title: Mutations inRice yellow mottle virusPolyprotein P2a Involved inRYMV2Gene Resistance Breakdown.
abstract: Rice yellow mottle virus(RYMV) is one of the major diseases of rice in Africa. The high resistance of theOryza glaberrimaTog7291 accession involves a null allele of theRYMV2gene, whose ortholog inArabidopsis,CPR5, is a transmembrane nucleoporin involved in effector-triggered immunity. To optimize field deployment of theRYMV2gene and improve its durability, which is often a weak point in varietal resistance, we analyzed its efficiency toward RYMV isolates representing the genetic diversity of the virus and the molecular basis of resistance breakdown. Tog7291 resistance efficiency was highly variable depending on the isolate used, with infection rates ranging from 0 to 98% of plants. Back-inoculation experiments indicated that infection cases were not due to an incomplete resistance phenotype but to the emergence of resistance-breaking (RB) variants. Interestingly, the capacity of the virus to overcome Tog7291 resistance is associated with a polymorphism at amino-acid 49 of the VPg protein which also affects capacity to overcome the previously studiedRYMV1resistance gene. This polymorphism appeared to be a main determinant of the emergence of RB variants. It acts independently of the resistance gene and rather reflects inter-species adaptation with potential consequences for the durability of resistance. RB mutations were identified by full-length or partial sequencing of the RYMV genome in infected Tog7291 plants and were validated by directed mutagenesis of an infectious viral clone. We found that Tog7291 resistance breakdown involved mutations in the putative membrane anchor domain of the polyprotein P2a. Although the precise effect of these mutations on rice/RYMV interaction is still unknown, our results offer a new perspective for the understanding ofRYMV2mediated resistance mechanisms. Interestingly, in the susceptible IR64 variety, RB variants showed low infectivity and frequent reversion to the wild-type genotype, suggesting that Tog7291 resistance breakdown is associated with a major loss of viral fitness in normally susceptibleO. sativavarieties. Despite the high frequency of resistance breakdown in controlled conditions, this loss of fitness is an encouraging element with regards toRYMV2resistance durability.
authors.affiliation: Interactions Plantes Microorganismes Environnement, Institut de Recherche pour le Développement - Centre de Coopération Internationale en Recherche Agronomique pour le Développement - Université de Montpellier Montpellier, France.
authors.forename: Agnès
authors.initials: A
authors.lastname: Pinel-Galzi
authors.affiliation: Plant Diversity Adaptation and Development Research Unit, Institut de Recherche pour le Développement - Université de Montpellier Montpellier, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Dubreuil-Tranchant
authors.affiliation: Interactions Plantes Microorganismes Environnement, Institut de Recherche pour le Développement - Centre de Coopération Internationale en Recherche Agronomique pour le Développement - Université de Montpellier Montpellier, France.
authors.forename: Eugénie
authors.initials: E
authors.lastname: Hébrard
authors.affiliation: Plant Diversity Adaptation and Development Research Unit, Institut de Recherche pour le Développement - Université de Montpellier Montpellier, France.
authors.forename: Cédric
authors.initials: C
authors.lastname: Mariac
authors.affiliation: Plant Diversity Adaptation and Development Research Unit, Institut de Recherche pour le Développement - Université de Montpellier Montpellier, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Ghesquière
authors.affiliation: Plant Diversity Adaptation and Development Research Unit, Institut de Recherche pour le Développement - Université de Montpellier Montpellier, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Albar
keywords: CPR5; RYMV; deep sequencing; resistance breakdown; rice; virus adaptation