1. Darmstadt University of Technology, Institute of Botany, Schnittspahnstrasse 10, 64287 Darmstadt, Germany
2. University of Bonn, IZMB, NWG Transport in Mycorrhiza, Kirschallee 1, 53115 Bonn, Germany
3. Present address: Bereich Genetik, Department Biologie I, Maria-Ward-Strae 1a, 80638 München, Germany.

Correspondence to: Arthur Schüler^1,3 Correspondence and requests for materials should be addressed to A.S. (Email: arthur.schuessler@lrz.uni-muenchen.de). Sequences are deposited at EMBL Data Bank with the accession numbers AM231332 (GpMST1cDNAclonepHM13-C6.1) and AM231333 (GpMST1gDNAclonepDC-C6). Plasmids and clones are available on request.

Abstract

The symbiotic relationships between mycorrhizal fungi and plants have an enormous impact on terrestrial ecosystems¹. Most common are the arbuscular mycorrhizas, formed by fungi belonging to the phylum Glomeromycota². Arbuscular mycorrhizal fungi facilitate the uptake of soil nutrients by plants³ and in exchange obtain carbohydrates, thus representing a large sink⁴ for atmospheric plant-fixed CO₂. However, how carbohydrates are transported through the symbiotic interface is still unknown. Here we report the characterization of the first known glomeromycotan monosaccharide transporter, GpMST1, by exploiting the unique symbiosis of a glomeromycotan fungus (Geosiphon pyriformis) with cyanobacteria⁵. The GpMST1 gene has a very low GC content and contains six introns with unusual boundaries. GpMST1 possesses twelve predicted transmembrane domains and functions as a proton co-transporter with highest affinity for glucose, then mannose, galactose and fructose. It belongs to an as yet uncharacterized phylogenetic monosaccharide transporter clade. This initial characterization of a new transporter family involved in fungal symbiosis will lead to a better understanding of carbon flows in terrestrial environments.

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