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The RAP1 Gene Confers Effective, Race-Specific Resistance to the Pea Aphid in Medicago truncatula Independent of the Hypersensitive Reaction

December 2009 , Volume 22 , Number  12
Pages  1,645 - 1,655

Sophie Alice Stewart,1 Simon Hodge,1 Nurul Ismail,1 John W. Mansfield,1 Bart J. Feys,1 Jean-Marie Prospéri,2 Thierry Huguet,3 Cécile Ben,3 Laurent Gentzbittel,3 and Glen Powell1

1Division of Biology, Imperial College London, South Kensington Campus, London. SW7 2AZ, U.K.; 2INRA, UMR DIAPC 1097, Montpellier, F34130 Mauguio, France; 3INP-ENSAT, Symbiose et Pathologie des Plantes--SP2, Pôle de Biotechnologie Végétale, Chemin Borde Rouge, 31326, Castanet Tolosan Cedex, France

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Accepted 3 August 2009.

Plant resistance to pathogens is commonly associated with a hypersensitive response (HR), but the degree to which the HR is responsible for incompatibility is subject to debate. Resistance to aphids is likely to share features with resistance to pathogens but is less well understood. Here, we report effective resistance to the pea aphid Acyrthosiphon pisum in Medicago truncatula. Aphids lost weight and died rapidly (within two days) on the resistant genotype Jemalong, which developed necrotic lesions following infestation. Lesions were induced by nonvascular intracellular stylet punctures by aphids, remained localized to the site of stylet entry, stained for the presence of reactive oxygen species, and were similar to the HR induced by the bacterial pathogen Pseudomonas syringae pv. phaseolicola. The implication that aphid-induced lesions confer resistance was tested by quantitative trait loci analysis using recombinant inbred lines derived from a cross between Jemalong and the susceptible genotype DZA315.16. One major locus, RAP1, was identified that was sufficient to confer race-specific resistance against the pea aphid and was mapped to the middle of chromosome 3. Surprisingly, a separate locus, mapping to the top of chromosome 3, governed aphid-induced HR, indicating that the HR-like lesions are not required for RAP1-mediated aphid resistance.

© 2009 The American Phytopathological Society