title: MALDI mass spectrometry-assisted molecular imaging of metabolites during nitrogen fixation in the Medicago truncatula-Sinorhizobium meliloti symbiosis.
abstract: Symbiotic associations between leguminous plants and nitrogen-fixing rhizobia culminate in the formation of specialized organs called root nodules, in which the rhizobia fix atmospheric nitrogen and transfer it to the plant. Efficient biological nitrogen fixation depends on metabolites produced by and exchanged between both partners. The Medicago truncatula-Sinorhizobium meliloti association is an excellent model for dissecting this nitrogen-fixing symbiosis because of the availability of genetic information for both symbiotic partners. Here, we employed a powerful imaging technique - matrix-assisted laser desorption/ionization (MALDI)/mass spectrometric imaging (MSI) - to study metabolite distribution in roots and root nodules of M. truncatula during nitrogen fixation. The combination of an efficient, novel MALDI matrix [1,8-bis(dimethyl-amino) naphthalene, DMAN] with a conventional matrix 2,5-dihydroxybenzoic acid (DHB) allowed detection of a large array of organic acids, amino acids, sugars, lipids, flavonoids and their conjugates with improved coverage. Ion density maps of representative metabolites are presented and correlated with the nitrogen fixation process. We demonstrate differences in metabolite distribution between roots and nodules, and also between fixing and non-fixing nodules produced by plant and bacterial mutants. Our study highlights the benefits of using MSI for detecting differences in metabolite distributions in plant biology.
authors.affiliation: School of Pharmacy, University of Wisconsin - Madison, Madison, WI, 53705, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Ye
authors.affiliation: Department of Chemistry, University of Wisconsin - Madison, Madison, WI, 53706, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Gemperline
authors.affiliation: Department of Agronomy, University of Wisconsin - Madison, Madison, WI, 53706, USA.
authors.forename: Muthusubramanian
authors.initials: M
authors.lastname: Venkateshwaran
authors.affiliation: Research Center of Basic Medical Sciences, Tianjin Medical University, Tianjin, 300070, China.
authors.forename: Ruibing
authors.initials: R
authors.lastname: Chen
authors.affiliation: Department of Agronomy, University of Wisconsin - Madison, Madison, WI, 53706, USA.
authors.forename: Pierre-Marc
authors.initials: PM
authors.lastname: Delaux
authors.affiliation: Department of Agronomy, University of Wisconsin - Madison, Madison, WI, 53706, USA.
authors.forename: Maegen
authors.initials: M
authors.lastname: Howes-Podoll
authors.affiliation: Department of Agronomy, University of Wisconsin - Madison, Madison, WI, 53706, USA.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Ané
authors.affiliation: School of Pharmacy, University of Wisconsin - Madison, Madison, WI, 53705, USA.|Department of Chemistry, University of Wisconsin - Madison, Madison, WI, 53706, USA.
authors.forename: Lingjun
authors.initials: L
authors.lastname: Li
mesh_terms: D018506:Gene Expression Regulation, Plant; D005841:Gentisates / Q000737:chemistry; D046913:Medicago truncatula / Q000378:metabolism* / Q000382:microbiology; D055442:Metabolome; D057054:Molecular Imaging / Q000379:methods*; D009284:Naphthols / Q000737:chemistry; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D010641:Phenotype; D055170:Plant Root Nodulation; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D053204:Root Nodules, Plant; D016962:Sinorhizobium meliloti / Q000502:physiology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013559:Symbiosis
chemical_list: D005841:Gentisates; D009284:Naphthols; C038630:1-(N-dimethyl)amino-7-naphthol; D009584:Nitrogen; C010925:2,5-dihydroxybenzoic acid