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JXB Advance Access originally published online on September 5, 2005
Journal of Experimental Botany 2005 56(420):2683-2693; doi:10.1093/jxb/eri261
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© The Author [2005]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved.

RESEARCH PAPER

Resistance of sunflower to the biotrophic oomycete Plasmopara halstedii is associated with a delayed hypersensitive response within the hypocotyls

O. Radwan, S. Mouzeyar, J. S. Venisse, P. Nicolas and M. F. Bouzidi*

UMR 1095 INRA-UBP ‘Amélioration et Santé des Plantes’, Université Blaise Pascal, 24 avenue des Landais, F-63177 Aubière Cedex, France

* To whom correspondence should be addressed. Fax: +33 4 73407914. E-mail: m-fouad.bouzidi{at}univ-bpclermont.fr

The biotrophic oomycete Plasmopara halstedii is the causal agent of downy mildew in sunflower. It penetrates the roots of both susceptible and resistant sunflower lines and grows through the hypocotyls towards the upper part of the seedling. RT-PCR analysis has shown that resistance is associated with the activation of a hsr203J-like gene, which is a molecular marker of the hypersensitive reaction in tobacco. Activation of this gene was specifically observed during the incompatible interaction and coincided with cell collapse in the hypocotyls. This HR was also associated with the early and local activation of the NPR1 gene which is a key component in the establishment of the SAR. No such HR or a significant activation of the hsr203J-like gene were observed during the compatible combination. These results suggest that the resistance of sunflower to P. halstedii is associated with an HR which fails to halt the parasite. By contrast, this HR triggers a SAR which takes places in the upper part of the hypocotyls and eventually leads to the arrest of parasite growth. A model describing the resistance of plants to root-infecting oomycetes is proposed.

Key words: Defence related genes, Helianthus annuus, hypersensitive reaction, Plasmopara halstedii


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