Cymodocea nodosa response to simulated CO2-driven ocean acidification: a first insight from global transcriptome profiling

Global climate changes are imposing multiple pressures to marine organisms. The rising atmospheric CO2 concentration is causing substantial changes in ocean physics, chemistry and biology. At least three synergic environmental stressors have been recognized as primary driven by CO2 emissions: ocean warming, oxygen loss and ocean acidification. The effects of CO2-driven ocean acidification on seagrass metabolism remain largely understudied. A few studies have been conducted near submarine volcanic vents, which mimic the future ocean acidification scenarios, allowing researchers to investigate the performance of marine organisms under long-term exposure to high-CO2 levels. Apart from these, some mesocosm-based experiments have investigated growth and physiological responses to high CO2. For this work, we built an outdoor mesocosm facility at the Centre of Marine Sciences’ field station in Algarve, Portugal, to experimentally manipulate CO2 levels and investigate the effects of high-CO2/low pH on seagrass metabolism and underlying molecular mechanisms. Cymodocea nodosa plants were collected in Cadiz Bay at the end of January 2014 and transported to the mesocosm facility. After a one week acclimation period, C. nodosa were either kept under normal (400 ppm) or elevated (1200 ppm) CO2 concentration for 12 days. Water physico-chemical parameters, irradiance, and chlorophyll-fluorescence-derived photosynthetic parameters were monitored on a daily basis. Here we present, for the first time in this species, results obtained using Illumina RNAseq technology and de-novo transcriptome assembly. Using C. nodosa RNAs extracted at the beginning and the end of the experiment, we assembled more than 70 thousands unique transcripts and were able to annotate more than 90% of them using the Annocript pipeline. Differential expression analysis revealed about 500 transcripts significantly differentially regulated between plants kept under control and high-CO2 conditions. Pathways showing largest changes in gene expression included isoprenoid and amino-acid biosynthesis, porphyrin-containing compound metabolism, amine and polyamine biosynthesis, lipid and carbohydrate metabolism. Transcriptome sequencing also significantly increases the molecular resources available for C. nodosa, almost completely absent before this study.