and Pseudo-nitzschia genes that show significantly opposing expression to other diatoms.|
|emi14361-sup-0004-appendixS4.xlsxExcel 2007 spreadsheet , 50.5 KB||Data Set S3. Genes of unknown function significantly expressed in our study and with positive fold-changes in similar studies on T. pseudonana (tps) and P. tricornutum (pti). The study with T. pseudonana shows genes with positive fold-changes during exponential growth and light after three days. The dataset with P. tricornutum shows genes expressed after 48 hours of darkness followed by 24 hours of re-exposure to light.|
Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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