title: Phylogenetic evidence for a fusion of archaeal and bacterial SemiSWEETs to form eukaryotic SWEETs and identification of SWEET hexose transporters in the amphibian chytrid pathogen Batrachochytrium dendrobatidis.
abstract: SWEETs represent a new class of sugar transporters first described in plants, animals, and humans and later in prokaryotes. Plant SWEETs play key roles in phloem loading, seed filling, and nectar secretion, whereas the role of archaeal, bacterial, and animal transporters remains elusive. Structural analyses show that eukaryotic SWEETs are composed of 2 triple-helix bundles (THBs) fused via an inversion linker helix, whereas prokaryotic SemiSWEETs contain only a single THB and require homodimerization to form transport pores. This study indicates that SWEETs retained sugar transport activity in all kingdoms of life, and that SemiSWEETs are likely their ancestral units. Fusion of oligomeric subunits into single polypeptides during evolution of eukaryotes is commonly found for transporters. Phylogenetic analyses indicate that THBs of eukaryotic SWEETs may not have evolved by tandem duplication of an open reading frame, but rather originated by fusion between an archaeal and a bacterial SemiSWEET, which potentially explains the asymmetry of eukaryotic SWEETs. Moreover, despite the ancient ancestry, SWEETs had not been identified in fungi or oomycetes. Here, we report the identification of SWEETs in oomycetes as well as SWEETs and a potential SemiSWEET in primitive fungi. BdSWEET1 and BdSWEET2 from Batrachochytrium dendrobatidis, a nonhyphal zoosporic fungus that causes global decline in amphibians, showed glucose and fructose transport activities.-Hu, Y.-B., Sosso, D., Qu, X.-Q., Chen, L.-Q., Ma, L., Chermak, D., Zhang, D.-C., Frommer, W. B. Phylogenetic evidence for a fusion of archaeal and bacterial SemiSWEETs to form eukaryotic SWEETs and identification of SWEET hexose transporters in the amphibian chytrid pathogen Batrachochytrium dendrobatidis.
authors.affiliation: College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China; Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA; huyb@njau.edu.cn.
authors.forename: Yi-Bing
authors.initials: YB
authors.lastname: Hu
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA.
authors.forename: Davide
authors.initials: D
authors.lastname: Sosso
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA.
authors.forename: Xiao-Qing
authors.initials: XQ
authors.lastname: Qu
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA; Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA; Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors.forename: Li-Qing
authors.initials: LQ
authors.lastname: Chen
authors.affiliation: College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China.
authors.forename: Lai
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA.
authors.forename: Diane
authors.initials: D
authors.lastname: Chermak
authors.affiliation: Biotechnology Research Center, China Three Gorges University, Yichang, China.
authors.forename: De-Chun
authors.initials: DC
authors.lastname: Zhang
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA; wfrommer@stanford.edu.
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D000818:Animals; D001692:Biological Transport; D008411:Chytridiomycota / Q000302:isolation & purification / Q000472:pathogenicity*; D056890:Eukaryota / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins
keywords: LECA; gene conversion; oomycete; sugar transport; transporter evolution