title: Silencing of the Rac1 GTPase MtROP9 in Medicago truncatula stimulates early mycorrhizal and oomycete root colonizations but negatively affects rhizobial infection.
abstract: RAC/ROP proteins (ρ-related GTPases of plants) are plant-specific small G proteins that function as molecular switches within elementary signal transduction pathways, including the regulation of reactive oxygen species (ROS) generation during early microbial infection via the activation of NADPH oxidase homologs of plants termed RBOH (for respiratory burst oxidase homolog). We investigated the role of Medicago truncatula Jemalong A17 small GTPase MtROP9, orthologous to Medicago sativa Rac1, via an RNA interference silencing approach. Composite M. truncatula plants (MtROP9i) whose roots have been transformed by Agrobacterium rhizogenes carrying the RNA interference vector were generated and infected with the symbiotic arbuscular mycorrhiza fungus Glomus intraradices and the rhizobial bacterium Sinorhizobium meliloti as well as with the pathogenic oomycete Aphanomyces euteiches. MtROP9i transgenic lines showed a clear growth-reduced phenotype and revealed neither ROS generation nor MtROP9 and MtRBOH gene expression after microbial infection. Coincidently, antioxidative compounds were not induced in infected MtROP9i roots, as documented by differential proteomics (two-dimensional differential gel electrophoresis). Furthermore, MtROP9 knockdown clearly promoted mycorrhizal and A. euteiches early hyphal root colonization, while rhizobial infection was clearly impaired. Infected MtROP9i roots showed, in part, extremely swollen noninfected root hairs and reduced numbers of deformed nodules. S. meliloti nodulation factor treatments of MtROP9i led to deformed root hairs showing progressed swelling of its upper regions or even of the entire root hair and spontaneous constrictions but reduced branching effects occurring only at swollen root hairs. These results suggest a key role of Rac1 GTPase MtROP9 in ROS-mediated early infection signaling.
authors.affiliation: Leibniz University of Hannover, Institute for Plant Genetics, Department III, Plant Molecular Biology, D-30419 Hannover, Germany.
authors.forename: Leonard Muriithi
authors.initials: LM
authors.lastname: Kiirika
authors.forename: Hannah Friederike
authors.initials: HF
authors.lastname: Bergmann
authors.forename: Christine
authors.initials: C
authors.lastname: Schikowsky
authors.forename: Diana
authors.initials: D
authors.lastname: Wimmer
authors.forename: Joschka
authors.initials: J
authors.lastname: Korte
authors.forename: Udo
authors.initials: U
authors.lastname: Schmitz
authors.forename: Karsten
authors.initials: K
authors.lastname: Niehaus
authors.forename: Frank
authors.initials: F
authors.lastname: Colditz
mesh_terms: D060054:Agrobacterium / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D046913:Medicago truncatula / Q000201:enzymology / Q000235:genetics / Q000382:microbiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000254:growth & development*; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism; D009868:Oomycetes / Q000472:pathogenicity*; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D016897:Respiratory Burst; D053204:Root Nodules, Plant / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D015398:Signal Transduction; D016962:Sinorhizobium meliloti / Q000254:growth & development*; D013559:Symbiosis
chemical_list: D008565:Membrane Proteins; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D019255:NADPH Oxidases; D020558:GTP Phosphohydrolases