Prayitno, JokoImin, NijatRolfe, BarryMathesius, Ulrike2015-12-071535-3893http://hdl.handle.net/1885/17698Ethylene 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.Keywords: albumin; albumin 2; ascorbate peroxidase; cyclopropanecarboxylic acid derivative; ethylene; heat shock protein; protein CPRD49; protein pprg 2; proteinase inhibitor; serine proteinase inhibitor; trypsin inhibitor; unclassified drug; vegetable protein; art Ethylene; Medicago truncatula; Model legume; Nodulation; Protein identification; Sickle mutant; Sinorhizobium meliloti200610.1021/pr06026462015-12-07