====== The Type III Effector XopZ from //Xanthomonas// ======
Author: Marlène Lachaux\\
Internal reviewer: [[https://www.researchgate.net/profile/Joel_Pothier2|Joël F. Pothier]]\\
Expert reviewer: **WANTED!**
Class: XopZ\\
Family: XopZ1, XopZ2\\
Prototype: XOO2402 (//Xanthomonas oryzae// pv. o//ryzae//; strain T7174)\\
GenBank ID (XopZ1): [[https://www.ncbi.nlm.nih.gov/protein/BAE69157.1|BAE69157.1]] (1288 aa)\\
GenBank ID (XopZ2): [[https://www.ncbi.nlm.nih.gov/protein/EGD08510.1|EGD08510.1]] (1265 aa)\\
RefSeq ID (XopZ1): [[https://www.ncbi.nlm.nih.gov/protein/WP_011259177.1|WP_011259177.1]] (1388 aa)\\
RefSeq ID (XopZ2): [[https://www.ncbi.nlm.nih.gov/protein/WP_039421390.1|WP_039421390.1]] (1317 aa)\\
Examples of other XopZ1 sequences: [[https://www.ncbi.nlm.nih.gov/protein/ACD59124.1|ACD59124.1]] and [[https://www.ncbi.nlm.nih.gov/protein/ACD59315.1|ACD59315.1]] (=PXO_01041 and PXO_06152, respectively, as strain PXO99A contains two identical copies of the gene due to a 212-kb duplication in the genome) (Song //et al.//, 2010). These GenBank entries are only 1371 aa long whereas the first functional characterization proposes 1414 aa, thus positioning the PIP box (TTCTC-N15-TTCGC) 58 bp upstream of the predicted translation start site (Song and Yang, 2010). [[https://www.ncbi.nlm.nih.gov/protein/AAW75797.1|AAW75797.1]] (1414 aa) in strain KACC 10331 might be preferred.\\
Examples of other XopZ2 sequences: [[https://www.ncbi.nlm.nih.gov/protein/EGD18683.1|EGD18683.1]] (1318 aa)\\
3D structure: Unknown. The N-terminus of XopZPXO99, contains two Nuclear Localization Signals (NLS) and several Nuclear Export Signals (NES) (Zhou //et al.//, 2015).
===== Biological function =====
=== How discovered? ===
The first mention of XopZ as an homolog of HopAS1 in// Xanthomonas oryzae// MAFF311018 was made by Furutani //et al.// (2009). Indeed, the locustag XOO2402 ([[https://www.ncbi.nlm.nih.gov/protein/BAE69157.1|BAE69157.1]]; 1,288 aa) was shown to share homology with known Hrp outer proteins (Hops) of //Pseudomonas syringae// strains (Lindeberg //et al.//, 2005).
In 2009, the generation of mutants for 18 non-TAL type 3 effector genes in //Xoo// strain PXO99A allowed to investigate the function of several T3Es. Among them XopZ (PXO_06152 and PXO_01041) was reported to contribute to the full virulence of the strain PXO99A (Ryan //et al.//, 2009; Song and Yang, 2010).
XopZ2 was described in Potnis //et al.//, 2011 as a novel candidate effector gene upstream of //hrpW// in //Xanthomonas vesicatoria// strain 1111 (=ATCC 35937) ([[https://www.ncbi.nlm.nih.gov/protein/EGD08510.1|EGD08510.1]]=XVE_3221) and //Xanthomonas gardneri// strain 101 (=ATCC 19865) ([[https://www.ncbi.nlm.nih.gov/protein/EGD18683.1|EGD18683.1]]=XGA_2762; Potnis //et al.//, 2011). It was also shown to be functional i.e. as being translocated using a reporter gene assay (AvrBs2-based assay; Potnis //et al.//, 2011). The pairwise sequence identity below 50% warrants assigning these two proteins to a new family within the XopZ class, named XopZ2 (Potnis //et al.//, 2011).
=== (Experimental) evidence for being a T3E ===
The secretion of XopZ //in planta// was shown using a //B. pertussis// Cya translocation reporter assay (Furutani //et al.//, 2009). With a PIP box 58 bp 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 (Song and Yang, 2010). PXO99A and an //hrpG// mutant were grown in nutrient broth (NB) or //Xanthomonas hrp//-inducing medium (XOM2) (Song and Yang, 2010). The expression of //xopZ// PXO99 was only observed, by RT-PCR, in XOM2 medium and was //hrpG// dependent (Song and Yang, 2010).
=== Regulation ===
The //xopZ// gene was shown to be expressed in a //hrpG//-dependent manner. A PIP box (TTCTC-N15-TTCGC) was identified 58 bp upstream of the predicted translation start site (Song and Yang, 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// Δ//xrvC// mutant compared with those in the wild-type strain PXO99A (Liu //et al.//, 2016).
=== Phenotypes ===
PXO99A 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 PXO99A . The introduction of one genomic copy of //xopZ// PXO99 restores the mutant to full virulence. To test whether XopZPXO99 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 PXO99A (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 XopZPXO99 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 PXO99A in rice protoplasts results in compromised OsMAPK activation induced by PGN, highlighting their putative virulence functions during pathogenesis (Long //et al.//, 2018).
A role of XopZ in full virulence was also clearly shown in //Xanthomonas axonopodis// pv. //manihotis// CIO151 but not in PTI or ETI supression, at least under the tested conditions, as on the contrary to XopZ of //X. oryzae// pv. //oryzae// PXO99, no reduction of callose deposition was observed (Medina //et al.//, 2017).
=== Localization ===
XopZPXO99 localizes in the cytoplasm and nucleus of the plant cell (Zhou //et al.//, 2015).
=== Enzymatic function ===
XopZPXO99 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).
=== Interaction partners ===
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).
===== Conservation =====
=== In xanthomonads ===
Yes, found to be conserved in all //Xanthomonas//spp. (whose genomes have been sequenced) with the exception of some clade-1 strains (//e.g.// //X. albilineans//) (Song and Yang, 2010; Sinha //et al.//, 2013).
=== In other plant pathogens/symbionts ===
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 and Yang, 2010).
===== References =====
Furutani A, Takaoka M, Sanada H, Noguchi Y, Oku T, Tsuno K, Ochiai H, Tsuge S (2009). Identification of novel type III secretion effectors in //Xanthomonas oryzae// pv. //oryzae//. Mol. Plant Microbe Interact. 22: 96-106. DOI: [[https://doi.org/10.1094/MPMI-22-1-0096|10.1094/MPMI-22-1-0096]]
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: [[https://doi.org/10.1093/femsle/fnw067|10.1093/femsle/fnw067]]
Lindeberg M, Stavrinides J, Chang JH, Alfano JR, Collmer A, Dangl JL, Greenberg JT, Mansfield JW, Guttman DS (2005). Proposed guidelines for a unified nomenclature and phylogenetic analysis of type III Hop effector proteins in the plant pathogen //Pseudomonas syringae//. Mol Plant Microbe Interact. 18: 275-282. DOI: [[https://doi.org/10.1094/mpmi-18-0275|10.1094/MPMI-18-0275]]
Long J, Song C, Yan F, Zhou J, 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: [[https://doi.org/10.3389/fpls.2018.01857|10.3389/fpls.2018.01857]]
Medina CA, Reyes PA, Trujillo CA, Gonzalez JL, Bejarano DA, Montenegro NA, Jacobs JM, Joe A, Restrepo S, Alfano JR, Bernal A (2018). The role of type III effectors from //Xanthomonas axonopodis// pv. //manihotis// in virulence and suppression of plant immunity. Mol. Plant Pathol. 19: 593-606. DOI: [[https://doi.org/10.1111/mpp.12545|10.1111/mpp.12545]]
Potnis N, Krasileva K, Chow V, Almeida NF, Patil PB, Ryan RP, Sharlach M, Behlau F, Dow JM, Momol M, White FF, Preston JF, Vinatzer BA, Koebnik R, Setubal JC, Norman DJ, Staskawicz BJ, Jones JB (2011). Comparative genomics reveals diversity among xanthomonads infecting tomato and pepper. BMC Genomics 12: 146. DOI: [[https://doi.org/10.1186/1471-2164-12-146|10.1186/1471-2164-12-146]]
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: [[https://doi.org/10.1111/j.1462-5822.2009.01387.x|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: [[https://doi.org/10.1371/journal.pone.0075867|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: [[https://doi.org/10.1094/MPMI-23-7-0893|10.1094/MPMI-23-7-0893]]
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: [[https://lib.dr.iastate.edu/etd/14469/|lib.dr.iastate.edu/etd/14469/]]
===== Acknowledgements =====
This fact sheet is based upon work from COST Action CA16107 EuroXanth, supported by COST (European Cooperation in Science and Technology).