Identification and characterization of a locus (RTM1) that restricts long‐distance movement of tobacco etch virus in Arabidopsis thaliana

Abstract

SummaryScreens of Arabidopsis thaliana for susceptibility to tobacco etch virus (TEV) revealed that each of 10 ecotypes were able to support genome replication and cell-to-cell movement in inoculated leaves. However, only four ecotypes, including C24 and La-er, supported complete infections in which TEV was able to replicate and move from cell to cell and long distances through the vasculature. The rates of cell-to-cell movement of a reporter-tagged TEV strain (TEV-GUS) in inoculated leaves of C24 and Columbia (Col-3) were similar, and infection foci continued to expand in both ecotypes through 10 days post-inoculation. No visible or microscopic hypersensitive or cell death responses were evident in inoculated leaves of Col-3 plants. Infection of neither C24 nor Col-3 plants with TEV-GUS resulted in induction of PR-1a gene expression, which is normally associated with active defence responses and systemic acquired resistance. The genetic basis for the restriction of longdistance movement of TEV-GUS in Columbia was investigated using C24 ⍥ Col-3 crosses and backcrosses and using La-er ⍥ Col-0 recombinant inbred lines. A dominant locus conditioning the restricted TEV infection phenotype was identified on chromosome 1 between markers ATEAT1 and NCC1 at approximately 14 cM in both genetic analyses. This locus was designated RTM1 (restricted TEV movement 1). It is proposed that RTM1 mediates a restriction of long-distance movement through a mechanism that differs substantially from those conditioned by the dominant resistance genes normally associated with genefor-gene interactions.

Cloning of the Arabidopsis RTM1 gene, which controls restriction of long-distance movement of tobacco etch virus

“…Genomic DNA was isolated from inflorescence tissue as described (11). A bacterial artificial chromosome (BAC) contig between markers ATEAT1 and F17J18-M was assembled from hybridization data generated by the Arabidopsis thaliana Genome Center (http:͞͞genome.bio.…”

“…Rosette leaves were dusted with carborundum and inoculated with TEV-GUS, a recombinant TEV strain encoding GUS (17). GUS activity assays were done by using inflorescence tissue at 15 and 20 days postinoculation (11). Inoculated leaves from plants that scored negative in GUS activity assays of systemic tissue were tested for infection by in situ histochemical assay (17).…”

“…The tobacco etch virus (TEV)-Arabidopsis model system was established to identify host genes that control susceptibility to, and defense against, viruses (11,12). Some ecotypes (e.g., C24 and La-er) are fully susceptible, supporting replication, cell-tocell movement, and long-distance (vasculature-dependent) movement of TEV, whereas other ecotypes (e.g., Col-0 and Ws-2) restrict TEV to inoculated leaves.…”

“…The restriction of TEV involves neither formation of hypersensitive reaction lesions nor activation of systemic acquired resistance. This natural variation in susceptibility is conditioned by the RTM1 locus (11), where the dominant allele confers the restricted infection phenotype. A mutational analysis of Col-0 plants revealed that the restricted infection phenotype is a multigenic trait that requires at least three loci, RTM1, RTM2, and RTM3 (12) (unpublished data).…”

Tobacco mosaic virus: a pioneer to cell–to–cell movement

“…For example, the P30 protein of TMV can bind and, by implication, transport any single-stranded nucleic acid (Citovsky et al 1990(Citovsky et al , 1992a. In contrast, the RCNMV movement protein is capable of tra¤cking ssRNA but not ssDNA or dsDNA (Fujiwara et al 1993), whereas the bean dwarf mosaic begomovirus (BDMV) BL1 movement protein facilitates transport of dsDNA but not ssDNA nor ssRNA molecules (Noueiry et al 1994). However, transport of BDMV dsDNA seems incompatible with biochemical and genetic evidence obtained with another bipartite begomovirus, squash leaf curl virus (SqLCV), for which the transported form is thought to be genomic ssDNA (Pascal et al 1994).…”