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The MtMMPL1 Early Nodulin Is a Novel Member of the Matrix Metalloendoproteinase Family with a Role in Medicago truncatula Infection by Sinorhizobium meliloti^1,[W],[OA]

Laboratoire des Interactions Plantes Micro-organismes, Centre National de la Recherche Scientifique-Institut National de la Recherche Agronomique, 31326 Castanet Tolosan cedex, France

We show here that MtMMPL1, a Medicago truncatula nodulin gene previously identified by transcriptomics, represents a novel and specific marker for root and nodule infection by Sinorhizobium meliloti. This was established by determining the spatial pattern of MtMMPL1 expression and evaluating gene activation in the context of various plant and bacterial symbiotic mutant interactions. The MtMMPL1 protein is the first nodulin shown to belong to the large matrix metalloendoproteinase (MMP) family. While plant MMPs are poorly documented, they are well characterized in animals as playing a key role in a number of normal and pathological processes involving the remodeling of the extracellular matrix. MtMMPL1 represents a novel MMP variant, with a substitution of a key amino acid residue within the predicted active site, found exclusively in expressed sequence tags corresponding to legume MMP homologs. An RNA interference approach revealed that decreasing MtMMPL1 expression leads to an accumulation of rhizobia within infection threads, whose diameter is often significantly enlarged. Conversely, MtMMPL1 ectopic overexpression under the control of a constitutive (35S) promoter led to numerous abortive infections and an overall decrease in the number of nodules. We discuss possible roles of MtMMPL1 during Rhizobium infection.

² These authors contributed equally to the article.

³ Present address: PROTENIA SAAl, Akhawayn University International, 53000 Ifrane, Morocco.

⁴ Present address: GEVES-SNES, Rue Georges Morel, BP 24, 49071 Beaucouze, France.

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: Pascal Gamas (pascal.gamas{at}toulouse.inra.fr).

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

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.092585

^* Corresponding author; e-mail pascal.gamas{at}toulouse.inra.fr; fax 33–561–28–50–61.

Received November 6, 2006; accepted January 20, 2007; published February 9, 2007.

This article has been cited by other articles:

				J. P. Combier, F. de Billy, P. Gamas, A. Niebel, and S. Rivas Trans-regulation of the expression of the transcription factor MtHAP2-1 by a uORF controls root nodule development Genes & Dev., June 1, 2008; 22(11): 1549 - 1559. [Abstract] [Full Text] [PDF]

				K. M. Jones, N. Sharopova, D. P. Lohar, J. Q. Zhang, K. A. VandenBosch, and G. C. Walker Differential response of the plant Medicago truncatula to its symbiont Sinorhizobium meliloti or an exopolysaccharide-deficient mutant PNAS, January 15, 2008; 105(2): 704 - 709. [Abstract] [Full Text] [PDF]