HYPERSENSITIVE RESPONSE IN CUCUMBER MOSAIC VIRUS-INOCULATED ARABIDOPSIS-THALIANA

The responses of 12 Arabidopsis ecotypes to cucumber mosaic virus strain Y (CMV(Y)) or strain O (CMV(O)) were characterized. Except for ecotype C24, all ecotypes were susceptible to both strains of CMV. In C24, CMV(O) multiplied systemically, but CMV(Y) did not spread systemically and induced only local necrotic spots in virus-inoculated leaves 21-27 h after inoculation. In CMV(Y)-inoculated C24 leaves, virus was confined to the inoculated leaves, and the amount of the pathogenesis-related-1 protein increased during the progress of local necrotic spot formation. These results indicate that C24 mounts a hypersensitive response (HR) to CMV(Y). By genetic analysis of crosses between C24 and ecotype Columbia or Landsberg (erecta) which are susceptible to CMV(Y) infection, the HR to CMV(Y) in C24 was found to be determined by a single major dominant gene whose function was influenced by a modifier gene from the Landsberg ecotype. Comparison of the responses between C24 leaves inoculated with pseudorecombinants of both strains of CMV suggested that the HR was controlled by CMV RNAS. The molecular interaction between the single major gene and CMV(Y) RNA3 is likely to induce the HR in CMV(Y)-inoculated C24.