The RTM Resistance to Potyviruses in Arabidopsis thaliana: Natural Variation of the RTM Genes and Evidence for the Implication of Additional Genes

Background: The non conventional RTM (Restricted Tobacco etch virus Movement) resistance which restricts long distance movement of some plant viruses in Arabidopsis thaliana is still poorly understood. Though at least three RTM genes have been identified, their precise role(s) in the process as well as whether other genes are involved needs to be elucidated. Methodology/Principal Findings: In this study, the natural variation of the RTM genes was analysed at the amino acid level in relation with their functionality to restrict the long distance movement of Lettuce mosaic potyvirus (LMV). We identified non-functional RTM alleles in LMV-susceptible Arabidopsis accessions as well as some of the mutations leading to the non-functionality of the RTM proteins. Our data also indicate that more than 40% of the resistant accessions to LMV are controlled by the RTM genes. In addition, two new RTM loci were genetically identified. Conclusions/Significance: Our results show that the RTM resistance seems to be a complex biological process which would involves at least five different proteins. The next challenges will be to understand how the different RTM protein domains are involved in the resistance mechanism and to characterise the new RTM genes for a better understanding of the blocking of the long distance transport of plant viruses.