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Summary: Arabidopsis RESISTANCE TO POWDERY MILDEW 8.2 (RPW8.2) is specifically induced by the powdery mildew (PM) fungus (Golovinomyces cichoracearum) in the infected epidermal cells to activate immunity. However, the mechanism of RPW8.2‐induction is not well understood.Here, we identify a G. cichoracearum effector that interacts with RPW8.2, named Gc‐RPW8.2 interacting protein 1 (GcR8IP1), by a yeast two‐hybrid screen of an Arabidopsis cDNA library.GcR8IP1 is physically associated with RPW8.2 with its REALLY INTERESTING NEW GENE finger domain that is essential and sufficient for the association. GcR8IP1 was secreted and translocated into the nucleus of host cell infected with PM. Association of GcR8IP1 with RPW8.2 led to an increase in RPW8.2 in the nucleus. In turn, the nucleus‐localized RPW8.2 promoted the activity of the RPW8.2 promoter, resulting in transcriptional self‐amplification of RPW8.2 to boost immunity at infection sites. Additionally, ectopic expression or host‐induced gene silencing of GcR8IP1 supported its role as a virulence factor in PM.Altogether, our results reveal a mechanism of RPW8.2‐dependent defense strengthening via altered partitioning of RPW8.2 and transcriptional self‐amplification triggered by a PM fungal effector, which exemplifies an atypical form of effector‐triggered immunity. [ABSTRACT FROM AUTHOR]

To gain insight into the coordination of gene expression profiles under abscisic acid (ABA) and H2O2 applications, global changes in gene expression in response to ABA and H2O2 in Arabidopsis seedlings were investigated using GeneChip (Santa Clara, CA, USA) arrays. Among over 24 000 genes present in the arrays, 459 transcripts were found to be significantly increased, whereas another 221 decreased following H2O2 treatment compared with control. Similar to treatment with H2O2, ABA treatment elevated the transcription of 391 genes and repressed that of 322 genes. One hundred and forty-three upregulated genes and 75 downregulated genes were shared between the two treatments and these genes were mainly involved in metabolism, signal transduction, transcription, defense, and resistance. Only two genes, which encode an APETALA2/dehydration-responsive element binding protein (AP2/DREBP) family transcriptional factor and a late embryogenesis-abundant protein, were downregulated by H2O2, but upregulated by ABA. These results suggest that, similar to ABA, H2O2 plays a global role in gene transcription of Arabidopsis seedlings. The transcriptional responses induced by the application of exogenous ABA and H2O2 overlapped substantially. These two treatments regulated most of the downstream genes in a coordinated manner. (Managing editor: Li-Hui Zhao) [ABSTRACT FROM AUTHOR]