title: Specific bacterial suppressors of MAMP signaling upstream of MAPKKK in Arabidopsis innate immunity.
abstract: Plants and animals possess innate immune systems to prevent infections and are effectively "nonhosts" for most potential pathogens. The molecular mechanisms underlying nonhost immunity in plants remain obscure. In Arabidopsis, nonhost/nonpathogenic Pseudomonas syringae sustains but pathogenic P. syringae suppresses early MAMP (microbe-associated molecular pattern) marker-gene activation. We performed a cell-based genetic screen of virulence factors and identified AvrPto and AvrPtoB as potent and unique suppressors of early-defense gene transcription and MAP kinase (MAPK) signaling. Unlike effectors of mammalian pathogens, AvrPto and AvrPtoB intercept multiple MAMP-mediated signaling upstream of MAPKKK at the plasma membrane linked to the receptor. In transgenic Arabidopsis, AvrPto blocks early MAMP signaling and enables nonhost P. syringae growth. Deletions of avrPto and avrPtoB from pathogenic P. syringae reduce its virulence. The studies reveal a fundamental role of MAMP signaling in nonhost immunity, and a novel action of type III effectors from pathogenic bacteria.
authors: Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02114, USA.
authors: Ping
authors: P
authors: He
authors: Libo
authors: L
authors: Shan
authors: Nai-Chun
authors: NC
authors: Lin
authors: Gregory B
authors: GB
authors: Martin
authors: Birgit
authors: B
authors: Kemmerling
authors: Thorsten
authors: T
authors: Nürnberger
authors: Jen
authors: J
authors: Sheen