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The Determinant of Potyvirus Ability to Overcome the RTM Resistance of Arabidopsis thaliana Maps to the N-Terminal Region of the Coat Protein

¹UMR GDPP, INRA Université Bordeaux II, IBVM, Centre INRA de Bordeaux, BP 81, 33883 Villenave d'Ornon Cedex; France; ²Centro Nacional de Biotecnología (CSIC), Campus de la Universidad Autónoma de Madrid, 28049 Madrid, Spain; ³Institute of Virology, Department of Plant Virology, Slovak Academy of Sciences, Dúbravská cesta 9, 84505 Bratislava, Slovakia

In Arabidopsis thaliana Columbia (Col-0) plants, the restriction of Tobacco etch virus (TEV) long-distance movement involves at least three dominant RTM (restricted TEV movement) genes named RTM1, RTM2, and RTM3. Previous work has established that, while the RTM-mediated resistance is also effective against other potyviruses, such as Plum pox virus (PPV) and Lettuce mosaic virus (LMV), some isolates of these viruses are able to overcome the RTM mechanism. In order to identify the viral determinant of this RTM-resistance breaking, the biological properties of recombinants between PPV-R, which systemically infects Col-0, and PPV-PSes, restricted by the RTM resistance, were evaluated. Recombinants that contain the PPV-R coat protein (CP) sequence in an RTM-restricted background are able to systemically infect Col-0. The use of recombinants carrying chimeric CP genes indicated that one or more PPV resistance-breaking determinants map to the 5′ half of the CP gene. In the case of LMV, sequencing of independent RTM-breaking variants recovered after serial passages of the LMV AF199 isolate on Col-0 plants revealed, in each case, amino acid changes in the CP N-terminal region, close to the DAG motif. Taken together, these findings demonstrate that the potyvirus CP N-terminal region determines the outcome of the interaction with the RTM-mediated resistance.