====== The Type III Effector XopK from //Xanthomonas// ======

Author: [[https://www.researchgate.net/profile/Joel_Pothier2|Joël F. Pothier]] & Trainees from the 2<sup>nd</sup>  EuroXanth Training School ([[https://www.researchgate.net/profile/Amandine_Cunty|Amandine Cunty]], [[https://www.researchgate.net/profile/Filip_Gazdik|Filip Gazdik]], [[https://www.researchgate.net/profile/Leonor_Martins|Leonor Martins]], Cinzia Van Malderghem, Esther Van Veen)\\
Internal reviewer: [[https://www.researchgate.net/profile/Alexandre_Menezes6|Alexandre B. de Menezes]]\\
Expert reviewer: Rebecca Bart

Class: XopK\\
Family: XopK\\
Prototype: XOO1669 (//Xanthomonas oryzae// pv. //oryzae//; strain T7174)\\
GenBank ID: [[https://www.ncbi.nlm.nih.gov/protein/BAE68424.1|BAE68424.1]] (845 aa)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_027703763.1|WP_027703763.1]] (843 aa)\\
3D structure: Unknown

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

=== How discovered? ===

XopK was discovered as a putative T3E based on the presence of a plant-inducible promoter box-like sequence and a -10 box-like sequence (Furutani //et al//., 2006).
=== (Experimental) evidence for being a T3E ===

Mutation of a putative ubiquitin-conjugation enzyme (E2) binding site abolished XopK-induced degradation of rice somatic receptor kinase 2 (OsSERK2) and compromised XopK-dependent virulence (Qin //et al//., 2018). Expression of XopK is HrpX-dependent (Furutani //et al//., 2006) and was observed to translocate using a Cya reporter system (Furutani //et al//., 2009).
=== Regulation ===

Preceded by both a PIP box and a -10 box-like motif (Schulze //et al//., 2012; Furutani //et al//., 2006).

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 //xopK//, 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).
=== Phenotypes ===

  * Deletion of XopK has been shown not to affect the virulence of //X. oryzae//  pv. //oryzae//  PXO99A in rice IR24 plants; these differential results could be attributed to different genotypes of the rice cultivar or field conditions for plant growth (Song & Yang, 2010).
  * A ∆//xopK//  mutant strain of //Xanthomonas phaseoli//  pv. //manihotis//  (aka //Xanthomonas axonopodis//  pv. //manihotis//) exhibited enhanced induction of disease symptoms in cassava at the site of inoculation but reduced spread through the vasculature (Mutka //et al.//, 2016).
  * XopK inhibits pathogen-associated molecular pattern-triggered immunity upstream of mitogen-activated protein kinase cascades (Qin //et al.//, 2018)

=== Localization ===

The XopK sequence contains 54% hydrophobic residues and several predicted transmembrane domains. Thus, it is possible this protein is associated with host cell membranes following secretion (Mutka //et al//., 2016)

=== Enzymatic function ===

The protein has E3 ubiquinol ligase activity. The putative E2-binding site is highly conserved in the majority of members from different //Xanthomonas//  strains except for //X. oryzae//  pv. oryzicola strains (W420C).

=== Interaction partners ===

XopK interacted with and directly ubiquitinated rice somatic embryogenic receptor kinase 2 (OsSERK2), resulting in its degradation (Qin //et al//., 2018)

===== Conservation =====

=== In xanthomonads ===

Yes (based on EDGAR; e.g., //X. oryzae//  pvs. oryzae and oryzicola, //X. citri//  pvs. citri, malvacearum, fuscans and glycines, //X. euvesicatoria//, //X. perforans//, //X. campestris//, //X. cynarae//  pv. gardneri, //X. fragariae//, //X. translucens//, //X. vesicatoria//). In addition to the taxa above, BLAST against the GenBank nt database also shows matches to// X. arboricola, X. hortorum, X. hyacinthi//.

=== In other plant pathogens/symbionts ===

Yes (e.g., //Acidovorax//  spp. with 42% AAI). BLAST against GenBank nt DB suggests that //Acidovorax s//pp. is the only group in which this gene may be present outside Xanthomonadaceae.

===== References =====

Furutani A, Nakayama T, Ochiai H, Kaku H, Kubo Y, Tsuge S (2006). Identification of novel HrpXo regulons preceded by two //cis//-acting elements, a plant-inducible promoter box and a -10 box-like sequence, from the genome database of //Xanthomonas oryzae//  pv. oryzae. FEMS Microbiol. Lett. 259: 133-141. DOI: [[https://doi.org/10.1111/j.1574-6968.2006.00265.x|10.1111/j.1574-6968.2006.00265.x]]

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]]

Mutka AM, Fentress SJ, Sher SW, Berry JC, Pretz C, Nusinow DA, Bart R (2016). Quantitative, image-based phenotyping methods provide insight into spatial and temporal dimensions of plant disease. Plant Physiol. 172: 650-660. DOI: [[https://doi.org/10.1104/pp.16.00984|10.1104/pp.16.00984]]

Qin J, Zhou X, Sun L, Wang K, Yang F, Liao H, Rong W, Yin J, Chen H, Chen X, Zhang J (2018). The //Xanthomonas//  effector XopK harbours E3 ubiquitin-ligase activity that is required for virulence. New Phytol. 220: 219-231. DOI: [[https://doi.org/10.1111/nph.15287|10.1111/nph.15287]]

Schulze S, Kay S, Büttner D, Egler M, Eschen-Lippold L, Hause G, Krüger A, Lee J, Müller O, Scheel D, Szczesny R, Thieme F, Bonas U (2012). Analysis of new type III effectors from //Xanthomonas//  uncovers XopB and XopS as suppressors of plant immunity. New Phytol. 195: 894-911. DOI: [[https://doi.org/10.1111/j.1469-8137.2012.04210.x|10.1111/j.1469-8137.2012.04210.x]]

Song C, Yang B (2010). Mutagenesis of 18 type III effectors reveals virulence function of XopZ<sub>PXO99</sub>  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]]

===== Acknowledgements =====

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