title: Identification of ethylene-mediated protein changes during nodulation in Medicago truncatula using proteome analysis.
abstract: Ethylene has been hypothesised to be a regulator of root nodule development in legumes, but its molecular mechanisms of action remain unclear. The skl mutant is an ethylene-insensitive legume mutant showing a hypernodulation phenotype when inoculated with its symbiont Sinorhizobium meliloti. We used the skl mutant to study the ethylene-mediated protein changes during nodule development in Medicago truncatula. We compared the root proteome of the skl mutant to its wild-type in response to the ethylene precursor aminocyclopropane carboxylic acid (ACC) to study ethylene-mediated protein expression in root tissues. We then compared the proteome of skl roots to its wild-type after Sinorhizobium inoculation to identify differentially displayed proteins during nodule development at 1 and 3 days post inoculation (dpi). Six proteins (pprg-2, Kunitz proteinase inhibitor, and ACC oxidase isoforms) were down-regulated in skl roots, while three protein spots were up-regulated (trypsin inhibitor, albumin 2, and CPRD49). ACC induced stress-related proteins in wild-type roots, such as pprg-2, ACC oxidase, proteinase inhibitor, ascorbate peroxidase, and heat-shock proteins. However, the expression of stress-related proteins such as pprg-2, Kunitz proteinase inhibitor, and ACC oxidase, was down-regulated in inoculated skl roots. We hypothesize that during early nodule development, the plant induces ethylene-mediated stress responses to limit nodule numbers. When a mutant defective in ethylene signaling, such as skl, is inoculated with rhizobia, the plant stress response is reduced, resulting in increased nodule numbers.
authors.affiliation: ARC Centre of Excellence for Integrative Legume Research, Genomic Interactions Group, Research School of Biological Sciences, The Australian National University, Canberra ACT 0200, Australia.
authors.forename: Joko
authors.initials: J
authors.lastname: Prayitno
authors.forename: Nijat
authors.initials: N
authors.lastname: Imin
authors.forename: Barry G
authors.initials: BG
authors.lastname: Rolfe
authors.forename: Ulrike
authors.initials: U
authors.lastname: Mathesius
mesh_terms: D000595:Amino Acid Sequence; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods; D005030:Ethylenes / Q000494:pharmacology*; D046913:Medicago truncatula / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000737:chemistry / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D040901:Proteomics / Q000379:methods*; D016962:Sinorhizobium meliloti
chemical_list: D005030:Ethylenes; D010446:Peptide Fragments; D010937:Plant Growth Regulators; D010940:Plant Proteins; C036216:ethylene