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Bacterial virulence factors

Plant resistance genes

Molecular Diagnosis and Diversity for Regulated Xanthomonas

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Author: Jens Boch
Internal reviewer: Joana Costa
Expert reviewer: Frederik Börnke

Class: XopJ
Family: XopJ1
Prototype: XCV2156 (Xanthomonas euvesicatoria pv. euvesicatoria, ex Xanthomonas campestris pv. vesicatoria; strain 85-10)
RefSeq ID: CAJ23833 (373aa)
3D structure: Unknown

Biological function

How discovered?

XopJ was initially discovered as a HrpG-induced gene in a cDNA-AFLP screen in Xanthomonas campestris pv. vescicatoria (Xcv) and identified as a homolog to YopJ from Yersinia pestis (Noël et al., 2001). XopJ was later studied in more detail (Noël et al., 2003).

(Experimental) evidence for being a T3E

A chimeric protein consisting of the 155 N-terminal amino acids of XopJ fused to an N-terminally truncated AvrBs3 is secreted out of the bacterial cell and elicits a hypersensitive response in a Bs3 pepper plant. Secretion and translocation are dependent on components of the Xcv type III secretion system (hrcV) and translocon (hrpF) (Noël et al., 2003). The first 50 amino acids of XopJ are sufficient and the amino acids 2-8 required for secretion (Scheibner et al., 2018). This minimal secretion signal is not required for the interaction of XopJ with the effector chaperone HpaB or HrcQ from the bacterial type III secretion system (Scheibner et al., 2018).


xopJ is expressed in a hrpG- and hrpX-dependent manner (Noël et al., 2001; Noël et al., 2003).


Although a frameshift mutation of xopJ did not affect pathogenicity or bacterial growth in plants in early experiments (Noël et al., 2003), later studies showed that a xopJ mutant is slightly impaired in growth in pepper in late stages of the infection (Üstun et al., 2013). XopJ also suppresses tissue necrosis during Xcv infection of its susceptible host plant pepper. XopJ further suppresses defence-related callose deposition and secretion of extracellular proteins (secGFP) from the plant cell (Bartetzko et al., 2009). The XopJ protein interacts with the proteasomal subunit Regulatory Particle AAA-ATPase6 (RPT6) from the 26S proteasome in yeast and in planta and recruits RPT6 to the plant plasma membrane which leads to inhibition of the proteasome activity. For this activity, the myristoylation sequence and the catalytic triad are required (Üstün et al., 2013). The ability of XopJ to inhibit the proteasome is directly related to its function in cell death suppression. The interaction of XopJ with RPT6 leads to degradation of the latter, which depends on the XopJ catalytic Cys residue indicating that XopJ acts as protease (Üstun & Börnke, 2015). The inhibition of proteasome activity results in the inhibition of NPR1 turnover and subsequent salicylic acid-related immune responses (Üstün et al., 2013; Üstün & Börnke, 2015). The degradation of RPT6 is dependent on the Walker B motif (ATP hydrolysis) of RPT6 (Üstün & Börnke, 2015). Furthermore, the Agrobacterium-mediated expression of xopJ triggers a cell death reaction in Nicotiana clevelandii. Membrane localization of XopJ is required for this (Thieme et al., 2007). The Agrobacterium-mediated expression of xopJ in Nicotiana benthamiana can also trigger cell death, but only if salicylic acid is applied simultaneously (Üstün et al., 2015). This reaction was dependent on SGT1, NDR1, and NPR1, but EDS1-independent (Üstün et al., 2015). It is suggested that XopJ is recognized by a CC-NBS-LRR resistance protein in N. benthamiana (Üstun et al., 2015). It has been proposed that in essence, XopJ acts as a tolerance factor which attenuates the accumulation of salicylic acid in infected plant tissue to delay host tissue necrosis in a proteasome-dependent manner (Üstün et al., 2015; Üstün & Börnke, 2014).


XopJ carries a predicted N-myristoylation motif on a glycine residue at position two of the polypeptide. Following type III translocation, XopJ localizes to the plant plasma membrane via N-terminal myristoylation by the host cell (Thieme et al., 2007; Bartetzko et al., 2009). Mutation of the glycine residue at postion two into alanine (G2A) renders the protein soluble. A wildtype XopJ-GFP fusion (not a mutant in the catalytic triad) also localizes to vesicle-like structures that colocalize with Golgi-marker proteins.

Enzymatic function

XopJ belongs to the group of YopJ-family effectors and is a member of the YopJ/AvrRxv family of SUMO peptidases and acetyltransferases. These are characterized as C55 cysteine proteases, ubiquitin-like proteases (deSUMOylation), or acetyltransferases. Such enzymes share a characteristic catalytic triad consisting of the amino acids histidine, glutamic or aspartic acid, and cysteine. XopJ has Cys protease activity in vitro and in vivo, but seems to lack acetyltransferase activity under standard assay conditions (Üstün & Börnke, 2015).

Interaction partners

19S RP subunit RPT6 (RP ATPase 6) of the 26S proteasome (Üstün & Börnke, 2015). The interaction is dependent on the Walker A motif (ATP binding) of RPT6. The interaction between the two proteins has been shown by yeast two-hybrid assays, in vivo and in vitro pull-down, as well as by bimolecular fluorescence assays in planta (Üstün et al., 2013).


XopJ belongs to the broadly occurring YopJ-effector family of cysteine proteases/acetyltransferases including XopJ, AvrRxv, AvrXx4, AvrBsT which have somewhat related, but distinct activities. Distantly related members occur in plant and animal pathogenic bacteria.

In xanthomonads

Yes (e.g., X. campestris pv. vesicatoria, X. campestris pv. malvacearum, not in X. oryzae or X. citri) (White et al., 2009).

In other plant pathogens/symbionts

Yes (e.g., many Pseudomonas spp. (HopZ-family), Ralstonia solanacearum (PopP1), Acidovorax citrulli, Bradyrhizobium sp., Mesorhizobium sp., Sinorhizobium fredii) (Noël et al., 2001).


Bartetzko V, Sonnewald S, Vogel F, Hartner K, Stadler R, Hammes UZ, Börnke F (2009). The Xanthomonas campestris pv. vesicatoria type III effector protein XopJ inhibits protein secretion: evidence for interference with the cell wall-associated defense responses. Mol. Plant Microbe Interact. 22: 655-664. DOI: 10.1094/MPMI-22-6-0655

Noël L, Thieme F, Gäbler J, Büttner D, Bonas U (2003). XopC and XopJ, two novel type III effector proteins from Xanthomonas campestris pv. vesicatoria. J. Bacteriol. 185: 7092-7102. DOI: 10.1128/JB.185.24.7092-7102.2003

Noël L, Thieme F, Nennstiel D, Bonas U (2001). cDNA-AFLP analysis unravels a genome-wide hrpG-regulon in the plant pathogen Xanthomonas campestris pv. vesicatoria. Mol. Microbiol. 41: 1271-1281. DOI: 10.1046/j.1365-2958.2001.02567.x

Scheibner F, Hartmann N, Hausner J, Lorenz C, Hoffmeister AK, Büttner D (2018). The type III secretion chaperone HpaB controls the translocation of effector and noneffector proteins from Xanthomonas campestris pv. vesicatoria. Mol. Plant Pathogen Interact. 31: 61-74. DOI: 10.1094/MPMI-06-17-0138-R

Thieme F, Szczesny R, Urban A, Kirchner O, Hause G, Bonas U (2007). New type III effectors from Xanthomonas campestris pv. vesicatoria trigger plant reactions dependent on a conserved N-myristoylation motif. Mol. Plant Microbe Interact. 20: 1250-1261. DOI: 10.1094/MPMI-20-10-1250

Üstün S, Bartetzko V, Börnke F (2013). The Xanthomonas campestris type III effector XopJ targets the host cell proteasome to suppress salicylic-acid mediated plant defence. PLoS Pathog. 9: e1003427. DOI: 10.1371/journal.ppat.1003427

Üstün S, Bartetzko V, Börnke F (2015). The Xanthomonas effector XopJ triggers a conditional hypersensitive response upon treatment of N. benthamiana leaves with salicylic acid. Front. Plant Sci. 6: 599. DOI: 10.3389/fpls.2015.00599

Üstün S, Börnke F (2014). Interactions of Xanthomonas type-III effector proteins with the plant ubiquitin and ubiquitin-like pathways. Front. Plant Sci. 5: 736. DOI: 10.3389/fpls.2014.00736

Üstün S, Börnke F (2015). The Xanthomonas campestris type III effector XopJ proteolytically degrades proteasome subunit RPT6. Plant Physiol. 168: 107-119. DOI: 10.1104/pp.15.00132

White F, Potnis N, Jones JB, Koebnik R (2009). The type III effectors of Xanthomonas. Mol. Plant Pathol. 10: 749-766. DOI: 10.1111/J.1364-3703.2009.00590.X

bacteria/t3e/xopj1.txt · Last modified: 2020/09/21 18:15 by rkoebnik