The Role of a Host Protein (TIP) in the Resistance Response of Arabidopsis to Turnip Crinkle Virus Infection.

Abstract

Our research on Turnip crinkle virus (TCV) has shown that the viral capsid protein (CP) is both a virulence factor as well as the elicitor of a hypersensitive resistance response (HR) to the virus in Arabidopsis. Initially, we identified a protein from Arabidopsis that specifically interacted with the viral CP using a yeast two-hybrid screen. This protein, designated TIP for TCV-Interacting Protein, is a member of the NAC family of plant transcription factors implicated in the regulation of development and senescence. When TCV CP was mutated to eliminate its ability to interact with TIP, the corresponding virus mutants broke the HR-mediated resistance conferred by the HRT resistance (R) gene in Arabidopsis ecotype Dijon (Di)-17. This result suggested that TIP is a component of the signal transduction pathway that leads to the genetically specified TCV resistance. We next confirmed that TIP and the viral CP interact in plant cells and that this interaction prevents nuclear localization of this transcription factor. We demonstrated that TCV CP suppresses post-transcriptional gene silencing (PTGS), a newly discovered RNA-mediated defense system in plants. Together these results suggest that the CP is a virulence factor that could well be functioning through its interaction with TIP. We havemore » proposed a model involving the role of TIP and CP in triggering HR mediated plant defense that fits with the current thinking about how gene-for-gene resistance may function. A unique component of our system is the opportunity to link R-gene function with the newly discovered RNA silencing pathway that is not only a potent defense against viral pathogens, but also regulates early development in plants. In the current funding period we made several significant findings: First, we completed an array analysis comparing gene expression in Arabidopsis infected with TCV and a mutant virus unable to bind TIP. Second, we produced transgenic lines that over-express and inducibly under-express TIP. These accomplishments now form the basis for our continued effort towards providing a complete understanding of molecular events leading to susceptible and resistant interactions between TCV and Arabidopsis plants. Our data strongly suggest that TIP is involved in activating the SA-mediated defense pathway and that TCV CP acts to repress this role of TIP.« less