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

Author: [[https://www.researchgate.net/profile/Ralf_Koebnik|Ralf Koebnik]]\\
Expert reviewer: [[https://www.researchgate.net/profile/Frederik-Boernke|Frederik Börnke]]

Class: XopM\\
Family: XopM\\
Prototype: XCV0442 (//Xanthomonas euvesicatoria// pv. //euvesicatoria//, ex //Xanthomonas campestris// pv. //vesicatoria//; strain 85-10)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_011346113.1|WP_011346113.1]]\\
3D structure: Unknown

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

=== How discovered? ===

//xopM// <sub>//Xee//85-10</sub> was identified as a candidate T3E gene based on the presence of a PIP box in the promoter region and its conservation in other plant pathogens (Schulze //et al.//, 2012). XopM was also discovered as a T3E in //Xee//<sub>85-10</sub> using a machine-learning approach (Teper //et al//., 2016).

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

//Xanthomonas// bacteria containing a translational fusion between XopM and an N-terminally truncated variant of AvrBs3 were shown by imumunodetection with an AvrBs3-specific antibody to secrete the chimeric protein into the culture medium in a T3SS-dependent manner (Schulze //et al.//, 2012).

To test for T3SS-dependent translocation into plant cells, //Xee// <sub>85-10</sub> expressing the XopM-AvrBs3 chimeric protein was inoculated into leaves of AvrBs3-responsive pepper plants (ECW-30R) and the near-isogenic susceptible pepper line ECW, which lacks the //Bs3// resistance gene. Bacteria expressing the XopM<sub>1–520</sub>-AvrBs3delta2 chimeric protein induced the hypersensitive response (HR) in ECW-30R, but not in ECW. As expected, no HR induction was observed in plants infected with a strain mutated in the T3SS gene //hrcV// (Schulze //et al.//, 2012).

=== Regulation ===

Expression of //xopM// <sub>//Xee//85-10</sub> was shown to be controlled by both HrpG and HrpX (Schulze //et al.//, 2012).

=== Phenotypes ===

The //Xee//<sub>85-10</sub> strain deleted in //xopM// showed no difference in the induction of disease symptoms on pepper plants compared to the wild-type strain 85-10 (Schulze //et al.//, 2012).

To identify defense reactions, mediated by //xopM//, leaves of pepper ECW, //Nicotiana benthamiana// and //N. tabacum//, the latter two being nonhost plants of //Xee// <sub>85-10</sub>, were inoculated with //Agrobacterium// strains mediating the //in planta// expression of the effector gene fused to GFP. In this assay, XopM elicited a cell death reaction in //N. benthamiana// at 3–5 dpi (Schulze //et al.//, 2012).
When ectopically expressed in plants, XopM supports growth of a non-pathogenic bacterial strain and dampens the production of reactive oxygen species, indicating its ability to suppress plant immunity (Brinkmann et al., 2024). The abilty to repress a flg22 induced ROS burst is independent of XopM binding to VAP but requires localization at the host cell plasma membrane (see below, Brinkmann et al., 2024).

=== Localization ===

XopM-GFP fusions have been shown to localize to the plant plasma membrane (PM) in //N. benthamiana// leaf epidermal cells. Possibly concentrated in ER-PM contact sites (Brinkmann //et al//., 2024)
=== Enzymatic function ===

Unknown.

=== Interaction partners ===

XopM interacts with vesicle-associated membrane protein (VAMP)-associated proteins (VAPs) in an isoform specific manner. XopM displays two FFAT [two phenylalanines (FF) in an acidic tract (AT)] motifs that cooperatively mediate the interaction with VAP. Binding to VAP is not required for XopM's ability to suppress PTI, indicating that it has other virulence targets. //In planta// pull-down assays using XopM-GFP as a bait, suggest that it interacts with additional membrane components (Brinkmann //et al//., 2024).

===== Conservation =====

=== In xanthomonads ===

//xopM// is typically encoded next to the //hrp// gene cluster and considered a core effector gene in several //Xanthomonas// species (Jiang //et al.//, 2009; Merda //et al.//, 2017; Pesce //et al.//, 2017).
=== In other plant pathogens/symbionts ===

Yes (//Acidovorax//, //Pseudomonas//, and //Ralstonia//) (Schulze //et al.//, 2012; Pesce //et al.//, 2017)
===== References =====

Brinkmann C, Bortlik J, Raffeiner M, González-Fuente M, Börnke LF, Üstün S, Börnke F (2024). XopM, an FFAT motif-containing type III effector protein from //Xanthomonas//, suppresses MTI responses at the plant plasma membrane. Mol. Plant Pathol. 25: e70038. DOI: [[https://doi.org/10.1111/mpp.70038|10.1111/mpp.70038]]

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]]

Pesce C, Jacobs JM, Berthelot E, Perret M, Vancheva T, Bragard C, Koebnik R (2017). Comparative genomics identifies a novel conserved protein, HpaT, in proteobacterial type III secretion systems that do not possess the putative translocon protein HrpF. Front. Microbiol. 8: 1177. DOI: [[https://doi.org/10.3389/fmicb.2017.01177|10.3389/fmicb.2017.01177]]

Merda D, Briand M, Bosis E, Rousseau C, Portier P, Barret M, Jacques MA, Fischer-Le Saux M (2017). Ancestral acquisitions, gene flow and multiple evolutionary trajectories of the type three secretion system and effectors in Xanthomonas plant pathogens. Mol. Ecol. 26: 5939-5952. DOI: [[https://doi.org/10.1111/mec.14343|10.1111/mec.14343]]

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]]

Teper D, Burstein D, Salomon D, Gershovitz M, Pupko T, Sessa G (2016). Identification of novel //Xanthomonas euvesicatoria// type III effector proteins by a machine-learning approach. Mol. Plant Pathol. 17: 398-411. DOI: [[https://doi.org/10.1111/mpp.12288|10.1111/mpp.12288]]