Author: David J. Studholme
Internal reviewer: Laurent D. Noël
Expert reviewer: WANTED!

Class: XopAD
Family: XopAD
Prototypes: XAC4213 (Xanthomonas citri pv. citri; strain 306), XOO4145 (Xanthomonas oryzae pv. oryzae; strain T7174)
GenBank ID (XAC4213): AAM39048.1 (2883 aa)
GenBank ID (XOO4145): BAE70900.1 (2927 aa)
RefSeq ID: WP_011409710.1 (2927 aa)
3D structure: Unknown

XopAD was first described as a homologue of a type 3 effector from Ralstonia solanacearum (BAH47290.1) (White et al., 2009) and later re-discovered using a machine-learning approach (Teper et al., 2016).

XopAD fused to the AvrBs2 reporter domain, was shown to translocate into plant cells in an hrpF-dependent manner.

No PIP box was found in the promoter region of xopAD in X. euvesicatoria pv. euvesicatoria strain 85-10 (Teper et al., 2016).

qRT-PCR revealed that transcript levels of 15 out of 18 tested non-TAL effector genes (as well as the regulatory genes hrpG and hrpX), including xopAD, were significantly reduced in the Xanthomonas oryzae pv. oryzae ΔxrvC mutant compared with those in the wild-type strain PXO99^A (Liu et al., 2016).

Deletion of xopAD does not alter X. citri pv. citri pathogenicity (Escalon et al., 2013).

Unknown.

Not known. However, the 614 amino acid protein consists of multiple armadillo repeats of semi-conserved 42 amino acids. The C-terminal domain, which is absent in Xcv 85-10 XopAD but present in the ~2880 amino acid homologues (see below), encodes a putative RelA-like nucleotidyltransferase domain (Teper et al., 2016).

Not known.

Yes. XopAD has homologues encoded in the genomes of most Xanthomonas species (Teper et al., 2016), including X. axonopodis (Harrison & Studholme, 2014), X. vasicola (Studholme et al., 2010; Wasukira et al., 2012), X. nasturtii (Vicente et al., 2010), X. citri (Escalon et al., 2013). In this respect, Xanthomonas campestris appears to be an exception. Escalon and colleagues state: “The analysis of xopAD and xopAG suggested horizontal transfer between X. citri pv. bilvae, another citrus pathogen, and some X. citri pv. citri strains” (Escalon et al., 2013). The prototype sequence from X. euvesicatoria pv. euvesictoria strain 85-10 (Teper et al., 2016) is 614 amino acids in length and marked in GenBank as a fragment. Homologues in other genomes of this species range from 2840 aa (RefSeq: WP_046939801.1) to 2885 aa (RefSeq: WP_033837371.1) in length and the authors of the prototype study state: “We hypothesize that the ORFs annotated as XCV1197 (XopAV) and XCV1198, and XCV4315 (XopAD), XCV4314 and XCV4313, were originally two complete ORFs that were later truncated by the introduction of early stop codons” (Teper et al., 2016). Therefore, the full-length homologues found in other genomes might not be functionally equivalent to the prototype XopAD. The introduction of early stop codons is explained by presence of an ISXac5-related insertion sequence (Escalon et al., 2013).

Yes. XopAD is homologous to members of the RipS1 family of effectors in Ralstonia solanacearum (Peeters et al., 2013).

Escalon A, Javegny S, Vernière C, Noël LD, Vital K, Poussier S, Hajri A, Boureau T, Pruvost O, Arlat M, Gagnevin L (2013). Variations in type III effector repertoires, pathological phenotypes and host range of Xanthomonas citri pv. citri pathotypes. Mol. Plant Pathol. 14: 483-496. DOI: 10.1111/mpp.12019

Harrison J, Studholme DJ (2014). Draft genome sequence of Xanthomonas axonopodis pathovar vasculorum NCPPB 900. FEMS Microbiol. Lett. 360: 113-116. DOI: 10.1111/1574-6968.12607

Liu Y, Long J, Shen D, Song C (2016). Xanthomonas oryzae pv. oryzae requires H-NS-family protein XrvC to regulate virulence during rice infection. FEMS Microbiol. Lett. 363: fnw067. DOI: 10.1093/femsle/fnw067

Peeters N, Carrère S, Anisimova M, Plener L, Cazalé AC, Genin S (2013). Repertoire, unified nomenclature and evolution of the type III effector gene set in the Ralstonia solanacearum species complex. BMC Genomics 14: 859. DOI: 10.1186/1471-2164-14-859

Studholme DJ, Kemen E, MacLean D, Schornack S, Aritua V, Thwaites R, Grant M, Smith J, Jones JD (2010). Genome-wide sequencing data reveals virulence factors implicated in banana Xanthomonas wilt. FEMS Microbiol. Lett. 310: 182-192. DOI: 10.1111/j.1574-6968.2010.02065.x

Teper D, Burstein D, Salomon D, Gershovitz M, Pupko T, Sessa G (2016). Identification of novel Xanthomonas euvesicatoria type III effector proteins by a machine-learning approach. Mol. Plant Pathol. 17: 398-411. DOI: 10.1111/mpp.12288

Vicente JG, Rothwell S, Holub EB, Studholme DJ (2017). Pathogenic, phenotypic and molecular characterisation of Xanthomonas nasturtii sp. nov. and Xanthomonas floridensis sp. nov., new species of Xanthomonas associated with watercress production in Florida. Int. J. Syst. Evol. Microbiol. 67: 3645-3654. DOI: 10.1099/ijsem.0.002189

Wasukira A, Tayebwa J, Thwaites R, Paszkiewicz K, Aritua V, Kubiriba J, Smith J, Grant M, Studholme DJ (2012). Genome-wide sequencing reveals two major sub-lineages in the genetically monomorphic pathogen Xanthomonas campestris pathovar musacearum. Genes (Basel) 3: 361-377. DOI: 10.3390/genes3030361

White FF, Potnis N, Jones JB, Koebnik R (2009). The type III effectors of Xanthomonas. Mol. Plant Pathol. 10: 749-66. DOI: 10.1111/j.1364-3703.2009.00590.x

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