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Partial Resistance of Medicago truncatula to Aphanomyces euteiches Is Associated with Protection of the Root Stele and Is Controlled by a Major QTL Rich in Proteasome-Related Genes

September 2009 , Volume 22 , Number  9
Pages  1,043 - 1,055

Naceur Djébali,1,2,6 Alain Jauneau,3 Carine Ameline-Torregrosa,4 Fabien Chardon,4 Valérie Jaulneau,1,2 Catherine Mathé,1,2 Arnaud Bottin,1,2 Marc Cazaux,1,2 Marie-Laure Pilet-Nayel,5 Alain Baranger,5 Mohamed Elarbi Aouani,6 Marie-Thérèse Esquerré-Tugayé,1,2 Bernard Dumas,1,2 Thierry Huguet,3 and Christophe Jacquet1,2

1Université de Toulouse, UPS, Surfaces Cellulaires et Signalisation chez les Végétaux, BP42617, Auzeville, F-31326, Castanet-Tolosan, France; 2CNRS, Surfaces Cellulaires et Signalisation chez les Végétaux, BP42617, Auzeville, F-31326, Castanet-Tolosan, France; 3IFR40 CNRS. Pôle de Biotechnologie Végétale. BP42617. 31326 Castanet-Tolosan, France; 4Laboratoire Symbiose et Pathologie des Plantes (SP2) -- ENSAT. Pôle de Biotechnologie Végétale, BP32607, 31326 Castanet-Tolosan cedex, France; 5INRA-UMR Amélioration des Plantes et Biotechnologies Végétales. Domaine de la Motte, BP 35327 - 35653 Le Rheu Cedex, France; 6Laboratoire Interactions Légumineuses Microorganismes, Centre de Biotechnologie à la Technopole de Borj Cedria, BP 901, 2050 Hammam-Lif, Tunisia

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Accepted 4 May 2009.

A pathosystem between Aphanomyces euteiches, the causal agent of pea root rot disease, and the model legume Medicago truncatula was developed to gain insights into mechanisms involved in resistance to this oomycete. The F83005.5 French accession and the A17-Jemalong reference line, susceptible and partially resistant, respectively, to A. euteiches, were selected for further cytological and genetic analyses. Microscopy analyses of thin root sections revealed that a major difference between the two inoculated lines occurred in the root stele, which remained pathogen free in A17. Striking features were observed in A17 roots only, including i) frequent pericycle cell divisions, ii) lignin deposition around the pericycle, and iii) accumulation of soluble phenolic compounds. Genetic analysis of resistance was performed on an F7 population of 139 recombinant inbred lines and identified a major quantitative trait locus (QTL) near the top of chromosome 3. A second study, with near-isogenic line responses to A. euteiches confirmed the role of this QTL in expression of resistance. Fine-mapping allowed the identification of a 135-kb sequenced genomic DNA region rich in proteasome-related genes. Most of these genes were shown to be induced only in inoculated A17. Novel mechanisms possibly involved in the observed partial resistance are proposed.

© 2009 The American Phytopathological Society