The determinant of potyvirus ability to overcome the RTM resistance of Arabidopsis thaliana maps to the N-terminal region of the coat protein

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.

Multiple resistance traits control Plum pox virus infection in Arabidopsis thaliana

Twelve Arabidopsis accessions were challenged with Plum pox potyvirus (PPV) isolates representative of the four PPV strains. Each accession supported local and systemic infection by at least some of the PPV isolates, but high variability was observed in the behavior of the five PPV isolates or the 12 Arabidopsis accessions. Resistance to local infection or long-distance movement occurred in about 40% of all the accession-isolate combinations analyzed. Except for Nd-1, all accessions showed resistance to local infection by PPV-SoC; in the Landsberg erecta (Ler) accession, this resistance was compromised by sgt1 and rar1 mutations, suggesting that it could be controlled by an R gene-mediated resistance pathway. While most of the susceptible accessions were symptomless, PPV induced severe symptoms on inflorescences in C24, Ler, and Bay-0 as early as 15 days after inoculation. Genetic analyses indicated that these interaction phenotypes are controlled by different genetic systems. The restriction of long-distance movement of PPV-El Amar and of another member of genus Potyvirus, Lettuce mosaic virus, in Col-0 requires the RTM genes, indicating for the first time that the RTM system may provide a broad range, potyvirus-specific protection against systemic infection. The restriction to PPV-PS long-distance movement in Cvi-1 is controlled by a single recessive gene, designated rpv1, which was mapped to chromosome 1. The nuclear inclusion polymerase b-capsid protein region of the viral genome appears to be responsible for the ability of PPV-R to overcome rpv1-mediated resistance.