Recent advances in understanding

gene –for – gene interactions

Avr Protein    

Pathogen     Homology with and/or possible virulence function     

Location in the plant cell

Common domain for avirulence and virulence function    

Location of the matching R gene      AvrPphC     Pseudomonas

syringae pv. phaseolicola    

Interferes with the plant defense response

NK ‡     NK     NK    

AvrPphF     Pseudomonas

syringae pv. phaseolicola    

Interferes with the plant defense response NK     NK     NK    

AvrRpt2     Pseudomonas

syringae pv. tomato    Interferes with the plant defense response NK     NK     NK    

AvrRpm1    

Pseudomonas syringae pv. maculicola    

Enhances growth Plasma membrane [

NK     Plasma membrane

AvrPto     Pseudomonas

syringae pv. tomato    Enhances growthDegradation of resistance gene     

Plasma membrane

No NK    

AvrBst     Xanthomonas

campestris pv. campestris    

Ubiquitin-like protease NK     Yes NK    

AvrXa7     Xanthomonas oryzae

pv. oryzae    Transcriptional activation domain required for virulence

Nucleus Yes NK    

AvrBs2     Xanthomonas

campestris pv. vesicatoria    

Agrocinopine synthase (from Agrobacterium tumefaciens)    

NK     Recognition region localized in the portion with highest homology to synthase

NK    

AvrBs3     Xanthomonas

campestris pv. glycinea    

Transcriptional activation domain required for virulence  

Nucleus    Yes   NK    

PthA     Xanthomonas citri     Transcriptional activation domain required for

virulence/causes cell hyperplasia [53]    Nucleus     NK     NK    

Avr9     Cladosporium

fulvum    NK     Exoplasmic     NK     External plasma

membrane    

Avirulence Gene Function – what is currently known

Avirulence genes promote virulence

Disease symptoms and growth of Pseudomonas syringae pv. tomato strain DC3000 (PstDC3000) on Arabidopsis thaliana leaf tissue.

A, Diseasesymptoms caused by PstDC3000 on A. thaliana No-0 rps2 (top) and Col-0 rps2 (bottom) plants. Leaves are shown 4 days after inoculation with PstDC3000

(left) and PstDC3000(avrRpt2) (right). Plants were inoculated by dipping them into bacterial suspensions (3 to 5 × 10 8 CFU/cm 2 ) containing the surfactant Silwet L-77. B, Growth of PstDC3000 and PstDC3000(avrRpt2) in leaf tissue of Col-0 rps2, No-0 rps2, and No-0 RPS2 plants.. In B, A. thaliana plants were inoculated by

vacuum infiltration with the indicated PstDC3000 strains at an initial density of 1 × 10 5 CFU/cm 2 . The concentration of bacteria in the plant leaves was assayed after 0,

2, and 4 days. Datapoints represent means of three independent determinations ± standard error of the mean. Experiments presented in A, B, were carried out a minimum of three times with similar results

Chen et al., (2000) The Pseudomonas syringae avrRpt2 Gene ProductPromotes Pathogen Virulence from Inside Plant Cells. Molecular Plant-Microbe Interactions Vol. 13: 1312–1321

Virulence genes suppress avr/R gene interactionsChen et al., (2000) The Pseudomonas syringae avrRpt2 Gene Product

Promotes Pathogen Virulence from Inside Plant Cells. Molecular Plant-Microbe Interactions Vol. 13: 1312–1321

RPM1::MYC is a peripheral PM protein.

Fractionation of RPM1::MYC on sucrose gradients. A 12-55% (wt/vol) linear sucrose gradient was used to fractionate total extract from transgenic plants. Aliquots of each fraction were blotted to nitrocellulose and were analyzed with either anti-c-Myc or the subcellular compartment marker antibodies listed at the right of each panel.

C-Myc epitope has been “artificially” added to RPM1

Plasma Membrane

Cytoplasm and ER

Anti-myc antibody can be used to detect myc-labelled RPM1

Boyes et al., (1998) The Arabidopsis thaliana RPM1 disease resistance gene product is a peripheral plasma membrane protein that is degraded coincident with the hypersensitive response. 95, PNAS USA 15849-15854

avrRpm1 N-terminal fatty acylation sequence

avrRpm1 MGCVSSTSRSoc3a MGCSVSKKKCa sensor

G2A = glycine change to alanineLoss in avirulence

AvrRpm1 and avrB localise to the plant cell membrane.

Protoplasts from rpm1 plants were transformed with plasmid that express either avr-GFP or avrG2A-GFP constructs. Control transformations were with GFP alone.

RPM1::MYC is degraded after inoculation with avirulent P. syringae isolates, which trigger LZ-NBS-LRR resistance genes

Hours post inoculation

Boyes et al., (1998) The Arabidopsis thaliana RPM1 disease resistance gene product is a peripheral plasma membrane protein that is degraded coincident with the hypersensitive response. 95, PNAS USA 15849-15854

AvrXa7 : a nuclear targeted protein

PX086mx53 = NLS- version

Resistant

Susceptible

NORMALavrXa7express

avrXa7NLS-

avrXa7over

express

NORMALavrXa7express

avrXa7NLS-

avrXa7over

express

Fig. 1.   AvrXa7 is a DNA-binding protein. Double-stranded oligonucleotides were end labeled with 32P, mixed with AvrXa7 or GST (glutathione S-transferase), and subjected to polyacrylamide electrophoresis. Arrow indicates position of well.

Yang et al., (2000) The virulence factor AvrXa7 of Xanthomonas oryzae pv. oryzae is a type III secretion pathway-dependent nuclear-localized double-stranded DNA-binding protein.Proc Natl Acad Sci U S A 15;:9807

“Guard” Hypotheses