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

Author: [[https://www.researchgate.net/profile/Ralf-Koebnik|Ralf Koebnik]]

Class: XopAI\\
Family: XopAI\\
Prototype: XAC3230 (//Xanthomonas citri// pv. //citri//; strain 306)\\
GenBank ID: [[https://www.ncbi.nlm.nih.gov/protein/AAM38074.1|AAM38074.1]] (296 aa)\\
RefSeq ID: [[https://www.ncbi.nlm.nih.gov/protein/WP_011052119.1|WP_011052119.1]] (296 aa)\\
3D structure: [[https://www.rcsb.org/structure/6K93|6K93]], [[https://www.rcsb.org/structure/6K94|6K94]], [[https://www.rcsb.org/structure/6KLY|6KLY]] (Liu //et al.//, 2019)

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

=== How discovered? ===

Based on the complete genome sequence, XopAI (XAC3230) was proposed as a Hrp regulon candidate (da Silva //et al.//, 2002).

Co-regulation of //xopAI// with other HrpG-controlled genes was also proposed by Noël //et al.// (2006) based on the observation that 200 bp of the 5' sequence including promoter and coding regions of //xopE2// (//avrXacE3//) and //xopAI// (XAC3230) from //X. citri //pv. //citri// are more than 85% identical to the corresponding region of //xopJ//, which is a member of the HrpG regulon from //X. euvesicatoria// pv. //euvesicatoria// (ex //X. campestris// pv. //vesicatoria//).

Based on homology to effectors from //Pseudomonas syringae// and a strongly conserved 43‐amino‐acid N‐terminal domain that is also found in the N‐termini of effectors in class XopE and XopJ, XopAI was proposed to be a T3E (Stavrinides //et al.//, 2006; White //et al.//, 2009).
=== (Experimental) evidence for being a T3E ===

Unknown.

=== Regulation ===

Using microarrays, seven T3E genes from //X. citri //pv. //citri// were found to be upregulated in planta, five of which in all the three times investigated, i.e. 24 hpi, 72 hpi and 120 hpi (//xopE1//, //xopN//, //xopK//, //xopE3//, //xopAI//), and the two remaining at the later times of the infectious process (//xopE2// and //xopV//) (de Laia //et al.//, 2019).
=== Phenotypes ===

Unknown.

=== Localization ===

The XopAI N‐terminal domain contains a myristoylation motif, which was previously identified in several T3Es of //P. syringae//, indicating that effectors with this N‐terminal domain are targeted to host cellular membranes (White //et al.//, 2009).
=== Enzymatic function ===

The C-terminal region of XopAI has similarity to predicted ADP-ribosyl transferase domains of the effector HopO1-1 of //Pseudomonas syringae// (Moreira //et al.//, 2010).

XopAI was predicted to be a member of the arginine-specific mono-ADP-ribosyltransferase (mART) family. However, the crystal structure of XopAI revealed an altered active site that is unsuitable to bind the cofactor NAD+, but with the capability to capture an arginine-containing peptide from XopAI itself. Based on this finding, it was proposed that XopAI may not be a qualified mART, and it would exert different effects on host cells (Liu //et al.//, 2019).

Structural homologs of XopAI are, among others, the HopU1 (//Pseudomonas syringae// T3SS-secreted effector HopU1, PDB code [[https://www.rcsb.org/structure/3U0J|3U0J]]), Tre1 (//Serratia proteamaculans// T6SS-secreted ADP-ribosyltransferase effector 1, PDB code [[https://www.rcsb.org/structure/6DRH|6DRH]]), ART2.2 (rat mART2.2, PDB code [[https://www.rcsb.org/structure/1GXY|1GXY]]), and ExoS (//Pseudomonas// //aeruginosa// exoenzyme S, PDB code [[https://www.rcsb.org/structure/6GN8|6GN8]]) (Liu //et al.//, 2019).
=== Interaction partners ===

===== Conservation =====

=== In xanthomonads ===

XopAI is conserved in the Citrus canker strains, including //X. citri// pv. //citri// and //X. citri// pv. //aurantifolii // (ex //X. fuscans// pv. //aurantifolii//) (Moreira //et al.//, 2010). However, XopAI is absent from the Citrus bacterial spot pathogen, //X. euvesicatoria// pv. //citrumelonis// (ex //X. axonopodis// pv. //citrumelo//) strain F1 (Jalan //et al.//, 2011).

XopAI homologs were also found in //X. citri// pv. //bilvae// and //X. citri// pv. //glycines//, as well as in the species //X. arboricola//, //X. hortorum//, //X. vesicatoria// (Moreira //et al.//, 2010;  Liu //et al.//, 2019).
=== In other plant pathogens/symbionts ===

Yes (e.g., //Acidovorax citrulli//, //Pseudomonas syringae//, //Ralstonia solanacearum//) (Moreira //et al.//, 2010)

===== References =====

da Silva AC, Ferro JA, Reinach FC, Farah CS, Furlan LR, Quaggio RB, Monteiro-Vitorello CB, Van Sluys MA, Almeida NF, Alves LM, do Amaral AM, Bertolini MC, Camargo LE, Camarotte G, Cannavan F, Cardozo J, Chambergo F, Ciapina LP, Cicarelli RM, Coutinho LL, Cursino-Santos JR, El-Dorry H, Faria JB, Ferreira AJ, Ferreira RC, Ferro MI, Formighieri EF, Franco MC, Greggio CC, Gruber A, Katsuyama AM, Kishi LT, Leite RP, Lemos EG, Lemos MV, Locali EC, Machado MA, Madeira AM, Martinez-Rossi NM, Martins EC, Meidanis J, Menck CF, Miyaki CY, Moon DH, Moreira LM, Novo MT, Okura VK, Oliveira MC, Oliveira VR, Pereira HA, Rossi A, Sena JA, Silva C, de Souza RF, Spinola LA, Takita MA, Tamura RE, Teixeira EC, Tezza RI, Trindade dos Santos M, Truffi D, Tsai SM, White FF, Setubal JC, Kitajima JP (2002). Comparison of the genomes of two //Xanthomonas// pathogens with differing host specificities. Nature 417: 459-463. DOI: [[https://doi.org/10.1038/417459a|10.1038/417459a]]

de Laia ML, Moreira LM, Gonçalves JF, Ferro MI, Pinto Rodrigues AC, dos Santos JN, Felestrino ÉB, Ferro JA (2019). Gene expression analysis identifies hypothetical genes that may be critical during the infection process of //Xanthomonas citri// subsp. //citri//.\\
Electron. J. Biotechnol. 42: 30-41. DOI: 10.1016/j.ejbt.2019.10.003

Fu Z (2008). //Pseudomonas syringae// type III secretion system and effectors. PhD thesis, University of Nebraska, Lincoln, USA.

Gaurav I, Thakur A, Kumar G, Long Q, Zhang K, Sidu RK, Thakur S, Sarkar RK, Kumar A, Iyaswamy A, Yang Z (2023). Delivery of apoplastic extracellular vesicles encapsulating green-synthesized silver nanoparticles to treat citrus canker. Nanomaterials (Basel) 13: 1306. DOI: [[https://doi.org/10.3390/nano13081306|10.3390/nano13081306]]

Jalan N, Aritua V, Kumar D, Yu F, Jones JB, Graham JH, Setubal JC, Wang N (2011). Comparative genomic analysis of //Xanthomonas axonopodis// pv. //citrumelo// F1, which causes citrus bacterial spot disease, and related strains provides insights into virulence and host specificity. J. Bacteriol. 193: 6342-6357. DOI: [[https://doi.org/10.1128/JB.05777-11|10.1128/JB.05777-11]]

Liu JH, Yang JY, Hsu DW, Lai YH, Li YP, Tsai YR, Hou MH (2019). Crystal structure-based exploration of arginine-containing peptide binding in the ADP-ribosyltransferase domain of the type III effector XopAI protein. Int. J. Mol. Sci. 20: 5085. DOI: [[https://doi.org/10.3390/ijms20205085|10.3390/ijms20205085]]

Moreira LM, Almeida NF Jr, Potnis N, Digiampietri LA, Adi SS, Bortolossi JC, da Silva AC, da Silva AM, de Moraes FE, de Oliveira JC, de Souza RF, Facincani AP, Ferraz AL, Ferro MI, Furlan LR, Gimenez DF, Jones JB, Kitajima EW, Laia ML, Leite RP Jr, Nishiyama MY, Rodrigues Neto J, Nociti LA, Norman DJ, Ostroski EH, Pereira HA Jr, Staskawicz BJ, Tezza RI, Ferro JA, Vinatzer BA, Setubal JC (2010). Novel insights into the genomic basis of citrus canker based on the genome sequences of two strains of //Xanthomonas fuscans// subsp. //aurantifolii//. BMC Genomics 11: 238. DOI: [[https://doi.org/10.1186/1471-2164-11-238|10.1186/1471-2164-11-238]]

Noël L, Thieme F, Gäbler J, Büttner D, Bonas U (2003). XopC and XopJ, two novel type III effector proteins from Xanthomonas campestris pv. vesicatoria. J. Bacteriol. 185: 7092-7102. DOI: [[https://doi.org/10.1128/JB.185.24.7092-7102.2003|10.1128/JB.185.24.7092-7102.2003]]

Stavrinides J, Ma W, Guttman DS (2006). Terminal reassortment drives the quantum evolution of type III effectors in bacterial pathogens. PLoS Pathog. 2: e104. DOI: [[https://doi.org/10.1371/journal.ppat.0020104|10.1371/journal.ppat.0020104]]

White FF, Potnis N, Jones JB, Koebnik R (2009). The type III effectors of //Xanthomonas//. Mol. Plant Pathol. 10: 749-766. DOI: [[https://doi.org/10.1111/j.1364-3703.2009.00590.x|10.1111/j.1364-3703.2009.00590.x]]