Molecular Plant Advance Access published online on March 21, 2008
Molecular Plant, doi:10.1093/mp/ssn009
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© The Author 2008. Published by Oxford University Press on behalf of CSPP and IPPE, SIBS, CAS.
Transcomplementation, but not Physical Association of the CC-NB-ARC and LRR Domains of Tomato R Protein Mi-1.2 is Altered by Mutations in the ARC2 Subdomain
a Plant Pathology, Swammerdam Institute for Life Sciences, University of Amsterdam, PO Box 94062, 1090 GB Amsterdam, the Netherlands
b Max Planck Institute for Informatics, Stuhlsatzenhausweg 85, 66123 Saarbrücken, Germany
1 To whom correspondence should be addressed. E-mail takken{at}science.uva.nl, fax +31 205257934, tel. +31 205257795.
Race-specific disease resistance in plants is mediated by Resistance (R) proteins that recognize pathogen attack and initiate defence responses. Most R proteins contain a central NB-ARC domain and a C-terminal leucine-rich repeat (LRR) domain. We analyzed the intramolecular interaction of the LRR domain of tomato R protein Mi-1.2 with its N-terminus. We expressed the CC-NB-ARC and LRR parts in trans and analyzed functional transcomplementation and physical interactions. We show that these domains functionally transcomplement when expressed in trans. Known autoactivating LRR domain swaps were found to induce a hypersensitive response (HR) upon co-expression. Likewise, autoactivating mutants in the NB subdomain transcomplemented to induce HR. Point mutations in the ARC2 subdomain that induce strong autoactivation in the full-length Mi-1.2 protein, however, fail to induce HR in the transcomplementation assay. These data indicate distinct functions for the NB-ARC subdomains in induction of HR signalling. Furthermore, dissociation of the LRR is not required to release its negative regulation, as in all combinations of CC-NB-ARC and LRR domains tested, a physical interaction was observed.