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Bacterial virulence factors

Plant resistance genes

Molecular Diagnosis and Diversity for Regulated Xanthomonas

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This DokuWiki is based upon work from COST Action CA16107 EuroXanth, supported by COST (European Cooperation in Science and Technology)

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Author: Mariya Stoyanova
Internal reviewer: Yael Helman
Expert reviewer: FIXME

Class: AvrBs1
Family: AvrBs1
Prototype: AvrBs1 (Xanthomonas euvesicatoria pv. euvesicatoria, ex Xanthomonas campestris pv. vesicatoria; strain E3) (Swanson et al., 1988)
RefSeq ID: CAJ19916.1 (445 aa)
3D structure: Q3C000_XANC5 (homology model)

Biological function

How discovered?

Dahlbeck and Stall (1979) demonstrated that pepper race 2 strains of X. campestris pv. vesicatoria (Xcv) spontaneously mutate from avirulence to virulence (race 1) at a high frequency (4×10-4 per cell per division) when inoculated into a pepper cultivar containing the Bs1 locus. Later, avirulence loci were found to be located in a plasmid during trials to transmit the copper resistence loci by conjugation (Stall et al., 1986). In further studies an avirulence gene in race 2 strains was cloned and molecularly characterized by restriction enzyme mapping, subcloning and deletion analysis. The gene, avrBs1, was localized to a 5.3-kb fragment of DNA, located in the self-transmissible copper resistance plasmid pXvCu1. A single cosmid clone, pXv2000, was identified to specifically convert virulent race 1 isolates of Xcv to avirulence when inoculated into the pepper cultivar ECW10R containing the dominant resistance gene Bs1. It was demonstrated that the cloned wild type avirulence gene avrBs1, which encodes encodes a 50-kD protein, can complement race 2 spontaneous race-change mutants (Ronald & Staskawicz, 1988; Swanson et al., 1988).

(Experimental) evidence for being a T3E

Epitope tagged AvrBs1 proteins were detected in culture supernatants only in the presence of a functional type III apparatus and not in a hrcV mutant, showing that the AvrBs1 proteins are secreted by Xcv in an hrp-dependent manner (Escolar et al., 2001).


In 2001, in tests whether avrBs1 promoter activity depends on the hrp regulatory genes, hrpG and hrpX, promoter constructs containing only avrBs1 ORF2 were conjugated into wild-type Xcv race 2 strains deleted in hrpX or hrpG. The mutations did not significantly alter the GUS activity, indicating that avrBs1 expression is not under the control of these hrp gene regulators (Escolar et al., 2001). However, gene expression analysis using β-glucuronidase as reporter in another study in 2006 showed 7.3-fold reduction in GUS activity indicating that avrBs1 was regulated by hrpG (Rongqi et al., 2006). In 2010 it was reported that AvrBsT suppresses AvrBs1-elicited HR from X. campestris pv. vesicatoria in resistant pepper plants. HR suppression occurs inside the plant cell and depends on a conserved predicted catalytic residue of AvrBsT (Szczesny et al., 2010).


AvrBs1 specifies avirulence on pepper cultivars containing the resistance gene Bs1 observed as hypersensitive response (HR) induction (Ronald & Staskawicz, 1988). Transient expression of avrBs1 and avrBsT in resistant host plants using Agrobacterium tumefaciens-mediated gene transfer resulted in the induction of a specific HR (Escolar et al., 2001). Studies with expression of avrBs1 in N. benthamiana showed a decrease in the starch content in chloroplasts and an increased number of vesicles, indicating an enlargement of the central vacuole and the cell wall. These changes resulted in a swelling of the upper epidermis and bloating of the palisade cells in the mesophyll, thus changing their shape and leading to a decrease in the intercellular spaces. A significant increase in ion leakage, as well as dead cells in avrBs1-expressing tissue were also detected. Macroscopically, chlorosis and weak necrotic reactions in N. benthamiana were observed (Gürlebeck et al., 2009).


AvrBs1-GFP localizes exclusively to the cytoplasm of the plant cells (Gürlebeck et al., 2009).

Enzymatic function

Unknown. It was found that AvrBs1 suppresses the activation of the high osmolarity glycerol (HOG) MAP kinase pathway in yeast, suggesting that this effector targets a signaling component that is conserved in eukaryotic organisms (Teper et al., 2015).

Interaction partners

Gene silencing experiments revealed that SNF1-related kinase 1 (SnRK1) is required for the induction of the AvrBs1-specific HR. It was speculated that SnRK1 is involved in the AvrBsT-mediated suppression of the AvrBs1-specific HR (Szczesny et al., 2010).


In xanthomonads:

Yes (X. campestris pv. campestris (Ronald & Staskawicz, 1988), X. campestris pv. vitians (Ronald & Staskawicz, 1988), X. arboricola pv. juglandis [Acc.No: SYZ61276.1] )

In other plant pathogens/symbionts:

Xylophilus ampelinus (Nyembe, 2014), Acidovorax citrulli, Pseudomonas amygdali [Acc.No: EGH05685.1] , homolog of AvrA from Pseudomonas syringae pv. glycinea (Napoli & Staskawicz, 1987; Ronald & Staskawicz, 1988).


Dahlbeck D, Stall RE (1979). Mutations for change of race in cultures of Xanthomonas vesicatoria. Phytopathology 69: 634-636. DOI: 10.1094/Phyto-69-634

Escolar L, Van Den Ackerveken G, Pieplow S, Rossier O, Bonas U (2001). Type III secretion and in planta recognition of the Xanthomonas avirulence proteins AvrBs1 and AvrBsT. Mol. Plant Pathol. 2: 287-296. DOI: 10.1046/j.1464-6722.2001.00077.x

Gürlebeck D, Jahn S, Gürlebeck N, Szczesny R, Szurek B, Hahn S, Hause G, Bonas U (2009). Visualization of novel virulence activities of the Xanthomonas type III effectors AvrBs1, AvrBs3 and AvrBs4. Mol. Plant Pathol. 10: 175-188. DOI: 10.1111/j.1364-3703.2008.00519.x

Napoli C, Staskawicz BJ (1987). Molecular characterization of an avirulence gene from race 6 of Pseudomonas syringae pv. glycinea. J. Bacteriol. 169: 572-578. DOI: 10.1128/jb.169.2.572-578.1987

Nyembe NPP (2014). Development of a reporter system for the analysis of Xylophilus ampelinus type III secreted effectors. Doctoral Thesis, University of the Western Cape, South Africa. PDF:

Ronald PC, Staskawicz BJ (1988). The avirulence gene avrBs1 from Xanthomonas campestris pv. vesicatoria encodes a 50-kD protein. Mol. Plant Microbe Interact. 1: 191-198. DOI: 10.1094/MPMI-1-191

Rongqi X, Xianzhen L, Hongyu W, Bole J, Kai L, Yongqiang H, Jiaxun F, Jiliang T (2006). Regulation of eight avr by hrpG and hrpX in Xanthomonas campestris pv. campestris and their role in pathogenicity. Progress in Natural Science 16: 1288-1294. DOI: 10.1080/10020070612330143

Stall RE, Loschke DC, Jones JB (1986). Linkage of copper resistance and avirulence loci on a self-transmissible plasmid in Xanthomonas campestris pv. vesicatoria. Phytopathology 76: 240-243. DOI: 10.1094/Phyto-76-240

Swanson J, Kearney B, Dahlbeck D, Staskawicz B (1988). Cloned avirulence gene of Xanthomonas campestris pv. vesicatoria complements spontaneous race-change mutants. Mol. Plant Microb. Interact. 1: 5-9. DOI: 10.1094/MPMI-1-005

Szczesny R, Büttner D, Escolar L, Schulze S, Seiferth A, Bonas U (2010). Suppression of the AvrBs1-specific hypersensitive response by the YopJ effector homolog AvrBsT from Xanthomonas depends on a SNF1-related kinase. New Phytol. 187: 1058-1074. DOI: 10.1111/j.1469-8137.2010.03346.x

Teper D, Sunitha S, Martin GB, Sessa G (2015). Five Xanthomonas type III effectors suppress cell death induced by components of immunity associated MAP kinase cascades. Plant Signal. Behav. 10: e1064573. DOI: 10.1080/15592324.2015.1064573

Thieme F, Koebnik R, Bekel T, Berger C, Boch J, Büttner D, Caldana C, Gaigalat L, Goesmann A, Kay S, Kirchner O, Lanz C, Linke B, McHardy AC, Meyer F, Mittenhuber G, Nies DH, Niesbach-Klösgen U, Patschkowski T, Ruckert C, Rupp O, Schneiker S, Schuster SC, Vorhölter FJ, Weber E, Pühler A, Bonas U, Bartels D, Kaiser O (2005). Insights into genome plasticity and pathogenicity of the plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria revealed by the complete genome sequence. J. Bacteriol. 187: 7254-7266. 10.1128/JB.187.21.7254-7266.2005

Further reading

Kearney B, Staskawicz BJ (1990). Characterization of IS476 and its role in bacterial spot disease of tomato and pepper. J. Bacteriol. 172: 143-148. DOI: 10.1128/jb.172.1.143-148.1990. Erratum in: J. Bacteriol. (1990) 172: 2199.

O'Garro LW, Gibbs H, Newton A (1997). Mutation in the avrBs1 avirulence gene of Xanthomonas campestris pv. vesicatoria influences survival of the bacterium in soil and detached leaf tissue. Phytopathology 87: 960-966. DOI: 10.1094/PHYTO.1997.87.9.960

bacteria/t3e/avrbs1.txt · Last modified: 2022/05/09 11:30 by rkoebnik