THE ARABIDOPSIS NIM1 PROTEIN SHOWS HOMOLOGY TO THE MAMMALIAN TRANSCRIPTION FACTOR INHIBITOR I-KAPPA-B

The NIM1 (for noninducible immunity) gene product is involved in the s ignal transduction cascade leading to both systemic acquired resistanc e (SAR) and gene-for-gene disease resistance in Arabidopsis. We have i solated and characterized five new alleles of nim1 that show a range o f phenotypes from weakly impaired in chemically induced pathogenesis-r elated protein-1 gene expression and fungal resistance to very strongl y blocked. We have isolated the NIM1 gene by using a map-based cloning procedure. Interestingly, the NIM1 protein shows sequence homology to the mammalian signal transduction factor I kappa B subclass alpha. NF -kappa B/I kappa B signaling pathways are implicated in disease resist ance responses in a range of organisms from Drosophila to mammals, sug gesting that the SAR signaling pathway in plants is representative of an ancient and ubiquitous defense mechanism in higher organisms.