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====== The Type III Effector XopJ1 from //Xanthomonas// ======

Author: [[https://www.researchgate.net/profile/Jens_Boch|Jens Boch]]\\
Internal reviewer: [[https://www.researchgate.net/profile/Joana_Costa12|Joana Costa]]\\
Expert reviewer: [[https://www.researchgate.net/profile/Frederik_Boernke|Frederik Börnke]]

Class: XopJ\\
Family: XopJ1\\
Prototype: XCV2156 (//Xanthomonas euvesicatoria// pv. //euvesicatoria//, ex //Xanthomonas campestris// pv. //vesicatoria//; strain 85-10)\\
GenBank ID: [[https://www.ncbi.nlm.nih.gov/protein/CAJ23833.1|CAJ23833]] (373 aa)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_011347382.1|WP_011347382.1]] (373 aa)\\
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. //vesicatoria// (//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).
=== Regulation ===

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

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).
=== Localization ===

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).
===== Conservation =====

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).
===== References =====

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: [[https://doi.org/10.1094/MPMI-22-6-0655|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: [[https://doi.org/10.1128/JB.185.24.7092-7102.2003|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: [[https://doi.org/10.1046/j.1365-2958.2001.02567.x|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: [[https://doi.org/10.1094/MPMI-06-17-0138-R|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: [[https://doi.org/10.1094/MPMI-20-10-1250|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: [[https://doi.org/10.1371/journal.ppat.1003427|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: [[https://doi.org/10.3389/fpls.2015.00599|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: [[https://doi.org/10.3389/fpls.2014.00736|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: [[https://doi.org/10.1104/pp.15.00132|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: [[https://doi.org/10.1111/J.1364-3703.2009.00590.X|10.1111/J.1364-3703.2009.00590.X]]

===== Acknowledgements =====

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