Response of Emiliania huxleyi to a high CO2 world: assessing the extent of genetic diversity in the pattern of gene expression

点击翻译按钮获取中文摘要

Emiliania huxleyi is a fast growing 'coccolithophorid' phytoplankton species that forms calcium carbonate (CaCO3) plates on the outside of its cells. In the modern ocean, E. huxleyi is one of the most abundant 'bloom forming' phytoplankton species and consequently plays a major role in removal (export) of both carbon and alkalinity from surface waters. Substantial laboratory research has previously examined how environmental factors, such as light, temperature and nutrients, interact to affect the growth and calcification of E. huxleyi. However, the major factor that is critical to the balance between growth and calcification for E. huxleyi is the pH of seawater. With this in mind, global attention has focused upon how E. huxleyi will respond to the decrease in ocean pH (ocean acidification) that has been predicted as a result of elevated atmospheric CO2 concentrations. Recent research has demonstrated that an increase in atmospheric CO2 directly reduces calcification by E. huxleyi; in turn, the efficiency with which this organism can export material from the surface ocean will likely decrease. Despite such progress, the last report of the Intergovernmental Panel on Climate Change highlighted that 'the impact of ocean acidification on marine biota especially for organisms achieving bio-calcification remains a key uncertainty'. Of major concern is that the species of E. huxleyi is comprised of an 'untold number' of genetic variants and independent experiments (including CO2 perturbations) do not always examine environmentally-driven characteristics for the same variant. Results from our laboratory support this statement: two variants exhibited very different modes of acclimation to perturbations of light and CO2 conditions for growth. Changes in gene expression are the bases by which these organisms appear to respond to environmental change, a fact that has led to suggestions that genomics and transcriptomics should be applied to increase our knowledge of ocean biogeochemistry. However, a huge conceptual gap still exists between molecular genetics and biogeochemistry: geochemists need generalisations that can be applied to the entire ocean over long time periods; biologists focus on what makes an organism unique. Key to bridging the current gap between molecular biology and biogeochemistry is to examine the extent with which variability in gene expression is due to genetic differences amongst isolates versus general responses to environmental forcing. This study builds immediately upon previous NERC grants held by the investigators by addressing how gene expression responds to changes of ocean pH for genetic variants of E. huxleyi. We propose a programme of collaborative research involving the University of Essex and Marine Biological Association of the UK under the SOFI call 'Coccolithophore gene expression profiles in chemostat culture and microarray analysis' (WP 2.8, 2.9) within priority topic area marine biogeochemical cycles. 'pH-stat' technology developed in our laboratory will be used to grow four E. huxleyi genetic variants at two pH conditions (present day versus that predicted beyond the year 2100). Microarray-based molecular signals in response to the different pH conditions within and between variants will be compared but also analysed alongside physiological signals (photosynthesis and calcificiation). Work proposed here will establish a core link between two research centers with an excellent track record investigating E. huxleyi biology, the University of Essex and the UK's Marine Biological Association, which is an Ocean 2025 Centre.