Author: Marlène Lachaux
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Class: XopZ
Family: XopZ
Prototype: XopZ (Xanthomonas oryzae pv. oryzae, PXO99^A )
RefSeq ID: 1,414-amino-acid protein 3D structure: The N-terminus of XopZ_PXO99, containing two Nuclear Localization Signals (NLS) signals and several Nuclear Export Signals (NES) (Zhou et al., 2015).

In 2009, generation of PXO99 mutants for 18 non-TAL T3 effector genes allowed to investigate the function of several T3Es in Xoo strain PXO99^A . It was reported on XopZ that contributes to the full virulence of the strain PXO99^A (Ryan et al., 2009; Song et al., 2010).

With a PIP box upstream of the predicted translation start site XopZ_PXO99 gene is certainly inducible in planta and regulated through the hypersensitive reaction and pathogenicity (hrp) regulatory network. PXO99^A and an hrpG mutant were grown in NB or Xanthomonas hrp-inducing medium (XOM2). The expression of XopZ_PXO99 was only observed, by (RT)-PCR, in XOM2 medium and was hrpG dependent (Song et al., 2010).

The XopZ gene was shown to be expressed in a hrpG-dependent manner. Presence of a PIP box (TTCTC-N15-TTCGC) 58 bp upstream of the predicted translation start site (Song et al., 2010).

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 xopZ, 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).

PXO99^A contains two identical copies of the gene due to a duplication of 212 kb in the genome. However, a deletion of one XopZ gene did not affect pathogenicity or bacterial growth in plants, while strains with mutations in both copies of XopZ_PXO99 displayed reduced virulence in terms of lesion length and bacterial multiplication compared with the wild type strain PXO99^A . The introduction of one genomic copy of XopZ_PXO99 restores the mutant to full virulence. To test whether XopZ_PXO99 inhibits the host cell-wall-associated defense responses (PTI), leaves of Nicotiana benthamiana were infiltrated with Agrobacterium cells with and without XopZ_PXO99 under the control of the Cauliflower mosaic virus 35S promoter 24 hours preceding inoculation of the same leaves with a T3SS mutant of PXO99^A (ME7). Twenty-four hours after inoculation, leaves inoculated with ME7 had more callose depositions than the leaves inoculated with Agrobacterium spp. expressing XopZ_PXO99 . This results suggesting a role for XopZ_PXO99 in interfering with host innate immunity (PTI) during X. oryzae pv. oryzae infection (Song et al., 2010). Besides, Western blot analysis with p44/42 MAP kinase antibody clearly showed that XopN, XopV and XopZ inhibited the peptidoglycan(PNG)-induced phosphorylation of OsMAPKs. Expression of all Xop effectors were verified by immunoblotting with anti-HA antibody. Thus, expression of three Xop effectors from PXO99^A in rice protoplasts results in compromised OsMAPK activation induced by PGN, highlighting their putative virulence functions during pathogenesis (Zhou et al., 2018).

XopZ_PXO99 localizes in the cytoplasm and nucleus of the plant cell (Zhou et al., 2015).

XopZ_PXO99 functions as a suppressor of LipA-induced innate immune responses since the mutation of XopZ partially compromises virulence while quadruple mutant of XopN/XopQ/XopX/XopZ induces calloses deposition just similarly to Xoo T3SS-mutant in rice leaves (Sinha et al., 2013). The function of XopZ is also to stabilize a putative host E3 ubiquitin ligase protein PBP (s-ribonuclease) in the nucleus and prevents its degradation-mediated by a cysteine protease (C1A) in plant cells. XopZ may function to interfere with the homeostatic state of the negative regulator (PBP) in immune system in rice, and subvert the plant immune response (Zhou et al., 2015).

XopZ interacts with a putative host E3 ubiquitin ligase protein PBP (s-ribonuclease) in vitro and in vivo. Regions containing 193 aa - 225 aa of PBP is required for interacting with XopZ. PBP is a negative regulator of host immune response based on the disease phenotype in PBP-knockout rice plants. C1A directly interacts and strongly degrades PBP through its cysteine protease activity, leading to a homeostatic state of PBP in plant cells (Zhou et al., 2015).

Yes, is found to be conserved in all Xanthomonas spp. (whose genomes have been sequenced) with the exception of X. albilineans strain (Song et al., 2010; Sinha et al., 2013).

Related genes are also found in several Pseudomonas syringae pathovars (HopAs1 relatives), a few strains of Ralstonia solanacearum (AWR proteins), and the AAC00-1 strain of Acidovorax avenae subsp. citrulli (Song et al., 2010).

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

Ryan RP, Koebnik R, Szurek B, Boureau T, Bernal A, Bogdanove A, Dow JM (2009). Passing GO (gene ontology) in plant pathogen biology: a report from the Xanthomonas Genomics Conference. Cell. Microbiol. 11: 1689-1696. DOI: 10.1111/j.1462-5822.2009.01387.x

Sinha D, Gupta MK, Patel HK, Ranjan A, Sonti RV (2013). Cell wall degrading enzyme induced rice innate immune responses are suppressed by the type 3 secretion system effectors XopN, XopQ, XopX and XopZ of Xanthomonas oryzae pv. oryzae. PLoS One 8: e75867. DOI: 10.1371/journal.pone.0075867

Song C, Yang B (2010). Mutagenesis of 18 type III effectors reveals virulence function of XopZ _PXO99 in Xanthomonas oryzae pv. oryzae. Mol. Plant Microbe Interact. 23: 893-902. DOI: 10.1094/MPMI-23-7-0893

Zhou H, Yang B (2018). Non-TAL effectors from Xanthomonas oryzae pv. oryzae suppress peptidoglycan-triggered MAPK activation in rice. Front. Plant Sci. 9: 1857. DOI: 10.3389/fpls.2018.01857

Zhou J (2015). Host target genes of the Xanthomonas oryzae pv. oryzae type III effectors for bacterial blight in rice. Doctoral Thesis, Iowa State University, USA. PDF: lib.dr.iastate.edu/etd/14469/