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

Author: [[https://www.researchgate.net/profile/Laurent_Noel|Laurent D. Noël]]\\
Internal reviewer: [[https://www.researchgate.net/profile/Ralf_Koebnik|Ralf Koebnik]]\\
Expert reviewer: [[https://www.researchgate.net/profile/Jian-Min_Zhou|Jian-Min Zhou]]\\

Class: XopAC\\
Family: XopAC\\
Prototype: XopAC (//Xanthomonas campestris// pv. //campestris//; strain 8004)\\
GenBank ID: [[https://www.ncbi.nlm.nih.gov/protein/AFP74845.1|AFP74845.1]] (536 aa)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_011269629.1|WP_011269629.1]] (536 aa)\\
3D structure: Unknown

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

=== How discovered? ===

XopAC/AvrAC was identified as a putative type III effector because of the presence of seven prokaryotic-type leucine-rich repeats in its C-terminal domain and a PIP-box motif in the //xopAC// promoter suggestive of a //hrpX//-dependent expression (Xu //et al//., 2008).

=== (Experimental) evidence for being a T3E ===

The N-terminal region of XopAC (XopAC<sub>1-217</sub>) mediates secretion and translocation of an AvrBs1 reporter domain (AvrBs1<sub>59-445</sub>) into pepper leaves in a //hrpF//-dependent manner (Xu //et al//., 2008).

=== Regulation ===

//xopAC// promoters possess a PIP-box motif (Xu //et al//., 2008). Expression of //xopAC// is induced in the //hrp//-inducing medium XVM2 in a //hrpG//- and //hrpX//-dependent manner (Xu //et al//., 2008).

=== Phenotypes ===

  * //xopAC//, also named //avrAC//, confers avirulence to //Xanthomonas campestris// pv. //campestris// (//Xcc//) on //Arabidopsis// accession Col-0 but not on Kas (Xu //et al//., 2008).
  * //xopAC// avirulence is weak in mesophyll tissue but strong upon inoculation of hydathodes or vascular tissues (Xu //et al//., 2008; Cerutti //et al//., 2017).
  * //xopAC// contributes to //Xcc// pathogenicity on //Brassica oleracea// and //Arabidopsis// in a //BIK1//-dependent manner (Feng //et al//., 2012).
  * XopAC inhibits BIK1 kinase activity and blocks flg22-induced PTI responses (Feng //et al//., 2012).
  * XopAC was found to be associated with variations in disease symptoms when testing a set of 45 //Xcc// strains on two natural accessions of //Arabidopsis// (Guy //et al.//, 2013a).
  * Mutagenesis of type III effectors in //Xcc// confirmed that //xopAC// functions as both a virulence and an avirulence gene in //Arabidopsis// (Guy et al., 2013).
  * When heterologously expressed in virulent //Ralstonia solanacearum// or //Pseudomonas syringae// pv. //tomato//, XopAC confers avirulence on the //Arabidopsis// accession Col-0 (Guy //et al//., 2013b).
  * Transgenic expression of //xopAC// in //Arabidopsis// accession Col-0 induces early growth arrest at both apical and root meristems (Wang //et al//., 2015).
  * AvrAC recognition requires the RKS1 pseudokinase of the ZRK family and the NLR protein ZAR1, which also recognizes the //Pseudomonas syringae// effectors HopZ1a, HopBA1, HopF1, HopO1, and HopX1 and the //Xanthomonas perforans//effector XopJ4 (Wang //et al.//, 2015; Laflamme //et al.//, 2020; Schultink //et al.//, 2019).

=== Localization ===

XopAC was localized to the plant plasma membrane upon //Agrobacterium//-mediated transient expression in //Nicotiana benthamiana// (Guy //et al//., 2013b). This localization depends on its LRR domain suggesting that XopAC localization is dependent on its interacting partner(s) (Guy //et al//., 2013b).

=== Enzymatic function ===

XopAC presents an uridylyl transferase activity, which depends on residue H<sub>469</sub> (Feng //et al//., 2012). XopAC is able to uridylylate both conserved S<sub>236</sub> and T<sub>237</sub> in BIK1. Similar activity was demonstrated for all other RLCK VIIa tested including PBL2, which acts as a decoy and enables AvrAC detection (Feng //et al//., 2012; Wang //et al//., 2015).

=== Interaction partners ===

Nine //Arabidopsis// RLCKs (receptor-like cytoplasmic kinases, subfamily VIIa) were described as putative interactors of XopAC using yeast-two hybrid assays (Guy //et al//., 2013b). Importantly, PBL2 RLCK is essential for the XopAC avirulence function and BIK1 RLCK is required for the XopAC virulence functions (Guy //et al//., 2013b; Feng //et al//., 2012; Wang //et al//., 2015).

===== Conservation =====

=== In xanthomonads ===

xopAC is present in many //Xcc// strains as well as several //Xanthomonas campestris// pv. //raphani// (Guy //et al//., 2013a). To date, all allelic variants of XopAC conferred avirulence in //Arabidopsis// accession Col-0 (Guy //et al//., 2013b).

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

Yes, //Ralstonia solanacearum// (Tan //et al.//, 2019).

===== References =====

Cerutti A, Jauneau A, Auriac M-C, Lauber E, Martinez Y, Chiarenza S, Leonhardt N, Berthomé R, Noël LD (2017). Immunity at cauliflower hydathodes controls infection by //Xanthomonas campestris// pv. //campestris//. Plant Physiol. 174: 700-712. DOI: [[https://doi.org/10.1104/pp.16.01852|10.1104/pp.16.01852]]

Feng F, Yang F, Rong W, Wu X, Zhang J, Chen S, He C, Zhou JM (2012). A //Xanthomonas// uridine 5'-monophosphate transferase inhibits plant immune kinases. Nature 485: 114-118. DOI: [[https://doi.org/10.1038/nature10962|10.1038/nature10962]]

Guy E, Genissel A, Hajri A, Chabannes M, David P, Carrère S, Lautier M, Roux B, Boureau T, Arlat M, Poussier S, Noël LD (2013a). Natural genetic variation of //Xanthomonas campestris// pv. campestris pathogenicity on //Arabidopsis// revealed by association and reverse genetics. MBio 4: e00538-12. DOI: [[https://doi.org/10.1128/mBio.00538-12|10.1128/mBio.00538-12]]. Erratum in: MBio (2013) 4: e00978-13.

Guy E, Lautier M, Chabannes M, Roux B, Lauber E, Arlat M, Noël LD (2013b). //xopAC//-triggered immunity against //Xanthomonas// depends on //Arabidopsis// receptor-like cytoplasmic kinase genes //PBL2// and //RIPK//. PLoS One 8: e73469. DOI: [[https://doi.org/10.1371/journal.pone.0073469|10.1371/journal.pone.0073469]]

Laflamme B, Dillon MM, Martel A, Almeida RND, Desveaux D, Guttman DS (2020). The pan-genome effector-triggered immunity ladscape of a host-pathogen interaction. Science 367: 763-768. DOI: [[http://doi.org/10.1126/science.aax4079|10.1126/science.aax4079]]

Schultink A, Qi T, Bally J, Staskawicz B (2019). Using forward genetics in //Nicotiana benthamiana// to uncover the immune signaling pathway mediating recognition of the //Xanthomonas perforans// effector XopJ4. New Phytol. 221: 1001-1009. DOI: [[http://doi.org/doi: 10.1111/nph.15411| 10.1111/nph.15411]]

Tan X, Qiu H, Li F, Cheng D, Zheng X, Wang B, Huang M, Li W, Li Y, Sang K, Song B, Du J, Chen H, Xie C (2019). Complete genome sequence of sequevar 14M //Ralstonia solanacearum// strain HA4-1 reveals novel type III effectors acquired through horizontal gene transfer. Front. Microbiol. 10: 1893. DOI: [[https://doi.org/10.3389/fmicb.2019.01893|10.3389/fmicb.2019.01893]]

Wang G, Roux B, Feng F, Guy E, Li L, Li N, Zhang X, Lautier M, Jardinaud MF, Chabannes M, Arlat M, Chen S, He C, Noël LD, J.M. Zhou JM (2015). The decoy substrate of a pathogen effector and a pseudokinase specify pathogen-induced modified-self recognition and immunity in plants. Cell Host Microbe 18: 285-295. DOI: [[https://doi.org/10.1016/j.chom.2015.08.004|10.1016/j.chom.2015.08.004]]

Xu RQ, Blanvillain S, Feng JX, Jiang BL, Li XZ, Wei HY, Kroj T, Lauber E, Roby D, Chen B, He YQ, Lu GT, Tang DJ, Vasse J, Arlat M, Tang JL (2008). AvrAC<sub>Xcc8004</sub>, a type III effector with a leucine-rich repeat domain from //Xanthomonas campestris// pathovar //campestris// confers avirulence in vascular tissues of //Arabidopsis thaliana// ecotype Col-0. J. Bacteriol. 190: 343-355. DOI: [[https://doi.org/10.1128/JB.00978-07|10.1128/JB.00978-07]]

===== Acknowledgements =====

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