title: Oxalate efflux transporter from the brown rot fungus Fomitopsis palustris.
abstract: An oxalate-fermenting brown rot fungus, Fomitopsis palustris, secretes large amounts of oxalic acid during wood decay. Secretion of oxalic acid is indispensable for the degradation of wood cell walls, but almost nothing is known about the transport mechanism by which oxalic acid is secreted from F. palustris hyphal cells. We characterized the mechanism for oxalate transport using membrane vesicles of F. palustris. Oxalate transport in F. palustris was ATP dependent and was strongly inhibited by several inhibitors, such as valinomycin and NH(4)(+), suggesting the presence of a secondary oxalate transporter in this fungus. We then isolated a cDNA, FpOAR (Fomitopsis palustris oxalic acid resistance), from F. palustris by functional screening of yeast transformants with cDNAs grown on oxalic acid-containing plates. FpOAR is predicted to be a membrane protein that possesses six transmembrane domains but shows no similarity with known oxalate transporters. The yeast transformant possessing FpOAR (FpOAR-transformant) acquired resistance to oxalic acid and contained less oxalate than the control transformant. Biochemical analyses using membrane vesicles of the FpOAR-transformant showed that the oxalate transport property of FpOAR was consistent with that observed in membrane vesicles of F. palustris. The quantity of FpOAR transcripts was correlated with increasing oxalic acid accumulation in the culture medium and was induced when exogenous oxalate was added to the medium. These results strongly suggest that FpOAR plays an important role in wood decay by acting as a secondary transporter responsible for secretion of oxalate by F. palustris.
authors.affiliation: Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Watanabe
authors.forename: Nobukazu
authors.initials: N
authors.lastname: Shitan
authors.forename: Shiro
authors.initials: S
authors.lastname: Suzuki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Umezawa
authors.forename: Mikio
authors.initials: M
authors.lastname: Shimada
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Yazaki
authors.forename: Takefumi
authors.initials: T
authors.lastname: Hattori
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D016000:Cluster Analysis; D055453:Coriolaceae / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D004791:Enzyme Inhibitors / Q000378:metabolism; D020869:Gene Expression Profiling; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010070:Oxalates / Q000378:metabolism*; D010802:Phylogeny; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D022142:Secretory Vesicles / Q000201:enzymology; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D014634:Valinomycin / Q000378:metabolism; D014934:Wood / Q000378:metabolism / Q000382:microbiology
chemical_list: D018076:DNA, Complementary; D004271:DNA, Fungal; D004791:Enzyme Inhibitors; D026901:Membrane Transport Proteins; D010070:Oxalates; D000644:Quaternary Ammonium Compounds; D014634:Valinomycin; D000255:Adenosine Triphosphate