title: The Evolution of Silicon Transport in Eukaryotes.
abstract: Biosilicification (the formation of biological structures from silica) occurs in diverse eukaryotic lineages, plays a major role in global biogeochemical cycles, and has significant biotechnological applications. Silicon (Si) uptake is crucial for biosilicification, yet the evolutionary history of the transporters involved remains poorly known. Recent evidence suggests that the SIT family of Si transporters, initially identified in diatoms, may be widely distributed, with an extended family of related transporters (SIT-Ls) present in some nonsilicified organisms. Here, we identify SITs and SIT-Ls in a range of eukaryotes, including major silicified lineages (radiolarians and chrysophytes) and also bacterial SIT-Ls. Our evidence suggests that the symmetrical 10-transmembrane-domain SIT structure has independently evolved multiple times via duplication and fusion of 5-transmembrane-domain SIT-Ls. We also identify a second gene family, similar to the active Si transporter Lsi2, that is broadly distributed amongst siliceous and nonsiliceous eukaryotes. Our analyses resolve a distinct group of Lsi2-like genes, including plant and diatom Si-responsive genes, and sequences unique to siliceous sponges and choanoflagellates. The SIT/SIT-L and Lsi2 transporter families likely contribute to biosilicification in diverse lineages, indicating an ancient role for Si transport in eukaryotes. We propose that these Si transporters may have arisen initially to prevent Si toxicity in the high Si Precambrian oceans, with subsequent biologically induced reductions in Si concentrations of Phanerozoic seas leading to widespread losses of SIT, SIT-L, and Lsi2-like genes in diverse lineages. Thus, the origin and diversification of two independent Si transporter families both drove and were driven by ancient ocean Si levels.
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge, United Kingdom am543@cam.ac.uk.|Department of Zoology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Alan O
authors.initials: AO
authors.lastname: Marron
authors.affiliation: School of Biochemistry, Biomedical Sciences Building, University of Bristol, University Walk, Bristol, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Ratcliffe
authors.affiliation: Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, Devon, United Kingdom.
authors.forename: Glen L
authors.initials: GL
authors.lastname: Wheeler
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Goldstein
authors.affiliation: Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California, Berkeley, CA.
authors.forename: Nicole
authors.initials: N
authors.lastname: King
authors.affiliation: CNRS, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, Roscoff, France.|Sorbonne Universités, Université Pierre et Marie Curie (UPMC) Paris 06, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, Roscoff, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Not
authors.affiliation: CNRS, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, Roscoff, France.|Sorbonne Universités, Université Pierre et Marie Curie (UPMC) Paris 06, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, Roscoff, France.
authors.forename: Colomban
authors.initials: C
authors.lastname: de Vargas
authors.affiliation: Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California, Berkeley, CA.|CNRS, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, Roscoff, France.|Sorbonne Universités, Université Pierre et Marie Curie (UPMC) Paris 06, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, Roscoff, France.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Richter
mesh_terms: D000595:Amino Acid Sequence; D005075:Biological Evolution; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D056897:Choanoflagellata / Q000378:metabolism; D017377:Diatoms / Q000378:metabolism; D056890:Eukaryota / Q000378:metabolism*; D019143:Evolution, Molecular; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012825:Silicon / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D012825:Silicon
keywords: Lsi2; SIT; convergent evolution; eukaryotes; silicon; transporter.