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

Author: [[https://www.researchgate.net/profile/Christian_Verniere|Christian Vernière ]] & Trainees from the 2<sup>nd</sup>  EuroXanth Training School ([[https://www.researchgate.net/profile/Songul_Erken|Songül Erken]], [[https://www.researchgate.net/profile/Damla_Ertimurtas|Damla Ertimurtaş]], [[https://www.researchgate.net/profile/Jelena_Menkovic|Jelena Menković]], [[https://www.researchgate.net/profile/Andjelka_Prokic|Andjelka Prokić]])\\
Internal reviewer: [[https://www.researchgate.net/profile/Tamas_Kovacs6|Tamás Kovács]]\\
Expert reviewer: [[https://www.researchgate.net/profile/Nian-Wang|Nian Wang]]

Class: XopAG\\
Family: XopAG1, XopAG2\\
Prototype: AvrGf1 (//Xanthomonas citri// pv. //citri//; Xac‐A<sup>w</sup>  strain 12879), AvrGf2 (//Xanthomonas fuscans// pv. //aurantifolii//; Xac‐A<sup>w</sup>  strain Xfa-C51302)\\
GenBank ID (AvrGf1): [[https://www.ncbi.nlm.nih.gov/protein/ABB84189.1|ABB84189.1]] (532 aa)\\
GenBank ID (AvrGf2): [[https://www.ncbi.nlm.nih.gov/protein/AIP90071.1|AIP90071.1]] (508 aa)\\
RefSeq ID (XopAG1): [[https://www.ncbi.nlm.nih.gov/protein/WP_272820829.1|WP_272820829.1]] (511 aa)\\
RefSeq ID (XopAG2): [[https://www.ncbi.nlm.nih.gov/protein/WP_007970248.1|WP_007970248.1]] (508 aa)\\
Synonym: AvrGf1, AvrGf2\\
3D structure: Unknown

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

=== How discovered? ===

//Xanthomonas citri// pv. //citri// (Xcc-A) causing citrus bacterial canker can infect most of the commercial citrus species and are worldwide distributed. Strains that were pathogenic on Key lime (//Citrus aurantifolia//), but that did not cause canker symptoms on grapefruit, were reported in Florida and designated as Xcc-A<sup>w</sup>  . Three clones were selected from a genomic library of the 12879 strain of Xcc-A<sup>w</sup>  that caused rapid necrosis in grapefruit leaves, but not in tomato leaves when they were expressed in //X. perforans// (Rybak //et al.//, 2009). A 1599-bp open reading frame (ORF) was found within the nucleotide sequence of DNA from a 2.3-kb subclone from pL799 that caused HR in grapefruit leaves. The complete sequence of the ORF, designated as //avrGf1// (Rybak //et al.//, 2009). Genes //avrGf1// and //avrGf2// were found to share low sequence similarity at the nucleotide level, except for a small region in the last 200 nucleotides of the genes, which showed a high level of identity (68%) (Gochez //et al.//, 2017). The alignment of translated proteins AvrGf1 (533 amino acids) and AvrGf2 (509 amino acids) determined that AvrGf2 had a low degree of sequence identity (45% amino acid identity) with the previously identified AvrGf1. The highest sequence similarities were observed between AvrGf1 and AvrGf2 in the C-terminal portions of the effector proteins (74.5% identity at the amino acid level over 51 amino acids) (Gochez //et al.//, 2017).
=== (Experimental) evidence for being a T3E ===

An active TTSS is necessary for HR produced by AvrGf1 in grapefruit leaves, as it was proven by transconjugation experiments (Rybak //et al.//, 2009).
=== Regulation ===

No data available. The effector gene //xopAG// was however shown to be induced in XVM2 medium compared to NB medium in X. citri subsp. citri A<sup>W</sup>  12879 strain, a variant strain restricted to Mexicanl lime (Jalan et al., 2013).
=== Phenotypes ===

All //xopAG//-containing strains of //X. citri// pv. //citri// induced the hypersensitive response (HR) on grapefruit (//Citrus paradisi//) and sweet orange (//C. sinensis//) but express canker symptoms on Key lime (Escalon //et al.//, 2013). After infiltration of grapefruit leaves with inoculum adjusted to 5×10<sup>8</sup>  cfu/mL, internal bacterial populations of Xcc-A (strain A 40) and Xcc-A<sup>w</sup>  (strain 12879) were similar through the second day, but populations of Xcc-A were significantly greater than those of Xcc-A<sup>w</sup>  after six days. The symptoms caused by the Xac-A<sup>w</sup>  ΔavrGf1 strain that was mutated on avrGf1 were more similar to those produced by the wild-type Xac-A strain than to those produced by the wild-type Xac-A<sup>w</sup>  strain (Rybak //et al.//, 2009). So the whole pathogenicity was not restored.
=== Localization ===

AvrGf1 (Figueiredo //et al.//, 2011) and AvrGf2 (Gochez //et al.//, 2017) possess a N-terminal chloroplast localization signal. The signal is not shared by all members of the XopAG effector family (Gochez //et al.//, 2017). Transient expression of the protein with the first 116 amino acids deleted in grapefruit leaves resulted in the elimination of the HR and a lack of accumulation of the protein in the chloroplast.
=== Enzymatic function ===

AvrGf2 elicited rapid cell death in grapfruit leaves (Gonchez //et al.//, 2015), detailed enzymatic function has not been determined yet.
=== Interaction partners ===

The XopAG AvrGf2 effector contains a Cyp-binding site that is essential for the elicitation of HR in citrus (Gochez //et al.//, 2017). Yeast two-hybrid experiments showed strong interaction of AvrGf2 with grapefruit cyclophilin (GfCyp), whereas mutation of the GPLL motif in the cyclophilin-binding domain abolished the interaction.
===== Conservation =====

=== In xanthomonads ===

Yes (//e.g.//, //X. campestris//, //X. vasicola//) (Gochez //et al//., 2017).
=== In other plant pathogens/symbionts ===

Yes (//e.g.//, //P. syringae.// pv. //phaseolicola// (HopG1), //P. syringae// pv. //tomato// (HopG1), //Ralstonia solanacearum//, //Acidovorax citrulli//) (Gochez //et al//., 2017).
===== References =====

Escalon A, Javegny S, Vernière C, Noël LD, Vital K, Poussier S, Hajri A, Boureau T, Pruvost O, Arlat M, Gagnevin L (2013). Variations in type III effector repertoires, pathological phenotypes and host range of //Xanthomonas citri// pv. //citri// pathotypes. Mol. Plant Pathol. 14: 483-496. DOI: [[https://doi.org/10.1111/mpp.12019|10.1111/mpp.12019]]

Figueiredo JF, Romer P, Lahaye T, Graham JH, White FF, Jones JB (2011). //Agrobacterium//-mediated transient expression in citrus leaves: a rapid tool for gene expression and functional gene assay. Plant Cell Rep. 30: 1339-1345. DOI: [[https://doi.org/10.1007/s00299-011-1045-7|10.1007/s00299-011-1045-7]]
 <font 10.5pt/inherit;;#1c1d1e;;white>Gochez AM, Minsavage GV, Potnis N, Canteros BI, Stall RE, Jones JB (2015). A functional XopAG homologue in //Xanthomonas fuscans// pv.// aurantifolii //strain C limits host range. Plant Pathol, 64: 1207-1214. DOI:</font>   [[https://doi.org/10.1111/ppa.12361|10.1111/ppa.12361]]

Gochez AM, Shantharaj D, Potnis N, Zhou X, Minsavage GV, White FF, Wang N, Hurlbert JC, Jones JB (2017). Molecular characterization of XopAG effector AvrGf2 from //Xanthomonas fuscans// ssp. //aurantifolii// in grapefruit. Mol. Plant Pathol. 18: 405-419. DOI: [[https://doi.org/10.1111/mpp.12408|10.1111/mpp.12408]]

Jalan N, Kumar D, Andrade MO, Yu F, Jones JB, Graham JH, White FF, Setubal JC, Wang N (2013). Comparative genomic and transcriptome analyses of pathotypes of //Xanthomonas citri //subsp. //citri// provide insights into mechanisms of bacterial virulence and host range. BMC Genomics 14: 551. DOI: [[https://doi.org/10.1186/1471-2164-14-551|10.1186/1471-2164-14-551]]

Rybak M, Minsavage GV, Stall RE, Jones JB (2009). Identification of //Xanthomonas citri// ssp. //citri// host specificity genes in a heterologous expression host. Mol. Plant Pathol. 10: 249-262. DOI: [[https://doi.org/10.1111/j.1364-3703.2008.00528.x|10.1111/j.1364-3703.2008.00528.x]]

===== Acknowledgements =====

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