Abstract
Pepper plants (Capsicum annuum) containing the Bs2 resistance gene are resistant to strains of Xanthomonas campestris pv vesicatoria (Xcv) expressing the bacterial effector protein AvrBs2. AvrBs2 is delivered directly to the plant cell via the type III protein secretion system (TTSS) of Xcv. Upon recognition of AvrBs2 by plants expressing the Bs2 gene, a signal transduction cascade is activated leading to a bacterial disease resistance response. Here, we describe a novel pathosystem that consists of epitope-tagged Bs2-expressing transgenic Nicotiana benthamiana plants and engineered strains of Pseudomonas syringae pv tabaci that deliver the effector domain of the Xcv AvrBs2 protein via the TTSS of P. syringae. This pathosystem has allowed us to exploit N. benthamiana as a model host plant to use Agrobacterium tumefaciens-mediated transient protein expression in conjunction with virus-induced gene silencing to validate genes and to identify protein interactions required for the expression of plant host resistance. In this study, we demonstrate that two genes, NbSGT1 and NbNPK1, are required for the Bs2/AvrBs2-mediated resistance responses but that NbRAR1 is not. Protein localization studies in these plants indicate that full-length Bs2 is primarily localized in the plant cytoplasm. Three protein domains of Bs2 have been identified: the N terminus, a central nucleotide binding site, and a C-terminal Leu-rich repeat (LRR). Co-immunoprecipitation studies demonstrate that separate epitope-tagged Bs2 domain constructs interact in trans specifically in the plant cell. Co-immunoprecipitation studies also demonstrate that an NbSGT1-dependent intramolecular interaction is required for Bs2 function. Additionally, Bs2 has been shown to associate with SGT1 via the LRR domain of Bs2. These data suggest a role for SGT1 in the proper folding of Bs2 or the formation of a Bs2-SGT1-containing protein complex that is required for the expression of bacterial disease resistance.
MeSH Terms
Arabidopsis Proteins/metabolism
Cell Cycle Proteins/genetics,metabolism
Cytoplasm/metabolism
Epitopes/metabolism
Genetic Vectors/genetics
Immunity, Innate/genetics
MAP Kinase Kinase Kinases/genetics,metabolism
Macromolecular Substances/metabolism
Molecular Chaperones/genetics,metabolism
Molecular Sequence Data
Plant Proteins/genetics,metabolism
Plants, Genetically Modified/genetics,metabolism,microbiology
Protein Binding/physiology
Protein Folding
Protein Structure, Tertiary/genetics
Pseudomonas syringae/genetics,metabolism
Tobacco/genetics,metabolism,microbiology
Chemicals
Arabidopsis Proteins
BS2 protein, Capsicum chacoense
Cell Cycle Proteins
Epitopes
Macromolecular Substances
Molecular Chaperones
Plant Proteins
SGT1a protein, Arabidopsis
MAP Kinase Kinase Kinases
NPK1 protein, Nicotiana tabacum
Authors & Affiliations
6 authors, click to expand affiliations / ORCID
Leister R Todd
Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102, USA.
Dahlbeck Douglas
Day Brad
Li Yi
Chesnokova Olga
Staskawicz Brian J
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