Negative regulation of defence signalling pathways by the EDR1 protein kinase

SUMMARY The enhanced disease resistance 1 (edr1) mutant of Arabidopsis confers enhanced resistance to bacterial and fungal pathogens. To better understand how edr1-mediated resistance occurs, we performed transcriptome analyses on wild-type and edr1 plants inoculated with the fungal pathogen Golovinomyces cichoracearum (powdery mildew). The expression of many known and putative defence-associated genes was more rapidly induced, and to higher levels, in edr1 plants relative to the wild-type. Many of the genes with elevated expression encoded WRKY transcription factors and there was enrichment for their binding sites in promoters of the genes upregulated in edr1. Confocal microscopy of transiently expressed EDR1 protein showed that a significant fraction of EDR1 was localized to the nucleus, suggesting that EDR1 could potentially interact with transcription factors in the nucleus. Analysis of gene ontology annotations revealed that genes associated with the endomembrane system, defence, reactive oxygen species (ROS) production and protein kinases were induced early in the edr1 mutant, and that elevated expression of the endomembrane system, defence and ROS-related genes was maintained for at least 4 days after infection.