Specific Arabidopsis HSP90.2 alleles recapitulate RAR1 cochaperone function in plant NB-LRR disease resistance protein regulation

doi:10.1073/pnas.0904877106

Specific Arabidopsis HSP90.2 alleles recapitulate RAR1 cochaperone function in plant NB-LRR disease resistance protein regulation

Departments of ^aBiology and
^cMicrobiology and Immunology,
^bCurriculum in Genetics and Molecular Biology, and
^dCarolina Center for Genome Sciences, University of North Carolina, Chapel Hill, NC 27599

Contributed by Jeffery L. Dangl, May 3, 2009
↵¹D.A.H. and Y.H. contributed equally to this work. (received for review April 10, 2009)

Abstract

Both plants and animals require the activity of proteins containing nucleotide binding (NB) domain and leucine-rich repeat (LRR) domains for proper immune system function. NB-LRR proteins in plants (NLR proteins in animals) also require conserved regulation via the proteins SGT1 and cytosolic HSP90. RAR1, a protein specifically required for plant innate immunity, interacts with SGT1 and HSP90 to maintain proper NB-LRR protein steady-state levels. Here, we present the identification and characterization of specific mutations in Arabidopsis HSP90.2 that suppress all known phenotypes of rar1. These mutations are unique with respect to the many mutant alleles of HSP90 identified in all systems in that they can bypass the requirement for a cochaperone and result in the recovery of client protein accumulation and function. Additionally, these mutations separate HSP90 ATP hydrolysis from HSP90 function in client protein folding and/or accumulation. By recapitulating the activity of RAR1, these novel hsp90 alleles allow us to propose that RAR1 regulates the physical open–close cycling of a known “lid structure” that is used as a dynamic regulatory HSP90 mechanism. Thus, in rar1, lid cycling is locked into a conformation favoring NB-LRR client degradation, likely via SGT1 and the proteasome.

Footnotes

⁵To whom correspondence should be addressed. E-mail: dangl{at}email.unc.edu
This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected in 2007.
Author contributions: D.A.H., Y.H., P.T., and J.L.D. designed research; D.A.H., Y.H., B.C.M., and P.T. performed research; D.A.H., B.C.M., and P.T. contributed new reagents/analytic tools; D.A.H., Y.H., and J.L.D. analyzed data; and D.A.H., Y.H., and J.L.D. wrote the paper.
↵²Present address: BASF Plant Sciences LLC, Research Triangle Park, NC 27709.
↵³Present address: Athenix Corp., Research Triangle Park, NC 27709.
↵⁴Present address: Instituto de Biología Molecular y Celular de Plantas, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0904877106/DCSupplemental.
Freely available online through the PNAS open access option.