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Author: Ralf Koebnik
Expert reviewer: WANTED!

Class: XopBB
Family: XopBB
Prototype: ELAGFFLI_02299 (Xanthomonas hortorum pv. pelargonii; strain 305)

GenBank ID: CAD0333498 (332 aa)
RefSeq ID: WP_251761698.1 (220 aa, corresponding to the C-terminal domain)
3D structure:

Biological function

How discovered?

XopBB was discovered using a machine-learning approach for the prediction of T3Es (Wagner et al., 2022, 2023).

(Experimental) evidence for being a T3E

To examine the translocation of the predicted T3E, a reporter system based on the delivery of a truncated form of the Xanthomonas euvesicatoria T3E AvrBs2 (amino acids 62–574) into susceptible plant cells was utilized. AvrBs262–574 lacks the type 3 translocation signal, but is sufficient to elicit a hypersensitive response (HR) in plants expressing the Bs2 resistance gene. A fusion of the XopBB ORF, including 24 bp upstream of its ATG start codon, with AvrBs262–574 elicited HR response in the pepper line ECW20R, which encodes a functional Bs2 resistance gene (Wagner et al., 2023).


The xopBB gene contains a perfect PIP box in its promoter region and is likely co-regulated with the T3SS under control of HrpG and HrpX (Wagner et al., 2023).





Enzymatic function


Interaction partners



In xanthomonads

Yes, X. arboricola and X. hydrangeae (Wagner et al., 2023).

In other plant pathogens/symbionts

Yes, in species of Acidovorax (e.g. A. avenae, A. citrulli, A. oryzae) (Wagner et al., 2023). XopBB is distantly related to HopF2 (syn. AvrPphF) from the Pseudomonas syringae species complex, e.g. P. amygdali, P. cannabina (ca. 30 % amino acid sequence identity).


Wagner N, Avram O, Gold-Binshtok D, Zerah B, Teper D, Pupko T (2022). Effectidor: an automated machine-learning-based web server for the prediction of type-III secretion system effectors. Bioinformatics 38: 2341-2343. DOI: 10.1093/bioinformatics/btac087

Wagner N, Ben-Meir D, Teper D, Pupko T (2023). Complete genome sequence of an Israeli isolate of Xanthomonas hortorum pv. pelargonii strain 305 and novel type III effectors identified in Xanthomonas. Front. Plant Sci. 14: 1155341. DOI: 10.3389/fpls.2023.1155341

bacteria/t3e/xopbb.txt · Last modified: 2023/12/18 15:23 by rkoebnik