Dissecting plant defence signal transduction: modifiers ofsnc1inArabidopsis†

Plants have evolved sophisticated defence mechanisms against pathogen infection, during which Resistance (R) proteins play a central role in recognizing pathogens and initiating downstream defence cascades. In Arabidopsis, the dominant mutant snc1 was previously identified that constitutively expresses P athogenesis- R elated(PR) genes and displays enhanced resistance against both bacterial and oomycete pathogens. A point mutation in this gene renders the encoded TIR-NB-LRR type R protein constitutively active without interaction with pathogens. Both suppressor screen and activation tagging approaches were used to identify regulators downstream of snc1. From these efforts, 15 complementation groups of m odifier o f s nc1 (mos) mutants were identified. We have cloned 11 of the mutations using map-based approaches, and have fully characterized mos2 through mos8. Analysis of the corresponding MOS genes and their protein products reveals a complicated signalling network downstream of R protein activation that involves nucleo-cytoplasmic trafficking, transcriptional reprogramming, RNA processing and protein modification.