Minisymposium 26: Plant Pathogen Interactions
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M2602: Specific bacterial type III effectors suppress MAMP and MAPK signaling in Arabidopsis nonhost immunity
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Presenter: |
Shan, Libo Contact Presenter | Authors | Shan, Libo (A) He, Ping (A) Lin, Nai-Chun (B) Martin, Gregory B. (B) Kemmerling, Birgit (C) Nurnberger, Thorsten (C) Sheen, Jen (A) | | Affiliations: |
(A): Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02114
(B): Boyce Thompson Institute for Plant Research, and Department of Plant Pathology, Cornell University, Ithaca, NY 14853
(C): Eberhard-Karls-Universitat Tubingen, Zentrum fur Molekularbiologie der Pflanzen (ZMBP), Auf der Morgenstelle 5, D-72076 Tubingen, Germany
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Nonhost immunity is the most prevalent form of plant defense against a broad spectrum of potential pathogens by largely unknown mechanisms. In Arabidopsis, nonhost/nonpathogenic Pseudomonas syringae sustains but pathogenic P. syringae suppresses early and specific MAMP (microbe-associated molecular pattern) marker gene activation. We performed a cell-based genetic screen of virulence type III effectors and identified AvrPto and AvrPtoB as potent and unique suppressors of early defense gene transcription and MAP kinase (MAPK) signaling. AvrPto and AvrPtoB specifically target convergent defense signaling activated by multiple MAMPs upstream of MAPKKK at the plasma membrane linked to the receptor, but do not interfere with the gene-for-gene defense triggered by AvrRpt2, AvrRpm1 and AvrB. 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 uncover the molecular link between nonhost immunity and the conserved MAMP/MAPK signaling in plants, and reveal a novel action of type III effectors from pathogenic bacteria. The distinct AvrPto/AvrPtoB actions in triggering the specialized resistance protein-mediated defense in tomato but blocking MAMP-mediated immunity in Arabidopsis illustrate the fascinating and dynamic coevolution in plant-bacterium battlefield.
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