IMMUTANS positively regulates RPW8.1-mediated disease resistance in Arabidopsis

Arabidopsis RESISTANCE TO POWDERY MILDEW 8.1(RPW8.1) confers broad-spectrum resistance to both fungal and bacterial pathogens. To uncover the regulatory mechanism of RPW8.1-mediated resistance, we constructed an EMS mutagenesis library based on the Arabidopsis transgenic line R1Y4 expressing RPW8.1-YFP from native promoter. Here, we described a variegation mutant B26m1-4 from the library. Map-based cloning identified a G-to-A point mutation at the border between the 7th intron and the 8th exon of IMMUTANS (IM, AT4G22260) locus, leading to deletion of the entire 8th exon. Although the variegation phenotype is independent of RPW8.1, mutation in IM significantly compromised RPW8.1-mediated resistance against powdery mildew and bacterial pathogens, which were associated with attenuated defense responses, such as H2O2 accumulation, cell death, and callose deposition. Taken together, these data indicate that IM positively regulates RPW8.1-mediated disease resistance.