TRANSPOSON TAGGING OF TOBACCO MOSAIC-VIRUS RESISTANCE GENE-N - ITS POSSIBLE ROLE IN THE TMV-N-MEDIATED SIGNAL-TRANSDUCTION PATHWAY

Plants can recognize and resist invading pathogens by signaling the in duction of rapid defense responses, Often these responses are mediated by single dominant resistance genes (R genes), The products of R gene s have been postulated to recognize the pathogen and trigger rapid hos t defense responses. Here we describe isolation of the classical resis tance gene N of tobacco that mediates resistance to the well-character ized pathogen tobacco mosaic virus (TMV). The N gene was isolated by t ransposon tagging using the maize Activator (Ac) transposon. We confir med isolation of the N gene by complementation of the TMV-sensitive ph enotype with a genomic DNA fragment. Sequence analysis of the N gene s hows that it encodes a protein,vith an amino-terminal domain similar t o that of the cytoplasmic domains of the Drosophila Toll protein and t be interleukin 1 receptor in mammals, a putative nucleotide-binding si te and 14 imperfect leucine-rich repeats. The presence of these functi onal domains in the predicted N gene product is consistent with the hy pothesis that the N resistance gene functions in a signal transduction pathway. Similarities of N to-Toll and the interleukin 1 receptor sug gest a similar signaling mechanism leading to rapid gene induction and TMV resistance.