title: A versatile monosaccharide transporter that operates in the arbuscular mycorrhizal fungus Glomus sp is crucial for the symbiotic relationship with plants.
abstract: For more than 400 million years, plants have maintained a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi. This evolutionary success can be traced to the role of these fungi in providing plants with mineral nutrients, particularly phosphate. In return, photosynthates are given to the fungus, which support its obligate biotrophic lifestyle. Although the mechanisms involved in phosphate transfer have been extensively studied, less is known about the reciprocal transfer of carbon. Here, we present the high-affinity Monosaccharide Transporter2 (MST2) from Glomus sp with a broad substrate spectrum that functions at several symbiotic root locations. Plant cell wall sugars can efficiently outcompete the Glc uptake capacity of MST2, suggesting they can serve as alternative carbon sources. MST2 expression closely correlates with that of the mycorrhiza-specific Phosphate Transporter4 (PT4). Furthermore, reduction of MST2 expression using host-induced gene silencing resulted in impaired mycorrhiza formation, malformed arbuscules, and reduced PT4 expression. These findings highlight the symbiotic role of MST2 and support the hypothesis that the exchange of carbon for phosphate is tightly linked. Unexpectedly, we found that the external mycelium of AM fungi is able to take up sugars in a proton-dependent manner. These results imply that the sugar uptake system operating in this symbiosis is more complex than previously anticipated.
authors.affiliation: Plant-Microbial Interactions Group, Karlsruhe Institute of Technology, Hertzstrasse 16, D-76187 Karlsruhe, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Helber
authors.forename: Kathrin
authors.initials: K
authors.lastname: Wippel
authors.forename: Norbert
authors.initials: N
authors.lastname: Sauer
authors.forename: Sara
authors.initials: S
authors.lastname: Schaarschmidt
authors.forename: Bettina
authors.initials: B
authors.lastname: Hause
authors.forename: Natalia
authors.initials: N
authors.lastname: Requena
mesh_terms: D001483:Base Sequence; D001692:Biological Transport; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015723:Gene Library; D055137:Glomeromycota / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D005947:Glucose / Q000378:metabolism; D006706:Homeostasis; D046913:Medicago truncatula / Q000382:microbiology* / Q000502:physiology; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D025282:Mycelium / Q000378:metabolism; D038821:Mycorrhizae / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D010710:Phosphates / Q000378:metabolism; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology; D011522:Protons; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D013379:Substrate Specificity; D013559:Symbiosis / Q000502:physiology*; D014994:Xylose / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D009004:Monosaccharide Transport Proteins; D010710:Phosphates; D011522:Protons; D014994:Xylose; D005947:Glucose