Plant innate immunity is mediated by Resistance (R)
proteins, which bear a striking resemblance to animal molecules of similar function. Tobacco N is a TIR-NB-LRR R gene that confers resistance to Tobacco mosaic virus, specifically the p50 helicase
domain. An intriguing question is how plant R proteins recognize the presence of
pathogen-
derived Avirulence (Avr)
elicitor proteins. We have used biochemical cell fraction and immunoprecipitation in addition to confocal fluorescence microscopy of living tissue to examine the
association between N and p50. Surprisingly, both N and p50 are cytoplasmic and nuclear proteins, and N''s nuclear localization is required for its function. We also demonstrate an in planta association between N and p50. Further, we show that N''s TIR domain is critical for this association, and indeed, it alone can associate with p50. Our results differ from current models for plant innate immunity that propose detection is mediated solely through the LRR domains of these molecules. The data we present support an intricate process of pathogen elicitor recognition by R proteins involving
multiple subcellular compartments and the formation of multiple protein complexes.
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