title: A fungal conserved gene from the basidiomycete Hebeloma cylindrosporum is essential for efficient ectomycorrhiza formation.
abstract: We used Agrobacterium-mediated insertional mutagenesis to identify genes in the ectomycorrhizal fungus Hebeloma cylindrosporum that are essential for efficient mycorrhiza formation. One of the mutants presented a dramatically reduced ability to form ectomycorrhizas when grown in the presence of Pinus pinaster. It failed to form mycorrhizas in the presence of glucose at 0.5 g liter(-1), a condition favorable for mycorrhiza formation by the wild-type strain. However, it formed few mycorrhizas when glucose was replaced by fructose or when glucose concentration was increased to 1 g liter(-1). Scanning electron microscopy examination of these mycorrhizas revealed that this mutant was unable to differentiate true fungal sheath and Hartig net. Molecular analyses showed that the single-copy disrupting T-DNA was integrated 6,884 bp downstream from the start codon, of an open reading frame potentially encoding a 3,096-amino-acid-long protein. This gene, which we named HcMycE1, has orthologs in numerous fungi as well as different other eukaryotic microorganisms. RNAi inactivation of HcMycE1 in the wild-type strain also led to a mycorrhizal defect, demonstrating that the nonmycorrhizal phenotype of the mutant was due to mutagenic T-DNA integration in HcMycE1. In the wild-type strain colonizing P. pinaster roots, HcMycE1 was transiently upregulated before symbiotic structure differentiation. Together with the inability of the mutant to differentiate these structures, this suggests that HcMycE1 plays a crucial role upstream of the fungal sheath and Hartig net differentiation. This study provides the first characterization of a fungal mutant altered in mycorrhizal ability.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Doré
authors.forename: Roland
authors.initials: R
authors.lastname: Marmeisse
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Combier
authors.forename: Gilles
authors.initials: G
authors.lastname: Gay
mesh_terms: D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D055364:Hebeloma / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D025282:Mycelium; D038821:Mycorrhizae / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure; D010641:Phenotype; D010802:Phylogeny; D028223:Pinus / Q000382:microbiology* / Q000648:ultrastructure; D018517:Plant Roots / Q000382:microbiology / Q000648:ultrastructure; D034622:RNA Interference; D013559:Symbiosis
chemical_list: D005656:Fungal Proteins