Author: Saul Burdman
Internal reviewer:
Expert reviewer:

Class: XopAP
Family: XopAP
Prototype: XopAP (Xanthomonas euvesicatoria pv. euvesicatoria aka Xanthomonas campestris pv. vescicatoria; strain 85-10)
RefSeq ID: CAJ24869.1 (464 aa)
3D structure: Unknown

XopAP (XCV3138 in X. euvesicatoria 85-10; GenBank AM039952.1) was discovered using a machine-learning approach (Teper et al., 2016).

XopAP fused to the AvrBs2 reporter, was shown to translocate into plant cells in an hrpF-dependent manner (Teper et al., 2016).

Unknown. In X. euvesicatoria 85-10, the xopAP gene does not contain a PIP-box motif in its promoter region (Teper et al., 2016).

A Xanthomonas euvesicatoria 85-10 mutant defective in xopAP was compromised in induction of disease symptoms in leaves of susceptible pepper plants, relative to wild-type 85-10. This phenotype was associated with reduced ion leakage and higher chlorophyll content as compared with leaves inoculated with wild-type 85-10. No differences were observed between the xopAP mutant and wild-type 85-10 in their ability to colonize the leaves of susceptible pepper plants(Teper et al., 2016). Agrobacterium-mediated expression of XopAP in Nicotiana benthamiana caused a bleaching phenotype that was detected 3 days after agroinfiltration, and was reflected by reduced chlorophyll content. However, in these experiments, XopAP did not induce significant increase in ion leakage in the inoculated area (Teper et al., 2016). Results from this study indicate that XopAP acts as a virulence determinant in X. euvesicatoria, and contributes to the development of disease symptoms. A further study by Popov and colleagues revealed that XopAP was among the X. euvesicatoria 85-10 effectors that inhibited PAMP-triggered immunity, as assessed by inhibition of activation of a flg22-inducible reporter gene in Arabidopsis protoplasts (Popov et al., 2018). Expression of XopAP in an attenuated mutant of Pseudomonas syringae pv. tomato (DC3000 ΔCEL) increased its virulence on tomato. Also, the DC3000 ΔCEL strain carrying xopAP induced decreased callose deposition in Arabidopsis cell walls than the DC3000 ΔCEL strain (Popov et al., 2018). XopAP shares similarity with the Ralstonia solanacearum type III effector RipAL and both effectors possess a putative lipase domain (Peeters et al., 2013; Teper et al., 2016). R. solanacearum RipAL was shown to suppress salicylic acid-mediated defense responses and induce jasmonic acid production in N. benthamiana (Nakano & Mukaihara, 2018). Mutations in the putative catalytic residues within the lipase-like domain of RipAL abolished these activities (Nakano & Mukaihara, 2018).

Unknown. Subcellular localization analyses of the R. solanacearum homolog, RipAL, suggested that RipAL localizes to chloroplasts and targets chloroplast lipids in plant cells (Nakano & Mukaihara, 2018).

Unknown. XopAL contains a putative lipase domain (lipase class 3 family domain; conserved protein domain family PLN03037) in amino acid positions 236-322 (Teper et al., 2016).

Unknown.

Yes (e.g., X. campestris, X. axonopodis, X. perforans, X. citri, X. alfalfae, X. prunicola, X. phaseoli, X. hortorum, X. arboricola, X. translucens, X. oryzae, X. hyacinthi)

Yes (Ralstonia solanacearum, plant-pathogenic Acidovorax species, Brenneria rubrifaciens, Robbsia andropogonis)

Nakano M, Mukaihara T (2018). Ralstonia solanacearum type III effector RipAL targets chloroplasts and induces jasmonic acid production to suppress salicylic acid-mediated responses in plants. Plant Cell Physiol. 59(12):2576-2589. DOI: 10.1093/pcp/pcy177.

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

Popov G, Fraiture M, Brunner F, Sessa G (2018). Multiple Xanthomonas euvesicatoria type III effectors inhibit flg22-triggered immunity. Mol. Plant-Microbe Interact. 29(8):651-660. DOI: 10.1094/MPMI-07-16-0137-R

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(3): 398-411. DOI: 10.1111/mpp.12288