Abdelhafid Bendahmane,1 and
1INRA-URGV and Université Evry Val d'Essonne 2 rue Gaston Crémieux CP 5708 91057 EVRY Cedex, France; 2équipe de Virologie, UMR GDPP, INRA and Université Victor Ségalen Bordeaux 2, IBMV, Campus INRA, BP81, 33883 Villenave d'Ornon Cedex, France
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Accepted 11 April 2008.
Rx-mediated resistance was analyzed in Rx-expressing transgenic Nicotiana plants. The infection outcome of nine Potato virus X isolates mutated at amino acid positions 121 and 127 of the coat protein (CP) confirmed the key role of these amino acids but provided a more complex picture than previously reported. In particular, in Rx-expressing Nicotiana spp., eliciting activity modulated by amino acid 121 was conditioned by the nature of amino acid 127. These results suggest that the specificity of recognition might be modulated by host factors that are somehow subtly modified between Rx-expressing potato and Rx-expressing transgenic Nicotiana plants. Moreover, the CP of three Potexviruses, Narcissus mosaic virus (NMV), White clover mosaic virus (WClMV), and Cymbidium mosaic virus (CymMV), are all recognized by the Rx-based machinery and able to trigger an Rx-dependant hypersensitive response. A smaller elicitor of 90 amino acids was identified in the CP of NMV and WClMV, which contains the previously identified key positions 121 and 127. This elicitor is only weakly conserved (approximately 40% identity) among the CP of the various recognized viruses, suggesting that the Rx molecular machinery targets a conserved structural element of the Potexvirus CP rather than a conserved amino acid motif.
Additional keywords:extreme resistance, hypersensitive response.
© 2008 The American Phytopathological Society