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 AvrPphF Pseudomonas syringae pv. phaseolicola Interferes with the plant defense responseNK AvrRpt2 Pseudomonas syringae pv. tomato Interferes with the plant defense responseNK AvrRpm1 Pseudomonas syringae pv. maculicola Enhances growthPlasma membrane [ NK Plasma membrane AvrPto Pseudomonas syringae pv. tomato Enhances growth Degradation of resistance gene Plasma membrane NoNK AvrBst Xanthomonas campestris pv. campestris Ubiquitin-like proteaseNK YesNK AvrXa7 Xanthomonas oryzae pv. oryzae Transcriptional activation domain required for virulence NucleusYesNK 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] [53] Nucleus 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 Product Promotes Pathogen Virulence from Inside Plant Cells. Molecular Plant-Microbe Interactions Vol. 13: 1312–1321

Virulence genes suppress avr/R gene interactions Chen 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

avrRpm1 N-terminal fatty acylation sequence avrRpm1 MGCVSSTSR Soc3a MGCSVSKKK Ca sensor G2A = glycine change to alanine Loss 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

AvrXa7 : a nuclear targeted protein PX086mx53 = NLS - version Resistant Susceptible NORMAL avrXa7 express avrXa7 NLS- avrXa7 over express NORMAL avrXa7 express avrXa7 NLS- avrXa7 over express Fig. 1. AvrXa7 is a DNA-binding protein. Double-stranded oligonucleotides were end labeled with 32 P, 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