title: A secreted effector protein of Laccaria bicolor is required for symbiosis development.
abstract: Soil-borne mutualistic fungi, such as the ectomycorrhizal fungi, have helped shape forest communities worldwide over the last 180 million years through a mutualistic relationship with tree roots in which the fungal partner provides a large array of nutrients to the plant host in return for photosynthetically derived sugars. This exchange is essential for continued growth and productivity of forest trees, especially in nutrient-poor soils. To date, the signals from the two partners that mediate this symbiosis have remained uncharacterized. Here we demonstrate that MYCORRHIZAL iNDUCED SMALL SECRETED PROTEIN 7 (MiSSP7), the most highly symbiosis-upregulated gene from the ectomycorrhizal fungus Laccaria bicolor, encodes an effector protein indispensible for the establishment of mutualism. MiSSP7 is secreted by the fungus upon receipt of diffusible signals from plant roots, imported into the plant cell via phosphatidylinositol 3-phosphate-mediated endocytosis, and targeted to the plant nucleus where it alters the transcriptome of the plant cell. L. bicolor transformants with reduced expression of MiSSP7 do not enter into symbiosis with poplar roots. MiSSP7 resembles effectors of pathogenic fungi, nematodes, and bacteria that are similarly targeted to the plant nucleus to promote colonization of the plant tissues and thus can be considered a mutualism effector.
authors.affiliation: UMR INRA/UHP 1136, Interactions Arbres/Micro-organismes, Centre INRA de Nancy, 54280 Champenoux, France.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Plett
authors.forename: Minna
authors.initials: M
authors.lastname: Kemppainen
authors.forename: Shiv D
authors.initials: SD
authors.lastname: Kale
authors.forename: Annegret
authors.initials: A
authors.lastname: Kohler
authors.forename: Valérie
authors.initials: V
authors.lastname: Legué
authors.forename: Annick
authors.initials: A
authors.lastname: Brun
authors.forename: Brett M
authors.initials: BM
authors.lastname: Tyler
authors.forename: Alejandro G
authors.initials: AG
authors.lastname: Pardo
authors.forename: Francis
authors.initials: F
authors.lastname: Martin
mesh_terms: D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D016681:Genome, Fungal; D055399:Laccaria / Q000737:chemistry / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D038821:Mycorrhizae / Q000235:genetics / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000382:microbiology; D032107:Populus / Q000382:microbiology; D021381:Protein Transport; D015398:Signal Transduction; D013559:Symbiosis; D059467:Transcriptome
chemical_list: D005656:Fungal Proteins; D018129:Phosphatidylinositol Phosphates; C055525:phosphatidylinositol 3-phosphate