title: The small heat shock protein 20 RSI2 interacts with and is required for stability and function of tomato resistance protein I-2.
abstract: Race-specific disease resistance in plants depends on the presence of resistance (R) genes. Most R genes encode NB-ARC-LRR proteins that carry a C-terminal leucine-rich repeat (LRR). Of the few proteins found to interact with the LRR domain, most have proposed (co)chaperone activity. Here, we report the identification of RSI2 (Required for Stability of I-2) as a protein that interacts with the LRR domain of the tomato R protein I-2. RSI2 belongs to the family of small heat shock proteins (sHSPs or HSP20s). HSP20s are ATP-independent chaperones that form oligomeric complexes with client proteins to prevent unfolding and subsequent aggregation. Silencing of RSI2-related HSP20s in Nicotiana benthamiana compromised the hypersensitive response that is normally induced by auto-active variants of I-2 and Mi-1, a second tomato R protein. As many HSP20s have chaperone properties, the involvement of RSI2 and other R protein (co)chaperones in I-2 and Mi-1 protein stability was examined. RSI2 silencing compromised the accumulation of full-length I-2 in planta, but did not affect Mi-1 levels. Silencing of heat shock protein 90 (HSP90) and SGT1 led to an almost complete loss of full-length I-2 accumulation and a reduction in Mi-1 protein levels. In contrast to SGT1 and HSP90, RSI2 silencing led to accumulation of I-2 breakdown products. This difference suggests that RSI2 and HSP90/SGT1 chaperone the I-2 protein using different molecular mechanisms. We conclude that I-2 protein function requires RSI2, either through direct interaction with, and stabilization of I-2 protein or by affecting signalling components involved in initiation of the hypersensitive response.
authors.affiliation: Department of Plant Pathology, Swammerdam Institute for Life Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Gerben
authors.initials: G
authors.lastname: Van Ooijen
authors.forename: Ewa
authors.initials: E
authors.lastname: Lukasik
authors.forename: Harrold A
authors.initials: HA
authors.lastname: Van Den Burg
authors.forename: Jack H
authors.initials: JH
authors.lastname: Vossen
authors.forename: Ben J C
authors.initials: BJ
authors.lastname: Cornelissen
authors.forename: Frank L W
authors.initials: FL
authors.lastname: Takken
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005670:Fusarium / Q000502:physiology; D020868:Gene Silencing; D050886:HSP20 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D054884:Host-Pathogen Interactions; D007113:Immunity, Innate; D000090263:Leucine-Rich Repeat Proteins; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D055550:Protein Stability; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D020798:Two-Hybrid System Techniques
chemical_list: D004268:DNA-Binding Proteins; D050886:HSP20 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; C106157:I2C protein, Lycopersicon esculentum; D000090263:Leucine-Rich Repeat Proteins; D010940:Plant Proteins; D011506:Proteins