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JXB Advance Access published online on April 4, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern045
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Structure–function analysis of the NB-ARC domain of plant disease resistance proteins

Gerben van Ooijen1 *, Gabriele Mayr2 *, Mobien M. A. Kasiem1, Mario Albrecht2, Ben J. C. Cornelissen1 and Frank L. W. Takken1,{dagger}

1Plant Pathology, Swammerdam Institute for Life Sciences, University of Amsterdam, PO Box 94062, 1090 GB Amsterdam, The Netherlands
2Max Planck Institute for Informatics, Stuhlsatzenhausweg 85, D-66123 Saarbrücken, Germany

{dagger} To whom correspondence should be addressed. E-mail: takken{at}science.uva.nl

Resistance (R) proteins in plants are involved in pathogen recognition and subsequent activation of innate immune responses. Most resistance proteins contain a central nucleotide-binding domain. This so-called NB-ARC domain consists of three subdomains: NB, ARC1, and ARC2. The NB-ARC domain is a functional ATPase domain, and its nucleotide-binding state is proposed to regulate activity of the R protein. A highly conserved methionine–histidine–aspartate (MHD) motif is present at the carboxy-terminus of ARC2. An extensive mutational analysis of the MHD motif in the R proteins I-2 and Mi-1 is reported. Several novel autoactivating mutations of the MHD invariant histidine and conserved aspartate were identified. The combination of MHD mutants with autoactivating hydrolysis mutants in the NB subdomain showed that the autoactivation phenotypes are not additive. This finding indicates an important regulatory role for the MHD motif in the control of R protein activity. To explain these observations, a three-dimensional model of the NB-ARC domain of I-2 was built, based on the APAF-1 template structure. The model was used to identify residues important for I-2 function. Substitution of the selected residues resulted in the expected distinct phenotypes. Based on the model, it is proposed that the MHD motif fulfils the same function as the sensor II motif found in AAA+ proteins (ATPases associated with diverse cellular activities)—co-ordination of the nucleotide and control of subdomain interactions. The presented 3D model provides a framework for the formulation of hypotheses on how mutations in the NB-ARC exert their effects.

Key words: Intramolecular interactions, MHD motif, NB-ARC domain, plant disease resistance, protein structure, R proteins, signal transduction, site-directed mutagenesis

* These authors contributed equally to this work.

Received 17 December 2007; Revised 23 January 2008 Accepted 28 January 2008


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