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PLANTS INTERACTING WITH OTHER ORGANISMS

Overlap of Proteome Changes in Medicago truncatula in Response to Auxin and Sinorhizobium meliloti^1,[W],[OA]

Australian Research Council Centre of Excellence for Integrative Legume Research (G.E.v.N., N.G., F.I.P., B.G.R., U.M.), Genomic Interactions Group, Research School of Biological Sciences (G.E.v.N., T.K., N.G., B.G.R.), and School of Biochemistry and Molecular Biology (G.E.v.N., T.K., R.W., F.I.P., U.M.), Australian National University, Canberra, Australian Capital Territory 0200, Australia

We used proteome analysis to identify proteins induced during nodule initiation and in response to auxin in Medicago truncatula. From previous experiments, which found a positive correlation between auxin levels and nodule numbers in the M. truncatula supernodulation mutant sunn (supernumerary nodules), we hypothesized (1) that auxin mediates protein changes during nodulation and (2) that auxin responses might differ between the wild type and the supernodulating sunn mutant during nodule initiation. Increased expression of the auxin response gene GH3:-glucuronidase was found during nodule initiation in M. truncatula, similar to treatment of roots with auxin. We then used difference gel electrophoresis and tandem mass spectrometry to compare proteomes of wild-type and sunn mutant roots after 24 h of treatment with Sinorhizobium meliloti, auxin, or a control. We identified 131 of 270 proteins responding to treatment with S. meliloti and/or auxin, and 39 of 89 proteins differentially displayed between the wild type and sunn. The majority of proteins changed similarly in response to auxin and S. meliloti after 24 h in both genotypes, supporting hypothesis 1. Proteins differentially accumulated between untreated wild-type and sunn roots also showed changes in auxin response, consistent with altered auxin levels in sunn. However, differences between the genotypes after S. meliloti inoculation were largely not due to differential auxin responses. The role of the identified candidate proteins in nodule initiation and the requirement for their induction by auxin could be tested in future functional studies.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ulrike Mathesius (ulrike.mathesius{at}anu.edu.au).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.099978

^* Corresponding author; e-mail ulrike.mathesius{at}anu.edu.au; fax 61–2–6125–0313.

Received March 22, 2007; accepted April 13, 2007; published April 27, 2007.