Molecular recognition of pathogen attack occurs inside of plant cells in plant disease resistance specified by the Arabidopsis genes RPS2  and  RPM1

Abstract

The Arabidopsis thaliana disease resistance genes RPS2 and RPM1 belong to a class of plant disease resistance genes that encode proteins that contain an Nterminal tripartite nucleotide binding site (NBS) and a Cterminal tandem array of leucine-rich repeats. RPS2 and RPM1 confer resistance to strains of the bacterial phytopathogen Pseudomonas syringae carrying the avirulence genes avrRpt2 and avrB, respectively. In these gene-for-gene relationships, it has been proposed that pathogen avirulence genes generate specific ligands that are recognized by cognate receptors encoded by the corresponding plant resistance genes. To test this hypothesis, it is crucial to know the site of the potential molecular recognition. Mutational analysis of RPS2 protein and in vitro translation͞translocation studies indicated that RPS2 protein is localized in the plant cytoplasm. To determine whether avirulence gene products themselves are the ligands for resistance proteins, we expressed the avrRpt2 and avrB genes directly in plant cells using a novel quantitative transient expression assay, and found that expression of avrRpt2 and avrB elicited a resistance response in plants carrying the corresponding resistance genes. This observation indicates that no bacterial factors other than the avirulence gene products are required for the specific resistance response as long as the avirulence gene products are correctly localized. We propose that molecular recognition of P. syringae in RPS2-and RPM1-specified resistance occurs inside of plant cells.In plants, robust defense responses to invading phytopathogens often conform to a gene-for-gene relationship: resistance to a pathogen is only observed when the pathogen carries a specific avirulence (avr) gene and the plant carries a corresponding resistance (R) gene (1-3). Because avr-R gene-forgene relationships are observed in many plant-pathogen systems and are accompanied by a characteristic set of defense responses, a common molecular mechanism underlying avr-R gene mediated resistance has been postulated (4). One simple model which explains gene-for-gene relationships is that pathogen avr genes directly or indirectly generate a specific molecular signal (ligand) that is recognized by cognate receptors encoded by plant R genes. Recent cloning of plant resistance genes and corresponding pathogen avirulence genes provided the tools for a direct test of this ligand-receptor model (5).In the phytopathogenic interaction between the small flowering plant Arabidopsis thaliana and the bacterial phytopathogen Pseudomonas syringae, two R genes, RPS2 (6, 7) and RPM1 (8), and three corresponding avr genes, avrRpt2 (9), avrRpm1 (10), and avrB (11), have been isolated. RPS2 confers resistance to P. syringae strains expressing avrRpt2 (12, 13) and RPM1 confers resistance to P. syringae expressing avrRpm1 (14) or avrB (15). RPS2 and RPM1 belong to a major class of plant resistance genes which encode proteins containing nucleotide binding sites (NBS) and leucine-rich repeats (LRR) and which confer ...

A secreted Salmonella protein with homology to an avirulence determinant of plant pathogenic bacteria

“…Effector proteins secreted via type III secretion systems are thought to get translocated inside the target host cell where they are expected to stimulate or modulate host cellular functions (23,(30)(31)(32)(33)(34)(35)(36). We therefore investigated the translocation of AvrA into cultured intestinal Henle-407 cells infected with wild-type S. typhimurium using two complementary approaches.…”

The coat protein of tobamovirus acts as elicitor of both L 2 and L 4 gene-mediated resistance in Capsicum

“…The transient expression assay employed here has been used successfully for the functional analysis of avr genes from bacteria (Gopalan et al, 1996;Leister et al, 1996), fungi (Jia et al, 2000) and viruses (Gilardi et al, 1998).…”

The hypersensitive response and the induction of cell death in plants

“…Recent evidence indicates that there is such a direct interaction between the tomato Pto resistance gene product and the product of the avirulence gene avrPto from Pseudomonas syringae pv tomato (Scofield et al, 1997;Tang et al, 1997). To date, the analysis of the sequences of the different cloned resistance genes suggests that this possible type of direct interaction may not only happen in the plasma membrane but also in the cytoplasm (Jones, 1997) and in the nucleus (Leister et al, 1996;Van den Ackerveken et al, 1996).…”