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

Author: [[https://www.researchgate.net/profile/Guido_Sessa|Guido Sessa]]\\
Internal reviewer: [[https://www.researchgate.net/profile/David_Studholme|David J. Studholme]]\\
Expert reviewer: [[https://www.researchgate.net/profile/Laurent_Noel|Laurent Noël]]

Class: XopAE\\
Family: XopAE\\
Prototype: HpaF/HpaG (//Xanthomonas euvesicatoria// pv. //euvesicatoria//, ex //Xanthomonas campestris// pv. //vesicatoria//; strain 85-10)\\
GenBank ID: [[https://www.ncbi.nlm.nih.gov/protein/AAL78290.1|AAL78290.1]] (197 aa) / [[https://www.ncbi.nlm.nih.gov/protein/AAL78291.1|AAL78291.1]] (432 aa)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_011050288.1|WP_011050288.1]] (547 aa)\\
Synonyms: XopAE was also referred to as HpaF (Kim //et al.//, 2003; Sugio //et al.//, 2005). In //Xcv// strain 85-10, the gene is bipartite and the two parts were first coined //hpaF// and //hpaG// (Noël //et al.//, 2002). Be careful: //hpaG// was also used in other Xanthomonas to designate the homolog of //hpa1// (//X. campestris//, //X. oryzae//) and //xopA// (//Xcv// 85-10) (Kim //et al.//, 2003).\\
3D structure: Most XopAE pocesses a N-terminal leucine-rich repeat (LRR) domain and a C-terminal XL box motif with an E3 ubiquitin ligase fold, based on homology modelling (Popov //et al//., 2018). Predicted fold of XopAE C terminus is similar to that of XopL (Popov //et al//., 2018).
===== The locus =====

The //xopAE// locus in the majority of the //Xanthomonas// strains encodes a single ORF (//xopAE//). Yet, in //X. euvesicatoria// strain 85-10, a frame-shift splits it into two ORFs (//hpaF// and //xopAE<sub>85-10</sub> //) that are transcribed in an operon as a bicistronic mRNA (Noël //et al//., 2002; Popov //et al//., 2018).
===== Biological function =====

=== How discovered? ===

XopAE was discovered by studying //hrpG//-regulated genes within the //hrp// gene cluster of //X. euvesicatoria// strain 85-10 (Noël //et al//., 2002).
=== (Experimental) evidence for being a T3E ===

XopAE<sub>85-10</sub> was fused to the AvrBs2 reporter and shown to translocate into plant cells in an //hrpF//-dependent manner (Popov //et al//., 2018).
=== Regulation ===

In //X. euvesicatoria// strain 85-10, //xopAE// <sub>85-10</sub> transcription is driven by the promoter of the immediately upstream //hpaF// gene and regulated by the HrpX and HrpG master transcriptional regulators of the //Xanthomonas// T3SS (Popov //et al//., 2016). An imperfect PIP box (TTCGC-N<sub>16</sub>-TTCGC) is located 82 bp upstream of the predicted translation start codon of //hpaF// (Noël //et al//., 2002).
=== Phenotypes ===

XopAE<sub>85-10</sub> is a suppressor of PTI that was shown to inhibit flg22-mediated signaling in //Arabidopsis// and tomato protoplasts, downstream or in parallel to the activation of the MPK3 and MPK6 MAP kinases. //Pseudomonas syringae//-mediated delivery of XopAE<sub>85-10</sub> in plants inhibits PTI-associated callose deposition at the cell wall and enhances disease symptoms in tomato (Popov //et al//., 2016).
=== Localization ===

XopAE<sub>85-10</sub>-YFP fusion protein localizes to the cytoplasm and nucleus of //Nicotiana benthamiana// leaf epidermal cells (Popov //et al//., 2016).
=== Enzymatic function ===

XopAE<sub>85-10</sub> is an active E3 ubiquitin ligase //in vitro// (Popov //et al//., 2018).
=== Interaction partners ===

Unknown.

===== Conservation =====

=== In xanthomonads ===

Yes (Popov //et al//., 2018). The //xopAE// locus is present in sequenced genomes of //X. alfalfae//, //X. euvesicatoria//, //X. oryzae//, //X. bromi//, //X. vasicola// and //X. fragariae//, but not in //X. campestris// pv. //campestris//, for instance.
=== In other plant pathogens/symbionts ===

Yes. There are homologues in //Acidovorax// spp. (sharing up to about 50% amino-acid sequence identity) and in //Ralstonia //spp//.// (less than 35% sequence identity).
===== References =====

Kim JG, Park BK, Yoo CH, Jeon E, Oh J, Hwang I (2003). Characterization of the //Xanthomonas axonopodis// pv. //glycines// Hrp pathogenicity island. J. Bacteriol. 185: 3155‐3166. DOI: [[https://doi.org/10.1128/jb.185.10.3155-3166.2003|jb.185.10.3155-3166.2003]]

Noël L, Thieme F, Nennstiel D, Bonas U (2002). Two novel type III-secreted proteins of //Xanthomonas// //campestris// pv. //vesicatoria// are encoded within the hrp pathogenicity island. J. Bacteriol. 184: 1340-1348. DOI: [[https://doi.org/10.1128/JB.184.5.1340-1348.2002|10.1128/JB.184.5.1340-1348.2002]]

Popov G, Fraiture M, Brunner F, Sessa G (2016). Multiple //Xanthomonas// //euvesicatoria// type III effectors inhibit flg22-triggered immunity. Mol. Plant Microbe Interact. 29: 651-660. DOI: [[https://doi.org/10.1094/MPMI-07-16-0137-R|10.1094/MPMI-07-16-0137-R]]

Popov G, Majhi BB, Sessa G (2018). Effector gene //xopAE// of //Xanthomonas euvesicatoria// 85-10 is part of an operon and encodes an E3 ubiquitin ligase. J. Bacteriol. 16: e00104-18. DOI: [[https://doi.org/10.1128/JB.00104-18|10.1128/JB.00104-18]]

Sugio A, Yang B, White FF (2005). Characterization of the //hrpF// pathogenicity peninsula of //Xanthomonas oryzae// pv. //oryzae//. Mol. Plant Microbe Interact. 18: 546‐554. DOI: [[https://doi.org/10.1094/MPMI-18-0546|10.1094/MPMI-18-0546]]

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

Zhao S, Mo WL, Wu F, Tang W, Tang JL, Szurek B, Verdier V, Koebnik R, Feng JX (2013). Identification of non-TAL effectors in //Xanthomonas oryzae// pv. //oryzae// Chinese strain 13751 and analysis of their role in the bacterial virulence. World J. Microbiol. Biotechnol. 29: 733-744. DOI: [[https://doi.org/10.1007/s11274-012-1229-5|10.1007/s11274-012-1229-5]]

===== Acknowledgements =====

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