title: A family of diatom-like silicon transporters in the siliceous loricate choanoflagellates.
abstract: Biosilicification is widespread across the eukaryotes and requires concentration of silicon in intracellular vesicles. Knowledge of the molecular mechanisms underlying this process remains limited, with unrelated silicon-transporting proteins found in the eukaryotic clades previously studied. Here, we report the identification of silicon transporter (SIT)-type genes from the siliceous loricate choanoflagellates Stephanoeca diplocostata and Diaphanoeca grandis. Until now, the SIT gene family has been identified only in diatoms and other siliceous stramenopiles, which are distantly related to choanoflagellates among the eukaryotes. This is the first evidence of similarity between SITs from different eukaryotic supergroups. Phylogenetic analysis indicates that choanoflagellate and stramenopile SITs form distinct monophyletic groups. The absence of putative SIT genes in any other eukaryotic groups, including non-siliceous choanoflagellates, leads us to propose that SIT genes underwent a lateral gene transfer event between stramenopiles and loricate choanoflagellates. We suggest that the incorporation of a foreign SIT gene into the stramenopile or choanoflagellate genome resulted in a major metabolic change: the acquisition of biomineralized silica structures. This hypothesis implies that biosilicification has evolved multiple times independently in the eukaryotes, and paves the way for a better understanding of the biochemical basis of silicon transport through identification of conserved sequence motifs.
authors: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK. am543@cam.ac.uk
authors: Alan O
authors: AO
authors: Marron
authors: Mark J
authors: MJ
authors: Alston
authors: Darren
authors: D
authors: Heavens
authors: Michael
authors: M
authors: Akam
authors: Mario
authors: M
authors: Caccamo
authors: Peter W H
authors: PW
authors: Holland
authors: Giselle
authors: G
authors: Walker
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D056897:Choanoflagellata / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence; D017377:Diatoms / Q000378:metabolism; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D012825:Silicon / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D012825:Silicon