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Characterization of the molecular mechanisms of silicon uptake in coccolithophores |
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| Authors: | Sarah Ratcliffe Erin M. Meyer Charlotte E. Walker Michael Knight Heather M. McNair Paul G. Matson Debora Iglesias-Rodriguez Mark Brzezinski Gerald Langer Aleksey Sadekov Mervyn Greaves Colin Brownlee Paul Curnow Alison R. Taylor Glen L. Wheeler |
| Affiliation: | 1. School of Biochemistry, University of Bristol, Bristol, UK;2. Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, USA;3. Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, UK;4. School of Ocean and Earth Science, University of Southampton, Southampton, UK;5. Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA;6. Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA;7. Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA;8. Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA;9. ARC Centre of Excellence for Coral Reef Studies, Ocean Graduate School, University of Western Australia, Crawley, Western Australia, Australia;10. The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge, UK |
| Abstract: | Coccolithophores are an important group of calcifying marine phytoplankton. Although coccolithophores are not silicified, some species exhibit a requirement for Si in the calcification process. These species also possess a novel protein (SITL) that resembles the SIT family of Si transporters found in diatoms. However, the nature of Si transport in coccolithophores is not yet known, making it difficult to determine the wider role of Si in coccolithophore biology. Here, we show that coccolithophore SITLs act as Na+-coupled Si transporters when expressed in heterologous systems and exhibit similar characteristics to diatom SITs. We find that CbSITL from Coccolithus braarudii is transcriptionally regulated by Si availability and is expressed in environmental coccolithophore populations. However, the Si requirement of C. braarudii and other coccolithophores is very low, with transport rates of exogenous Si below the level of detection in sensitive assays of Si transport. As coccoliths contain only low levels of Si, we propose that Si acts to support the calcification process, rather than forming a structural component of the coccolith itself. Si is therefore acting as a micronutrient in coccolithophores and natural populations are only likely to experience Si limitation in circumstances where dissolved silicon (DSi) is depleted to extreme levels. |
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