Molecular analysis of avirulence gene avrRpt2 and identification of a putative regulatory sequence common to all known Pseudomonas syringae avirulence genes

Abstract

The avrRpt2 locus from Pseudomonas syringae pv. tomato causes virulent strains ofP. syringae to be avirulent on some, but not all, lines ofAabidopsis thaliana and Glycine mar (soybean). We determined the DNA sequence of the avrRpt2 locus and identified the avrRpt2 gene as a 768-bp open reading frame encoding a putative 28.2-kDa protein. Deletion analysis and transcription studies provided further evidence that this open reading frame encodes AvrRpt2. We found that the avrRpt2 gene also has avirulence activity in P. syringae pathogens of Phaseous vulgaris (common bean), suggesting that disease resistance genes specific to avrRpt2 are functionally conserved among diverse plant species. The predicted AvrRpt2 protein is hydrophilic and contains no obvious membrane-spanning domains or export signal sequences, and there was no significant similarity of AvrRpt2 to sequences in the GenBank, EMBL, or Swiss PIR data bases. A comparison of the avrRpt2 DNA sequence to nine other P. syringac avinlence genes revealed a highly conserved sequence, GGAACCNA-N14-CCACNNA, upstream of the translation initiation codon. This motif is located 6 to 8 nucleotides upstream of the transcription start site in all four P. syringae avirulence genes for which a transcription start site has been determined, suggesting a role as a binding site for a novel form of RNA polymerase. Regulation ofavrRpt2 was similar to other P. syrmigae avirulence genes; expression was high in minimal medium and low in rich medium and depended on the hrpRS locus and an additional locus at the opposite end of the hrp cluster of P. syringae pv. tomato.

Virulence of the Phytopathogen Pseudomonas syringae pv. Maculicola Is rpoN Dependent

“…In the accompanying study (23), we demonstrate that rpoN in ES4326 is required for the expression of hrpL, which encodes an alternative sigma factor and is required for expression of the ES4326 hrp genes and avrRpt2 (12,17,29,97). We also show that constitutive expression of hrpL on plasmid pHRPLC restores the ability of ES4326 rpoN::Km r to elicit disease symptoms in A. thaliana and an HR in tobacco.…”

“…In the absence of a corresponding R gene product, the avr product enhances virulence; however, in hosts which have the corresponding R gene, recognition of the avr gene product enhances host resistance. Interestingly, most avr genes are also coordinately regulated with genes in the hrp cluster (27,29,46,67,71,77,97).…”

“…In the absence of a corresponding R gene product, the avr product enhances virulence; however, in hosts which have the corresponding R gene, recognition of the avr gene product enhances host resistance. Interestingly, most avr genes are also coordinately regulated with genes in the hrp cluster (27,29,46,67,71,77,97).The HR is accompanied by the induction of defense-related genes (7, 91) that are differentially expressed depending on the particular pair of avr and R gene products eliciting the HR (70, 72). Defense gene induction also occurs in the absence of the HR during compatible pathogen-host interactions, although usually later and at lower levels than those occurring during an HR (11,32,66).…”

Electrophysiological Characterization of the Arabidopsis avrRpt2-Specific Hypersensitive Response in the Absence of Other Bacterial Signals

“…As expected, dex-treated transgenic RPS2 seedlings produced a large amount of AvrRpt2, in contrast to solvent ethanol-treated seedlings. The mature AvrRpt2 protein is predicted to be 28.2 kD in size (Innes et al, 1993). However, AvrRpt2 is processed in planta to a 22-kD form, and an additional smaller band of approximately 21 kD is sometimes detected (McNellis et al, 1998;Mudgett and Staskawicz, 1999;Jin et al, 2003).…”

The Transcriptional Innate Immune Response to flg22. Interplay and Overlap with Avr Gene-Dependent Defense Responses and Bacterial Pathogenesis

“…Bacterial Avr proteins are translocated into the host cells through a type III protein secretion system (Galan and Collmer, 1999) which, in the case of Pseudomonas syringae DC3000, is thought to deliver more than 30 effector proteins (Boch et al, 2002;Collmer et al, 2002;Fouts et al, 2002;Guttman et al, 2002;Petnicki-Ocwieja et al, 2002;Zwiesler-Vollick et al, 2002). AvrRPM1 and AvrRpt2 from P. syringae provide examples of such type III effector proteins that are recognized by the products of the RPM1 and RPS2 resistance genes, respectively (Dangl et al, 1992;Innes et al, 1993). This recognition initiates the plant HR response through modification or loss of the host RIN4 protein (Mackey et al, 2002;Mackey et al, 2003;Axtell and Staskawicz, 2003).…”