Susceptibility and symptom development in Arabidopsis thaliana to Tobacco mosaic virus is influenced by virus cell-to-cell movement

To identify host factors that regulate susceptibility to Tobacco mosaic vir us (TMV), 14 Arabidopsis thaliana ecotypes were screened for their ability to support TMV systemic movement. The susceptibility phenotypes observed in cluded one ecotype that permitted rapid TMV movement accompanied by symptom s, nine ecotypes that allowed a slower intermediate rate of systemic moveme nt without symptoms, and four ecotypes that allowed little or no systemic T MV movement. Molecular comparisons between ecotypes representing the rapid (Shahdara), intermediate (Col-1), and slow (Tsu-1) movement phenotypes reve aled a positive correlation between the ability of TMV to move cell to cell and its speed of systemic movement. Additionally, protoplasts prepared fro m all three ecotypes supported similar levels of TMV replication, indicatin g that viral replication did not account for differences in systemic moveme nt. Furthermore, induction of the pathogenesis-related genes PR-1 and PR-5 occurred only in the highly susceptible ecotype Shahdara, demonstrating tha t reduced local and systemic movement in Col-1 and Tsu-1 was not due to the activation of known host defense responses. Genetic analysis of F2 progeny derived from crosses made between Shahdara and Tsu-1 or Col-1 and Tsu-1 sh owed the faster cell-to-cell movement phenotypes of Shahdara and Col-1 segr egated as single dominant gems, In addition, the Shahdara symptom phenotype segregated independently as a single recessive gene. Taken together, these findings suggest that, within Arabidopsis ecotypes; at least two genes mod ulate susceptibility to TMV.