RNA-MEDIATED VIRUS-RESISTANCE IN TRANSGENIC PLANTS - EXPLOITATION OF A CELLULAR PATHWAY POSSIBLY INVOLVED IN RNA DEGRADATION

Transgenic Nicotiana tabacum cv. Burley 49 plants were generated that express the 5' untranslated region of the tobacco etch potyvirus (TEV) genome ligated to a mutated version of the TEV coat protein gene sequ ence that rendered it untranslatable. Eight different transgenic plant lines were analyzed for transgene expression and for resistance to TE V. Three different responses were noted when the transgenic plant line s were inoculated with TEV: 1) some were highly resistant, and no viru s replication occurred; 2) some were susceptible but able to recover f rom systemic TEV infection; and 3) some were susceptible to TEV infect ion. Plant tissue displaying the recovery phenotype was analyzed for v irus replication and transgene expression. Recovered tissue could not be infected with TEV and had steady-state transgene RNA levels which w ere five- to eightfold lower than those of unchallenged transgenic pla nt tissue. Nuclear runoff assays suggested a posttranscriptional reduc tion in specific RNA levels. The highly resistant and recovery phenoty pes associated with TEV challenge inoculation and the reduction of ste ady-state RNA levels in recovered transgenic leaf tissue may be manife stations of a common mechanism.