HRT gene function requires interaction between a NAC protein and viral capsid protein to confer resistance to turnip crinkle virus

An Arabidopsis protein was found to interact specifically with the capsid p rotein (CP) of turnip crinkle virus (TCV) through yeast two-hybrid screenin g. This protein, designated TIP (for TCV-interacting protein), was found to be a member of the recently recognized NAC family of proteins. NAC protein s have been implicated in the regulation of development of plant embryos an d flowers. TIP alone was able to activate expression of reporter genes in y east if fused to a DNA binding domain, suggesting that it may be a transcri ptional activator. The TIP binding region in the TCV CP has been mapped to the N-terminal 25 amino acids. Site-directed mutagenesis within this region revealed that loss of the TIP-CP interaction in the yeast two-hybrid assay correlated with loss of the ability of TCV to induce the hypersensitive re sponse and resistance in the TCV-resistant Arabidopsis ecotype Dijon (Di-0 and its inbred line Di-17). These data suggest that TIP is an essential com ponent in the TCV resistance response pathway.