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Nature. 2015 May 14;521(7551):213-6. doi: 10.1038/nature14243. Epub 2015 Mar 2.

Pathogen-secreted proteases activate a novel plant immune pathway.

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1] Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA [2] Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.


Mitogen-activated protein kinase (MAPK) cascades play central roles in innate immune signalling networks in plants and animals. In plants, however, the molecular mechanisms of how signal perception is transduced to MAPK activation remain elusive. Here we report that pathogen-secreted proteases activate a previously unknown signalling pathway in Arabidopsis thaliana involving the Gα, Gβ, and Gγ subunits of heterotrimeric G-protein complexes, which function upstream of an MAPK cascade. In this pathway, receptor for activated C kinase 1 (RACK1) functions as a novel scaffold that binds to the Gβ subunit as well as to all three tiers of the MAPK cascade, thereby linking upstream G-protein signalling to downstream activation of an MAPK cascade. The protease-G-protein-RACK1-MAPK cascade modules identified in these studies are distinct from previously described plant immune signalling pathways such as that elicited by bacterial flagellin, in which G proteins function downstream of or in parallel to an MAPK cascade without the involvement of the RACK1 scaffolding protein. The discovery of the new protease-mediated immune signalling pathway described here was facilitated by the use of the broad host range, opportunistic bacterial pathogen Pseudomonas aeruginosa. The ability of P. aeruginosa to infect both plants and animals makes it an excellent model to identify novel immunoregulatory strategies that account for its niche adaptation to diverse host tissues and immune systems.

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