====== XopL ======

Author: [[https://www.researchgate.net/profile/Joana_Vicente2|Joana G. Vicente]]\\
Internal reviewer: [[https://www.researchgate.net/profile/Joel_Pothier2|Joël F. Pothier]]\\
Expert reviewer: FIXME

Class: XopL\\
Family: XopL\\
Prototype: XCV3220 (//Xanthomonas euvesicatoria// pv. //euvesicatoria//, ex //Xanthomonas campestris// pv. //vesicatoria//; strain 85-10)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/CAJ24951|CAJ24951]] (660 aa)\\
Examples of other sequences: XopL<sub>Xcv85-10</sub> [[https://www.ncbi.nlm.nih.gov/protein/CAJ24951.1|CAJ24951.1]] (X. //euvesicatoria// pv. //euvesicatoria//); XopK<sub>Xcc306</sub> [[https://www.ncbi.nlm.nih.gov/protein/21109412|21109412]] (//X. citri// pv. //citri//); XopL<sub>Xcc8004</sub> [[https://www.ncbi.nlm.nih.gov/protein/66575899|66575899]] (//X. campestris// pv. //campestris//)\\
3D structure: [[https://www.rcsb.org/structure/4FC9|4FC9]], [[https://www.rcsb.org/structure/4FCG|4FCG]] (Singer //et al//., 2013). Full-length XopL<sub>Xcv85-10</sub> did not crystallize but fragments XopL[aa 144–450] and XopL[aa 474–660] yielded crystals (Singer //et al//., 2013). The crystal structure of the N-terminal region of XopL showed the presence of a leucine-rich repeat (LRR) domain, that might serve as a protein-protein interaction module for ubiquitination target recognition (Singer //et al//., 2013). The protein represents a new class of E3 ubiquitin ligases.

===== Biological function =====

=== How discovered? ===

XopL was first identified in //X. campestris// pv. //campestris// (//Xcc//) strain 8004 as a candidate T3E due to the presence of a plant-inducible promoter (PIP) box in its gene, XC_4273 (Jiang //et al.//, 2009). The CDS //XC_4273//, re-called XopXccLR (LR = leucine-rich repeat), in //X//. //campestris// pv. //campestris// 8004 was suggested to be a T3E has it harboured a N-terminal region possessing translocation signal with the functionality to target proteins into plant cells (Jiang //et al//., 2009). It was also shown to be required for //X//. //campestris// pv. //campestris// to proliferate well in hosts plant and thus essential for virulence (Jiang //et al//., 2009). It's only a few years later that the analysis of the genome sequence of //Xcv// strain 85-10 led to the identification of XCV3220 (//xopL//) as a new T3E candidate gene and to its more complete characterization (Singer //et al//., 2013).
=== (Experimental) evidence for being a T3E ===

Using an AvrBs1 reporter fusion, XopL<sub>Xcc8004</sub> was shown to be translated into plant cells in a //hrpF//- and //hpaB//-dependent manner (Jiang et al., 2009).

XopL<sub>Xcv85-10</sub> contains a PIP box (plant inducible promoter) in its promoter (TTCG-N<sub>16</sub>-TTCG; genome position 3669238-261); co-regulation with the T3S system was confirmed by RT-PCR (Singer //et al//., 2013). Contains leucine-rich repeats (LRRs). Type III-dependent secretion and translocation was confirmed by //in vitro// secretion and //in vivo// translocation assays (Singer //et al//., 2013). Mutation of amino acids in the central cavity of the XL-box disrupts E3 ligase activity and prevents XopL-induced plant cell death. The lack of cysteine residues in the XL-box suggests the absence of thioester-linked ubiquitin-E3 ligase intermediates and a non-catalytic mechanism for XopL-mediated ubiquitination. The E3 ligase activity is required to provoke plant cell death, suppression of PAMP responses solely depends on the N-terminal LRR domain (Singer //et al//., 2013). XopL<sub>Xcc8004</sub> possesses features that are typical of T3Es: the promoter region of xopL<sub>Xcc8004</sub> gene contains a perfect plant inducible promoter (PIP) box followed by a 10 box similar sequence (TTCGC-N<sub>15</sub>-TTCGC-N<sub>31</sub>-ACGACA) and LRRs motif is characteristic of specific T3Es in pathogenic bacteria (Yan //et al//., 2019).
=== Regulation ===

The //xopL// <sub>Xcc8004</sub> gene contains a PIP box and was shown to be controlled by //hrpG// and //hrpX// (Jiang et al., 2009).

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 //xopL//, were significantly reduced in the //Xanthomonas oryzae// pv. //oryzae// Δ//xrvC// mutant compared with those in the wild-type strain PXO99<sup>A</sup>  (Liu //et al.//, 2016).

The expression of //xopL// <sub>Xcc8004</sub> gene is positively regulated by HrpG/HrpX (Yan //et al//., 2019).
=== Phenotypes ===

  * XopL<sub>Xcv85-10</sub>  displays E3 ubiquitin ligase activity and inhibits expression of the elf18- and flg22-induced defense gene pNHL10 in //Arabidopsis//  mesophyll protoplasts, triggers cell death in //Nicotiana benthamiana//  and suppresses PTI in host plants (Singer //et al//., 2013; Popov //et al//., 2016).
  * In contrast, XopL<sub>Xoc</sub>  does not induce cell death in //N. benthamiana//. FIXME
  * XopL<sub>Xcc8004</sub>  is required for full virulence and growth of //X. campestris//  pv. //campestris//  in the host plant Chinese radish (Jiang //et al.//, 2009).
  * XopL<sub>Xcv85-10</sub>  suppresses PAMP-related defense gene expression and is an E3 ubiquitin ligase (Singer //et al//., 2013).
  * Transient expression of XopL, led to a nearly complete elimination of stromules and the relocation of plastids to the nucleus and further characterization of XopL revealed that the E3 ligase activity is essential for two plastid phenotypes (Erickson //et al//., 2016).
  * XopL<sub>Xap</sub>  is a T3E which supports //X. axonopodis//  pv. //punicae//  for multiplication in pomegranate by suppressing plant immune responses including plant cell death (Soni //et al//., 2017).
  * XopL<sub>Xcc8004</sub>  interferes with innate immunity of //Arabidopsis//  (Yan //et al//., 2019).
  * //Xcv//  strain 85-10 suppresses host autophagy by utilizing type-III effector XopL. Intriguingly, XopL is targeted for degradation by defense-related selective autophagy mediated by NBR1/Joka2, revealing a complex antagonistic interplay between XopL and the host autophagy machinery (Leong //et al.//, 2022).
=== Localization ===

Possibly plasma membrane. The transiently expressed XopL<sub>Xap</sub>::EYFP fusion protein was localized to the plasma membrane, indicating the possible site of its action (Soni //et al//., 2017).

=== Enzymatic function ===

E3 ubiquitin ligase activity (Singer //et al//., 2013).

=== Interaction partners ===

XopL<sub>//Xcv//85-10</sub>  interacts with and degrades the autophagy component SH3P2 via its E3 ligase activity to promote infection (Leong //et al.//, 2022).

===== Conservation =====

=== In xanthomonads ===

Yes (//e.g.//, //X. euvesicatoria//, //X. citri//, //X. axonopodis//, //X. oryzae//, //X. oryzicola//, //X//. //fragariae//, //X//. //perforans, X. gardneri//, //X. campestris// pv. //campestris//, but not //X. campestris// pv. //raphani//, in some //X. arboricola// pathovars). See for example [[https://doi.org/10.1094/MPMI-22-11-1401|Table 2]] in Jiang //et al//. (2009) and [[https://doi.org/10.1371/journal.ppat.1003121.s001|Figure S1]] in Singer //et al//. (2013).
=== In other plant pathogens/symbionts ===

No.

===== References =====

Adlung N (2016). Charakterisierung der Avirulenzaktivität von XopQ und Identifizierung möglicher Interaktoren von XopL aus //Xanthomonas campestris// pv. //vesicatoria//. Doctoral Thesis. Martin-Luther-Universität Halle-Wittenberg, Germany. PDF: [[https://d-nb.info/1116951061/34|d-nb.info/1116951061/34]] FIXME

Erickson JL, Adlung N, Lampe C, Bonas U, Schattat MH (2018). The //Xanthomonas// effector XopL uncovers the role of microtubules in stromule extension and dynamics in //Nicotiana benthamiana//. Plant J. 93: 856-870. DOI:[[https://doi.org/10.1111/tpj.13813|10.1111/tpj.13813]]

Jiang W, Jiang BL, Xu RQ, Huang JD, Wei HY, Jiang GF, Cen WJ, Liu J, Ge YY, Li GH, Su LL, Hang XH, Tang DJ, Lu GT, Feng JX, He YQ, Tang JL (2009). Identification of six type III effector genes with the PIP box in //Xanthomonas campestris// pv //campestris// and five of them contribute individually to full pathogenicity. Mol. Plant Microbe Interact. 22: 1401-1411. DOI: [[https://doi.org/10.1094/MPMI-22-11-1401|10.1094/MPMI-22-11-1401]]

Leong JX, Raffeiner M, Spinti D, Langin G, Franz-Wachtel M, Guzman AR, Kim JG, Pandey P, Minina AE, Macek B, Hafrén A, Bozkurt TO, Mudgett MB, Börnke F, Hofius D, Üstün S (2022). A bacterial effector counteracts host autophagy by promoting degradation of an autophagy component. EMBO J. 41: e110352. DOI: [[https://doi.org/10.15252/embj.2021110352|10.15252/embj.2021110352]]

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]]

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: [[https://doi.org/10.1094/MPMI-07-16-0137-R|10.1094/MPMI-07-16-0137-R]]

Singer AU, Schulze S, Skarina T, Xu X, Cui H, Eschen-Lippold L, Egler M, Srikumar T, Raught B, Lee J, Scheel D, Savchenko A, Bonas U (2013). A pathogen type III effector with a novel E3 ubiquitin ligase architecture. PLoS Pathog. 9: e1003121. DOI: [[https://doi.org/10.1371/journal.ppat.1003121|10.1371/journal.ppat.1003121]]

Soni M, Mondal KK. (2017). //Xanthomonas axonopodis// pv. //punicae// employs XopL effector to suppress pomegranate immunity. J. Integr. Plant Biol. 60: 341-357. DOI: [[https://doi.org/10.1111/jipb.12615|10.1111/jipb.12615]]

Yan X, Tao J, Luo HL, Tan LT, Rong W, Li HP, He CZ (2019). A type III effector XopL<sub>Xcc8004</sub> is vital for //Xanthomonas campestris// pathovar //campestris// to regulate plant immunity. Res. Microbiol. 170: 138-146. DOI: [[https://doi.org/10.1016/j.resmic.2018.12.001|10.1016/j.resmic.2018.12.001]]