title: Rhizobium-legume symbiosis shares an exocytotic pathway required for arbuscule formation.
abstract: Endosymbiotic interactions are characterized by the formation of specialized membrane compartments, by the host in which the microbes are hosted, in an intracellular manner. Two well-studied examples, which are of major agricultural and ecological importance, are the widespread arbuscular mycorrhizal symbiosis and the Rhizobium-legume symbiosis. In both symbioses, the specialized host membrane that surrounds the microbes forms a symbiotic interface, which facilitates the exchange of, for example, nutrients in a controlled manner and, therefore, forms the heart of endosymbiosis. Despite their key importance, the molecular and cellular mechanisms underlying the formation of these membrane interfaces are largely unknown. Recent studies strongly suggest that the Rhizobium-legume symbiosis coopted a signaling pathway, including receptor, from the more ancient arbuscular mycorrhizal symbiosis to form a symbiotic interface. Here, we show that two highly homologous exocytotic vesicle-associated membrane proteins (VAMPs) are required for formation of the symbiotic membrane interface in both interactions. Silencing of these Medicago VAMP72 genes has a minor effect on nonsymbiotic plant development and nodule formation. However, it blocks symbiosome as well as arbuscule formation, whereas root colonization by the microbes is not affected. Identification of these VAMP72s as common symbiotic regulators in exocytotic vesicle trafficking suggests that the ancient exocytotic pathway forming the periarbuscular membrane compartment has also been coopted in the Rhizobium-legume symbiosis.
authors.affiliation: Laboratory of Molecular Biology, Department of Plant Sciences, Graduate School Experimental Plant Sciences,  Wageningen University, 6708 PB Wageningen,  The Netherlands.
authors.forename: Sergey
authors.initials: S
authors.lastname: Ivanov
authors.forename: Elena E
authors.initials: EE
authors.lastname: Fedorova
authors.forename: Erik
authors.initials: E
authors.lastname: Limpens
authors.forename: Stephane
authors.initials: S
authors.lastname: De Mita
authors.forename: Andrea
authors.initials: A
authors.lastname: Genre
authors.forename: Paola
authors.initials: P
authors.lastname: Bonfante
authors.forename: Ton
authors.initials: T
authors.lastname: Bisseling
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D007887:Fabaceae / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D020868:Gene Silencing; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D046913:Medicago truncatula / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D038821:Mycorrhizae / Q000378:metabolism*; D010802:Phylogeny; D030821:Plants, Genetically Modified; D032107:Populus / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D050683:R-SNARE Proteins / Q000378:metabolism*; D012231:Rhizobium / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013025:Glycine max / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D050683:R-SNARE Proteins; C570049:VAMP721 protein, Arabidopsis