====== XopJ2 ======

Author: [[https://www.researchgate.net/profile/Daiva_Burokiene|Daiva Burokienė]]\\
Internal reviewer: [[https://www.researchgate.net/profile/Eran_Bosis|Eran Bosis]]\\
Expert reviewer: FIXME

Class: XopJ\\
Family: XopJ2\\
Prototype: AvrBsT (//Xanthomonas euvesicatoria// pv. //euvesicatoria//, ex //Xanthomonas campestris// pv. //vesicatoria//; strain 75-3)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_074052319.1|WP_074052319.1]] (350 aa)\\
Synonym: AvrBsT\\
3D structure: unknown

===== Biological function =====

=== How discovered? ===

The //avrBsT// avirulence gene was first identified in the XcvT race 1 strain 75-3, which is avirulent on the pepper cultivar ECW (Minsavage //et al//., 1990). The //avrBsT// gene was localized on an indigenous plasmid of approximately 41 kb in the XcvT race 1 strain 75-3 (Minsavage //et al//., 1990). Spontaneous loss of the plasmid-borne //avrBsT// allowed XcvT race 1 75-3 mutants to cause disease on normally resistant pepper lines, suggesting simple genetic control of nonhost, //avrBsT//-specific resistance (Minsavage //et al//., 1990). The //avrBsT// gene sequence was published in 1999 (Ciesiolka //et al//., 1999).
=== (Experimental) evidence for being a T3E ===

C-myc epitope-tagged AvrBsT protein was detected in culture supernatants of the //X. campestris// pv. //vesicatoria// (//Xcv//) strain 85* only in the presence of a functional type III apparatus and not in a //hrcV// mutant, showing that the protein is secreted in an hrp-dependent manner (Escolar //et al//., 2001). Transient expression of //avrBsT// in resistant host plants using //Agrobacterium tumefaciens//-mediated gene transfer resulted in the induction of a specific HR. This indicates that recognition occurs intracellularly, and suggested that during the Xcv infection, AvrBsT is translocated from //Xcv// into the plant cell (Escolar //et al//., 2001). Mutation studies of a putative translocation motif (TrM) showed that the proline/arginine-rich motif contributes to efficient type III-dependent secretion and translocation of AvrBsT and affects the dependence of AvrBsT transport on the general T3S chaperone HpaB (Prochaska //et al//., 2018).
=== Regulation ===

Expression of the //avrBsT// gene is constitutive and independent of the //hrp// gene regulators in //Xcv// strain 85-10, //hrpG// and //hrpX// (Escolar //et al//., 2001).
=== Phenotypes ===

  * AvrBsT was found to suppress the hypersensitive response (HR) that is elicited by the effector protein AvrBs1 from //Xcv//  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).
  * AvrBsT was found to act as a virulence factor in tomato plants (Kim //et al//., 2010).
  * Growth of //Xcv//  strain Ds1 ectopically expressing //avrBsT//  was significantly enhanced in tomato leaves, whereas growth of //Xcv//  strain Bv5-4a //ΔavrBsT//  was significantly reduced (Kim //et al//., 2010).
  * AvrBsT also significantly compromised callose deposition and defense-marker gene expression in tomato plants when inoculating //Xcv//  at high titer (Kim //et al//., 2010).
  * One out of 71 //Arabidopsis thaliana//  ecotypes, Pi-0, was found to recognize (HR) AvrBsT when delivered from //Xanthomonas campestris//  pv. //campestris//  (Cunnac //et al//., 2007). //Pseudomonas syringae//  pv. //tomato//  (//Pst//) strain DC3000 expressing a hybrid protein consisting of a //Pst//  T3S signal derived from AvrRpt2 fused to AvrBsT-HA (haemagglutinin epitope tag) elicited HR and limited pathogen growth, confirming that the HR leads to defense (Cunnac //et al//., 2007). Pi-0 leaves infected with //Pst//  DC3000 expressing a hybrid protein containing a mutation in the catalytic core did not trigger, indicating that the Pi-0 HR is triggered by the putative enzymatic activity of AvrBsT (Cunnac //et al//., 2007).
  * Resistance in Pi-0 was found to be caused by a recessive mutation predicted to inactivate a carboxylesterase known to hydrolyze lysophospholipids and acylated proteins in eukaryotes. Transgenic Pi-0 plants expressing the wild-type allele from the //A. thaliana//  ecotype Columbia were susceptible to //Pst//  DC3000 AvrRpt2-AvrBsT-HA infection. These data indicated that the carboxylesterase inhibits AvrBsT-triggered phenotypes in //Arabidopsis//, and the resistance gene was therefore called //SOBER1//  (Suppressor Of AvrBsT-Elicited Resistance 1), where the inactive allele in Pi-0, //sober1-1//, provides resistance (Cunnac //et al//., 2007).
  * It was later shown that Pi-0 leaves infected with //Pst//  DC3000 expressing AvrBsT accumulated higher levels of phosphatidic acid (PA) compared to leaves infected with //Pst//  DC3000. Phospholipase D (PLD) activity was required for high PA levels and AvrBsT-dependent HR in Pi-0. Overexpression of SOBER1 in Pi-0 reduced PA levels and inhibited HR. These data implicated PA, phosphatidylcholine (PC) and lysophosphatidylcholine (LysoPC) as potential SOBER1 substrates. Recombinant His<sub>6</sub>-SOBER1 hydrolyzed PC but not PA or LysoPC in vitro indicating that the enzyme has phospholipase A2 (PLA2) activity. Chemical inhibition of PLA2 activity in leaves expressing SOBER1 resulted in HR in response to Pst DC3000 AvrBsT. These data were consistent with the model that SOBER1 PLA2 activity suppresses PLD-dependent production of PA in response to AvrBsT elicitation (Kirik //et al//., 2009).
  * Transgenic //Arabidopsis//  plants overexpression AvrBsT upon dexamethasone (DEX) induction showed reduced susceptibility to infection with the obligate biotrophic oomycete //Hyaloperonospora arabidopsidis//  (Hwang //et al//., 2012). In contrast, plants overexpressing dexamethasone //(DEX)//://avrBsT//  exhibited enhanced susceptibility to //Pseudomonas syringae//  pv. //tomato//  (Pst) DC3000 infection (Hwang //et al//., 2012). Thus, AvrBsT overexpression leads to both disease and defense responses to microbial pathogens of different lifestyles (Hwang //et al//., 2012).
  * Phylogenomics revealed that a host-range expansion of //X. euvesicatoria//  pv. //perforans//  (//Xep//) field strains on pepper is due, in part, to a loss of the effector AvrBsT. Further studies with //Xep//  demonstrated that a double deletion of //avrBsT//  and //xopQ//  allowed a host range expansion for //Nicotiana benthamiana//  (Schwartz //et al//., 2015).
  * Later, AvrBsT was found to contribute to fitness of //Xep//  on tomato plants under field conditions (Abrahamian //et al//., 2018).

=== Localization ===

Transient coexpression of //CaHSP70a//  and //avrBsT//  under the control of the 35S promoter led to cytoplasmic localization of the CaHSP70a-AvrBsT complex and significantly enhanced //avrBsT//-triggered cell death in //Nicotiana benthamiana//  (Kim //et al//., 2015a).

=== Enzymatic function ===

AvrBsT belongs to the YopJ family, members of which were shown to act as cysteine proteases containing a catalytic triad (His, Glu, Cys). It was shown that AvrBsT requires a functional protease catalytic core to trigger defense responses in resistant plant cells, suggesting that AvrBsT acts as a protease to disrupt immune signaling pathways (Orth //et al//., 2000). AvrBsT was later shown to possess acetyltransferase activity and acetylates ACIP1 (for //ACETYLATED INTERACTING PROTEIN1//) from //Arabidopsis//. Genetic studies revealed that //Arabidopsis//  ACIP family members are required for both pathogen-associated molecular pattern (PAMP)-triggered immunity and AvrBsT-triggered ETI during //Pst//  DC3000 infection. Microscopy studies revealed that ACIP1 is associated with punctae on the cell cortex and some of these punctae co-localize with microtubules. Wild-type //Pst//  DC3000 or //Pst//  DC3000 AvrRpt2 infection triggered the formation of numerous, small ACIP1 punctae and rods. By contrast, //Pst//  DC3000 AvrBsT infection primarily triggered the formation of large GFP-ACIP1 aggregates, in an acetyltransferase-dependent manner. These data suggested that AvrBsT-dependent acetylation //in planta//  alters ACIP1’s defense function, which is linked to the activation of ETI (Cheong //et al//., 2014).

=== Interaction partners ===

  * Yeast two-hybrid based analyses identified a putative regulator of sugar metabolism, SNF1-related kinase 1 (SnRK1), as an interactor of AvrBsT (Szczesny //et al//., 2010). Gene silencing experiments revealed that SnRK1 is required for the induction of the AvrBs1-specific HR, which is suppressed by AvrBsT (Szczesny //et al//., 2010). Thus, SnRK1 may be involved in the AvrBsT-mediated suppression of the AvrBs1-specific HR (Szczesny //et al//., 2010).
  * Later, the pepper SGT1 (for suppressor of the G2 allele of //skp1//) and PIK1 (for receptor-like cytoplasmic kinase1) were identified as host interactors of AvrBsT. SGT1 forms a heterotrimeric complex with both AvrBsT and PIK1 exclusively in the cytoplasm. PIK1 specifically phosphorylates SGT1 and AvrBsT in vitro. AvrBsT binding to SGT1 resulted in the inhibition of PIK1-mediated SGT1 phosphorylation and subsequent nuclear transport of the SGT1-PIK1 complex (Kim //et al//., 2014).
  * Using a yeast two-hybrid screen, the pepper CaHSP70a was identified as another AvrBsT-interacting protein. Bimolecular fluorescence complementation and co-immunoprecipitation assays confirmed the specific interaction between CaHSP70a and AvrBsT //in planta//  (Kim //et al//., 2015a).
  * Using a yeast two-hybrid screen, the pepper aldehyde dehydrogenase 1 (CaALDH1) was identified as another AvrBsT-interacting protein. Bimolecular fluorescence complementation and co-immunoprecipitation assays confirmed the interaction between CaALDH1 and AvrBsT //in planta//  (Kim //et al//., 2015b).

===== Conservation =====

=== In xanthomonads ===

Yes (//X. euvesicatoria//, //X. arboricola//, //X. citri//, //X. phaseoli//, //X. vasicola//, //X. vesicatoria//).

=== In other plant pathogens/symbionts ===

Yes (//Acidovorax//  spp., //Brenneria//  spp., //Erwinia//  spp., //Pseudomonas//  spp., //Ralstonia//  spp.).

=====   =====

===== References =====

Abrahamian P, Timilsina S, Minsavage GV, Kc S, Goss EM, Jones JB, Vallad GE (2018). The type III effector AvrBsT enhances //Xanthomonas perforans//  fitness in field-grown tomato. Phytopathology 108: 1355-1362. DOI: [[https://doi.org/10.1094/PHYTO-02-18-0052-R|10.1094/PHYTO-02-18-0052-R]]

Cheong MS, Kirik A, Kim JG, Frame K, Kirik V, Mudgett MB (2014). AvrBsT acetylates //Arabidopsis//  ACIP1, a protein that associates with microtubules and is required for immunity. PLoS Pathog. 10: e1003952. DOI: [[https://doi.org/10.1371/journal.ppat.1003952|10.1371/journal.ppat.1003952]]

Ciesiolka LD, Hwin T, Gearlds JD, Minsavage GV, Saenz R, Bravo M, Handley V, Conover SM, ZhangH, Caporgno J, Phengrasamy NB, Toms AO, Stall RE, Whalen MC (1999). Regulation of expression of avirulence gene //avrRxv//  and identification of a family of host interaction factors by sequence analysis of //avrBsT//. Mol. Plant Microbe Interact. 12: 35-44. DOI: [[https://doi.org/10.1094/MPMI.1999.12.1.35|10.1094/MPMI.1999.12.1.35]]

Cunnac S, Wilson A, Nuwer J, Kirik A, Baranage G, Mudgett MB (2007). A conserved carboxylesterase is a suppressor of AvrBsT-elicited resistance in //Arabidopsis//. Plant Cell 19: 688-705. DOI: [[https://doi.org/10.1105/tpc.106.048710|10.1105/tpc.106.048710]]

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: [[https://doi.org/10.1046/j.1464-6722.2001.00077.x.|10.1046/j.1464-6722.2001.00077.x|10.1046/j.1464-6722.2001.00077.x]]

Hwang IS, Kim NH, Choi DS, Hwang BK (2012). Overexpression of //Xanthomonas campestris//  pv. //vesicatoria//  effector AvrBsTin //Arabidopsis//  triggers plant cell death, disease and defense responses. Planta 236: 1191-1204. DOI: [[https://doi.org/10.1007/s00425-012-1672-4|10.1007/s00425-012-1672-4]]

Kim NH, Choi HW, Hwang BK (2010). //Xanthomonas campestris//  pv. //vesicatoria//  effector AvrBsT induces cell death in pepper, but suppresses defense responses in tomato. Mol. Plant Microbe Interact. 23: 1069-1082. DOI: [[https://doi.org/10.1094/MPMI-23-8-1069|10.1094/MPMI-23-8-1069]]

Kim NH, Hwang BK (2015a). Pepper heat shock protein 70a interacts with the type III effector AvrBsT and triggers plant cell death and immunity. Plant Physiol. 167: 307-322. DOI: [[https://doi.org/10.1104/pp.114.253898|10.1104/pp.114.253898]]

Kim NH, Hwang BK (2015b). Pepper aldehyde dehydrogenase CaALDH1 interacts with //Xanthomonas//  effector AvrBsT and promotes effector-triggered cell death and defence responses. J. Exp. Bot. 66: 3367-3380. DOI: [[https://doi.org/10.1093/jxb/erv147|10.1093/jxb/erv147]]

Kim NH, Kim DS, Chung EH, Hwang BK (2014). Pepper suppressor of the G2 allele of //skp1//  interacts with the receptor-like cytoplasmic kinase1 and type III effector AvrBsT and promotes the hypersensitive cell death response in a phosphorylation-dependent manner. Plant Physiol. 165: 76-91. DOI: [[https://doi.org/10.1104/pp.114.238840|10.1104/pp.114.238840]]

Kim NH, Kim BS, Hwang BK (2013). Pepper arginine decarboxylase is required for polyamine and γ-aminobutyric acid signaling in cell death and defense response. Plant Physiol. 162: 2067-2083. DOI: [[https://10.1104/pp.113.217372|10.1104/pp.113.217372]]

Kirik A, Mudgett MB (2009) SOBER1 phospholipase activity suppresses phosphatidic acid accumulation and plant immunity in response to bacterial effector AvrBsT. Proc. Natl. Acad. Sci. U.S.A. 106: 20532-20537. DOI: [[https://doi.org/10.1073/pnas.0903859106|10.1073/pnas.0903859106]]

Minsavage GV, Dahlbeck D, Whalen MC, Kearny B, Bonas U, Staskawicz BJ, Stall RE (1990). Gene-for-gene relationships specifying disease resistance in //Xanthomonas campestris//  pv. //vesicatoria//-pepper interactions. Mol. Plant Microbe Interact. 3: 41-47. DOI: [[https://doi.org/10.1094/MPMI-3-041|10.1094/MPMI-3-041]]

Orth K, Xu ZH, Mudgett MB, Bao ZQ, Palmer LE, Bliska JB, Mangel WF, Staskawicz B, Dixon JE (2000). Disruption of signaling by //Yersinia//  effector YopJ, a ubiquitin-like protein protease. Science 290: 1594-1597. DOI: [[https://doi.org/10.1126/science.290.5496.1594|10.1126/science.290.5496.1594]]

Prochaska H, Thieme S, Daum S, Grau J, Schmidtke C, Hallensleben M, John P, Bacia K, Bonas U (2018). A conserved motif promotes HpaB-regulated export of type III effectors from //Xanthomonas//. Mol. Plant Pathol. 19: 2473-2487. DOI: [[https://doi.org/10.1111/mpp.12725|10.1111/mpp.12725]]

Schwartz AR, Potnis N, Timilsina S, Wilson M, Patané J, Martins J Jr, Minsavage GV, Dahlbeck D, Akhunova A, Almeida N, Vallad GE, Barak JD, White FF, Miller SA, Ritchie D, Goss E, Bart RS, Setubal JC, Jones JB, Staskawicz BJ (2015). Phylogenomics of //Xanthomonas//  field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity. Front. Microbiol. 6: 535. DOI: [[https://doi.org/10.3389/fmicb.2015.00535|10.3389/fmicb.2015.00535]]

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: [[https://doi.org/10.1111/j.1469-8137.2010.03346.x|10.1111/j.1469-8137.2010.03346.x]]

===== Further reading =====

Han SW, Hwang BK (2017). Molecular functions of //Xanthomonas//  type III effector AvrBsT and its plant interactors in cell death and defense signaling. Planta 245: 237-253. DOI: [[https://doi.org/10.1007/s00425-016-2628-x|10.1007/s00425-016-2628-x]]

Timilsina S, Abrahamian P, Potnis N, Minsavage GV, White FF, Staskawicz BJ, Jones JB, Vallad GE, Goss EM (2016). Analysis of sequenced genomes of Xanthomonas perforans identifies candidate targets for resistance breeding in tomato. Phytopathology 106: 1097-1104. DOI: [[https://doi.org/10.1094/PHYTO-03-16-0119-FI|10.1094/PHYTO-03-16-0119-FI]]