Carbon allocation in ectomycorrhizas: identification and expression analysis of an Amanita muscaria monosaccharide transporter.
Ectomycorrhizas are formed between certain soil fungi and fine roots of predominantly woody plants. An important feature of this symbiosis is the supply of plant-derived carbohydrates to the fungus. As a first step toward a better understanding of the molecular basis of this process, we cloned a monosaccharide transporter from the ectomycorrhizal fungus Amanita muscaria. Degenerate oligonucleotide primers were designed to match conserved regions from known fungal sugar transporters. A cDNA fragment of the transporter was obtained from mycorrhizal mRNA by reverse transcription-polymerase chain reaction. This fragment was used to identify a clone (AmMst1) encoding the entire monosaccharide transporter in a Picea abies/A. muscaria mycorrhizal cDNA library. The cDNA codes for an open reading frame of 520 amino acids, showing best homology to a Neurospora crassa monosaccharide transporter. The function of AmMST1 as monosaccharide transporter was confirmed by heterologous expression of the cDNA in a Schizosaccharomyces pombe mutant lacking a monosaccharide uptake system. AmMst1 was constitutively expressed in fungal hyphae under all growth conditions. Nevertheless, in mycorrhizas as well as in hyphae grown at monosaccharide concentrations above 5 mM, the amount of AmMst1 transcript increased fourfold. We therefore suggest that AmMst1 is upregulated in ectomycorrhizas by a monosaccharide-controlled mechanism.
Nehls
U
U
Universität Tübingen, Germany. uwe.nehls@uni-tuebingen.de
Wiese
J
J
Guttenberger
M
M
Hampp
R
R
D000545:Amanita / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D016384:Consensus Sequence; D017124:Conserved Sequence; D017931:DNA Primers; D005656:Fungal Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D015723:Gene Library; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D009492:Neurospora crassa / Q000235:genetics; D016366:Open Reading Frames; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis; D014197:Trees / Q000382:microbiology
D017931:DNA Primers; D005656:Fungal Proteins; C111094:MST-1 protein, Amanita muscaria; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins