RESISTANCE AND SUSCEPTIBLE RESPONSES OF ARABIDOPSIS-THALIANA TO TURNIP CRINKLE VIRUS

We describe the first system in which a hypersensitive response (HR) is observed after viral infection of Arabidopsis thaliana. Most ecotypes of Arabidopsis are highly susceptible to turnip crinkle virus (TCV); however, we developed two lines from the ecotype Dijon that exhibit dramatic differences in TCV susceptibility. Inoculation of the resistant line, Di-17, resulted in necrotic lesion formation on the inoculated leaves. Virus was restricted to these lesions, and no disease symptoms were observed on the uninoculated portions of most plants. Genes encoding the acidic pathogenesis-related (PR) proteins PR-1, PR-2, and PR-5 and the basic form of PR-3 were induced rapidly in the inoculated leaves, whereas upper, uninoculated leaves accumulated mRNA for these genes at slightly later times and to lower levels. In contrast, the susceptible line, Di-3, did not express a HR. TCV was detected throughout these plants by 3 days post-inoculation. Systemic disease symptoms appeared a few days later and became increasingly severe until plant death. PR gene induction in both inoculated and uninoculated leaves occurred later and to a lesser extent than in Di-17. Several developmental and environmental conditions also were assessed for their effect on the TCV-resistance levels exhibited by Di-17 and Di-3.