Legume-rhizobia interaction; from simple to complex associations Simona Radutoiu Aarhus University, Department of Molecular Biology and Genetics
Nitrogen-fixing symbiosis in root nodules
Nitrogen-fixing symbiosis in root nodules
Nitrogen-fixing symbiosis in root nodules allows legumes to grow on nitrogen poor soils
Legumes select the nodule-infecting rhizobia not on the basis of their nitrogen-fixing ability H 2 C Nod factor (LCO) O H O O H O O C N C H 3 N H 2 O C C H 2 O H O C H 2 O H O O C N H C H 3 O 3 H 3 C C O H 3 C O O H H O O H 2 C O O H N H O H O C C H 3 O Nodule and Infection thread formation ( H 2 C ) 8 C H C H ( H 2 C ) 5 C H 3 NFR1/NFR5 Mesorhizobium lotilacz infection of nodule in Lotus japonicus
The plant root symbioses Root symbionts Arbuscular mycorrhizal (AM) fungi Nitrogen-fixing bacteria (Rhizobia) Philippot et al. 2013, Nature Reviews Microbiology
M. loti R7A GFP + KAW12 DsRed Endophytes can use the M.loti-induced infection threads to infect the nodule Zgadzaj et al., 2015
M. loti exou -GFP M. loti exou-gfp + Kaw12-DsRed 87 of 3653 nodules (2.4%) 510 of 3588 nodules (14%)*** Kaw12 endophyte promotes nodule infection by the less efficient, but nitrogen fixing M.loti exou
Nitrogen-fixing symbiosis in root nodules allows legumes to grow on nitrogen poor soils
REDUCTIONIST APPROACH Lotus japonicus Mesorhizobium loti (GENERALIST) APPROACH Lotus japonicus soil microbiota
nodule rhizosphere soil root Distinct bacterial communities assemble at the Lotus japonicus root-soil interface Zgadzaj & Garrido-Oter, PNAS 2016
12 OTUs enriched in nodules of which 7 OTUs- Rhizobiales 6 OTUs - Mesorhizobium Nodules host a highly selective bacterial community Zgadzaj & Garrido-Oter, PNAS 2016
Is nitrogen-fixing symbiosis influencing the associated microbiota? WT lhk1-1 nfr5-2 nin2 wt nfr1/nfr5 Zgadzaj & Garrido-Oter, PNAS 2016
Actinobacteridae, Rhodospirilalles, Sphingobacteriales and Xanthomonadales Burkholderiales Flavobacteriales, Myxococcales, Pseudomonadales, and Sphingomonadales Differentiation of root microbiota across multiple bacterial orders is affected Zgadzaj & Garrido-Oter, PNAS 2016
Rhizobiales Enrichment of Rhizobiales in root and rhizosphere depends on the symbiotic pathway
Native soil Native soil + 10mM KNO3 Nitrogen-fixing symbiosis promotes association with specific soil bacteria that promote plant growth
Nitrogen-fixing symbiosis in root nodules has major consequences for interactions in the microbial communities Soil
Nitrogen-fixing symbiosis in root nodules has major consequences for interactions in the microbial communities Symbiosis
? Test conditions Soil conditions
REDUCTIONIST APPROACH Lotus japonicus Mesorhizobium loti (GENERALIST) APPROACH Lotus japonicus soil microbiota
CARB Centre Anna Malolepszy Simon Kelly Christina Grossmann Niels Sandal Mick Blaise Kasper Andersen Stig Andersen Yosuke Umehara Keisuke Yokota Acknowledgments Paul Schulze-Lefert, MPI, Germany Rafal Zgadzaj Ruben Garrido-Oter Clive Ronson- Otago University, New Zealand Euan James- James Hutton Institute, UK
E to K Chitinase E 159 to K Chitinase WT An enzymatically active Chitinase is required for a functional root-nodule symbiosis
chitinase mutants: no signs of plant defense reaction chitinase mutants: no transcriptional activation of defense genes nm acetylene/root/hour 0,2 0,15 0,1 0,05 0 Mutants at Sym43 locus are defective for nitrogen fixation
WT WT WT sym4 3 sym4 3 sym4 3 R7A R7AΔnolL R7AΔnodZ M.loti Wt nodz noll Wt sym43 Wild-type- Gifu chitinase mutants are rescued by M.loti noll or nodz
REDUCTIONIST APPROACH Lotus japonicus Mesorhizobium loti (GENERALIST) APPROACH Lotus japonicus soil microbiota Symbiotic nitrogen fixation binary interaction to Symbiotic nitrogen fixation community interaction
How diverse is the bacterial community associated with Lotus japonicus grown in soil? Cooperative work with Paul Schulze-Lefert nodule root 454 Sequencing of 16S rrna amplicons
Root and rhizosphere bacterial communities are altered in the absence of nitrogen-fixation
Lotus plants grown in Cologne soil Rhizobiales Nodules host a distinct but not restrictive bacterial community
1. Epidermal events leading to rhizobial infection 2. Cortical events controlling nodule infection by rhizobia and the onset of nitrogen fixation Desbrosses, 2011 3. Rhizobial infection consequences for the root-associated microbiota
The plant root microbiome AM symbiosis Philippot et al. 2013, Nature Reviews Microbiology
root nodule soil rhizosphere
The Nod-Factor (LCO)
Symbiosis with rhizobia Flavonoids Rhizobia Nod-Factor
Legume-Rhizobia symbiosis integrated in the complex plant-microbiota interaction
Specificity for nodulation vs. specificity for infection
KAW12 colonised nodules of total nodules - frequency M. loti-gfp + KAW12 DsRed 8% M. loti exou-gfp + KAW12 DsRed 33% M. loti exou-gfp + KAW12 eps PssN-DsRed 0% KAW12 EPS are required for endophytic colonisation of Lotus nodules