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Molecular Diagnosis and Diversity for Regulated Xanthomonas
Bacterial virulence factors
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Author: Guido Sessa
Internal reviewer: David J. Studholme
Expert reviewer: 
Class: XopAE
Family: XopAE
Prototype: XopAE (Xanthomonas euvesicatoria pv. euvesicatoria, ex Xanthomonas campestris pv. vesicatoria; strain 85-10)
RefSeq ID: WP_011050288.1 (547 aa)
Synonyms: XopAE 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 coined hpaF and hpaG (Noël et al., 2002). However, hpaG was used by others to designate the homolog of hpa1 (X. campestris, X. oryzae) and xopA (Xcv 85-10) (Kim et al., 2003).
3D structure: E3 ubiquitin ligase, based on homology modelling. Similar fold to that of XopL (Popov et al., 2018).
The xopAE locus in the majority of the Xanthomonas strains encodes a single ORF (xopAE), while in X. euvesicatoria strain 85-10 a frame-shift splits it into two ORFs (hpaF and xopAE85-10 ) that are transcribed in an operon as a bicistronic mRNA (Noël et al., 2002).
XopAE was discovered by DNA sequencing of the X. euvesicatoria strain 85-10 hrp cluster (Noël et al., 2002).
XopAE preceded by hpaF was fused to the AvrBs2 reporter and shown to translocate into plant cells in an hrpF-dependent manner (Popov et al., 2018).
In X. euvesicatoria strain 85-10, xopAE 85-10 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-N16-TTCGC) is located 82 bp upstream of the predicted translation start codon of hpaF (Noël et al., 2002).
XopAE85-10 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. Expression of XopAE85-10 in plants inhibits PTI-associated callose deposition at the cell wall and enhances disease symptoms (Popov et al., 2016).
Cytoplasm and nucleus (Popov et al., 2016).
XopAE is an active E3 ubiquitin ligase in vitro (Popov et al., 2018).
Unknown.
Yes (e.g., the xopAE locus is present in sequenced genomes of X. alfalfae, X. euvesicatoria, X. oryzae, X. bromi, X. vasicola and X. fragariae).
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).
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: 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: 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: 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: 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: 10.1094/MPMI-18-0546
