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

We describe the first system in which a hypersensitive response (HR) i s observed after viral infection of Arabidopsis thaliana. Most ecotype s of Arabidopsis are highly susceptible to turnip crinkle virus (TCV); however, we developed two lines from the ecotype Dijon that exhibit d ramatic differences in TCV susceptibility. Inoculation of the resistan t line, Di-17, resulted in necrotic lesion formation on the inoculated leaves. Virus was restricted to these lesions, and no disease symptom s were observed on the uninoculated portions of most plants. Genes enc oding 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 l eaves, whereas upper, uninoculated leaves accumulated mRNA for these g enes at slightly later times and to lower levels. In contrast, the sus ceptible line, Di-3, did not express a HR. TCV was detected throughout these plants by 3 days post-inoculation. Systemic disease symptoms ap peared a few days later and became increasingly severe until plant dea th. PR gene induction in both inoculated and uninoculated leaves occur red later and to a lesser extent than in Di-17. Several developmental and environmental conditions also were assessed for their effect on th e TCV-resistance levels exhibited by Di-17 and Di-3.