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Evolutionary Pathways to Break Down the Resistance of Allelic Versions of the PVY Resistance Gene va

November 2014 , Volume 98 , Number  11
Pages  1,521 - 1,529

B. Janzac , INRA-Agrocampus Ouest-Université Rennes 1, UMR 1349 IGEPP, F-35653 Le Rheu, France; Imperial Tobacco Group, SEITA, Institut du Tabac, Domaine de la Tour, F-24100 Bergerac France; and INRA-Cirad Montpellier SupAgro, UMR 385 BGPI, Cirad TA A-54K, Campus International de Baillarguet, F-34398 Montpellier, France ; M. Tribodet , INRA-Agrocampus Ouest-Université Rennes 1 ; C. Lacroix , INRA-Agrocampus Ouest-Université Rennes 1 and Imperial Tobacco Group, SEITA, Institut du Tabac ; B. Moury , INRA, UR407 Pathologie Végétale, Domaine Saint Maurice, BP94, F-84140 Montfavet, France ; J. L. Verrier , Imperial Tobacco Group, SEITA, Institut du Tabac ; and E. Jacquot , INRA-Agrocampus Ouest-Université Rennes 1 and INRA-Cirad Montpellier SupAgro



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Accepted for publication 24 April 2014.
Abstract

Emergence of viral genotypes can make control strategies based on resistance genes ineffective. A few years after the deployment of tobacco genotypes carrying alleles of the Potato virus Y (PVY) recessive resistance gene va, virulent PVY isolates have been reported, suggesting the low durability of va. To have a broader view of the evolutionary processes involved in PVY adaptation to va, we studied mutational pathways leading to the emergence of PVY resistance-breaking populations. The viral genome-linked protein (VPg) has been described to be potentially involved in va adaptation. Analyses of the VPg sequence of PVY isolates sampled from susceptible and resistant tobacco allowed us to identify mutations in the central part of the VPg. Analysis of the virulence of wild-type isolates with known VPg sequences and of mutated versions of PVY infectious clones allowed us to (i) validate VPg as the PVY virulence factor corresponding to va, (ii) highlight the fact that virulence gain in PVY occurs rapidly and preferentially by substitution at position AA105 in the VPg, and (iii) show that the 101G substitution in the VPg of a PVYC isolate is responsible for cross-virulence toward two resistance sources. Moreover, it appears that the evolutionary pathway of PVY adaptation to va depends on both virus and host genetic backgrounds.



Copyright © 2014 The American Phytopathological Society