Molecular analysis of resistance mechanisms to Orobanche cumana in sunflower

Authors

  • P. Letousey,

    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
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  • A. De Zélicourt,

    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
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  • C. Vieira Dos Santos,

    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
    2. Dipartimento Scientifico e Tecnologico, Università di Verona, Ca’ Vignal 1, Strada Le Grazie 15, 37134 Verona, Italia; and
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  • S. Thoiron,

    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
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  • F. Monteau,

    1. Laboratoire d’Etude des Résidus et des Contaminants dans les Aliments, Ecole Nationale Vétérinaire, BP 50707, 44307 Nantes Cedex 3, France
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  • P. Simier,

    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
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  • P. Thalouarn,

    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
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  • P. Delavault

    Corresponding author
    1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssinière, BP 92208, Nantes, F-44000 France;
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E-mail: philippe.delavault@univ-nantes.fr

Abstract

Resistance to the dicotyledenous parasite Orobanche cumana in sunflower is characterized by a low number of parasitic attachments and a confinement of the parasite in host tissues leading to its necrosis. To help understand what determines such resistance mechanisms, molecular, biochemical and histological approaches were employed before (early response) and after (late response) attachment of the broomrape parasite to susceptible (2603) and resistant (LR1) sunflower genotypes. The expression patterns of 11 defence-related genes known to be involved in different metabolic pathways (phenylpropanoids, jasmonate, ethylene) and/or in resistance mechanisms against microorganisms were investigated. RT-PCR and cDNA blot experiments revealed that the resistant genotype exhibited a stronger overall defence response against O. cumana than the susceptible one, involving marker genes of the jasmonate (JA) and salicylic acid (SA) pathways. Among them, the SA-responsive gene, def. (defensin), appeared to be characteristic of LR1 sunflower resistance. However, no JA accumulation and similar SA contents (250–300 ng g−1 FW) were measured by GC/MS in both genotypes, parasitized or not. In addition, three cDNAs, isolated by a suppression-subtractive hybridization, were shown to be strongly induced only in the resistant genotype 8 days post-inoculation, when the first O. cumana attachments occurred. These genes, putatively encoding a methionine synthase, a glutathione S-transferase and a quinone oxidoreductase, might be involved in detoxification of reactive oxygen species, suggesting the occurrence of an oxidative burst during the incompatible interaction. Finally, host cell-wall modifications leading to parasite-confinement were correlated with more intense callose depositions in the resistant genotype, concomitant with over-expression of the callose synthase cDNA HaGSL1.

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