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Characterization of the molecular mechanisms of silicon uptake in coccolithophores.

Published version
Peer-reviewed

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Authors

Ratcliffe, Sarah 
Meyer, Erin M 
Walker, Charlotte E 
Knight, Michael 
McNair, Heather M 

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.

Description

Keywords

Silicon, Phytoplankton, Membrane Transport Proteins, Diatoms, Calcification, Physiologic, Haptophyta

Journal Title

Environ Microbiol

Conference Name

Journal ISSN

1462-2912
1462-2920

Volume Title

Publisher

Wiley
Sponsorship
H2020 European Research Council (ERC‐2011‐StG_20101109, ERC‐ADG‐670390)
National Science Foundation (1638838, 1828053, ECCS‐1542174)
Natural Environment Research Council (NE/N011708/1, NSF‐GEO 1638838)