Plant immune responses are triggered by pattern recognition receptors that detect conserved pathogen-associated molecular patterns (PAMPs) or by resistance (R) proteins recognizing isolate-specific pathogen effectors. We show that in barley, intracellular mildew A (MLA) R proteins function in the nucleus to confer resistance against the powdery mildew fungus. Recognition of the fungal avirulence A10 effector by MLA10 induces nuclear associations between receptor and WRKY transcription factors. The identified WRKY proteins act as repressors of PAMP-triggered basal defense. MLA appears to interfere with the WRKY repressor function, thereby de-repressing PAMP-triggered basal defense. Our findings reveal a mechanism by which these polymorphic immune receptors integrate distinct pathogen signals.

WRKY proteins comprise a large family of transcription factors. Despite their dramatic diversification in plants, WRKY genes seem to have originated in early eukaryotes. The cognate DNA-binding site of WRKY factors is well defined, but determining the roles of individual family members in regulating specific transcriptional programs during development or in response to environmental signals remains daunting. This review summarises the recent advances made in starting to unravel the various functions controlled by WRKY proteins.Addresses

Regulatory proteins play critical roles in controlling the kinetics of various cellular processes during the entire life span of an organism. Leaf senescence, an integral part of the plant developmental program, is Wne-tuned by a complex transcriptional regulatory network ensuring a successful switch to the terminal life phase. To expand our understanding on how transcriptional control coordinates leaf senescence, we characterized AtWRKY70, a gene encoding a WRKY transcription factor that functions as a negative regulator of developmental senescence. To gain insight into the interplay of senescence and plant defense signaling pathways, we employed a collection of mutants, allowing us to speciWcally deWne the role of AtWRKY70 in the salicylic acid-mediated signaling cascades and to further dissect the cross-talk of signal transduction pathways during the onset of senescence in Arabidopsis thaliana. Our results provide strong evidence that AtWRKY70 inXuences plant senescence and defense signaling pathways. These studies could form the basis for further unraveling of these two complex interlinked regulatory networks.