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The Type III Effector XopAK

Author: Vittoria Catara
Internal reviewer: Ralf Koebnik
Expert reviewer: Guido Sessa, Xinhua Ding

Class: XopAK
Family: XopAK
Prototype: XCV3786 (Xanthomonas euvesicatoria pv. euvesicatoria, ex Xanthomonas campestris pv. vesicatoria; strain 85-10)
GenBank ID: CAJ25517.1 (485 aa)
RefSeq ID: WP_269466020.1 (262 aa)
3D structure: Unknown

Biological function

XopAK can bind the OsMYBxoc1 promoter and inhibit its transcription to remove the restriction of iron ions in rice, thereby improving the virulence of the rice pathogen Xanthomonas oryzae pv. oryzicola (Xoc) (Zhang et al., 2024).

How discovered?

XopAK was discovered using a machine-learning approach (Teper et al., 2016).

(Experimental) evidence for being a T3E

XopAK, fused to the AvrBs2 reporter, was shown to translocate into plant cells in an hrpF-dependent manner (Teper et al., 2016).




Disease severity, ion leakage, chlorophyll content of pepper plants inoculated with a mutant strain obtained by insertion mutagenesis of xopAK and in planta bacterial growth were not affected as compared to plants inoculated with the parent strain X. euvesicatoria pv. euvesicatoria (Xcv) 85-10 (Teper et al., 2016).


Upon Agrobacterium-mediated transient expression, a XopAK-GFP fusion was found to localize to the cell membrane and the nucleus of Nicotiana benthamiana cells (Zhang et al., 2024).

Enzymatic function

XopAK has been predicted to be a deaminase (Teper et al., 2016).

Interaction partners

XopAK binds to the OsMYBxoc1 promoter and inhibits its transcription (Zhang et al., 2024).


In xanthomonads

Yes (e.g., X. citri, X. euvesicatoria, X. oryzae, X. translucens) (Barak et al., 2016; Teper et al., 2016; Zhang et al., 2024)

In other plant pathogens/symbionts

Yes (e.g., Pseudomonas syringae effector HopK1, Ralstonia solanacearum (Petnicki-Ocwieja et al., 2002; He et al., 2004; Li et al., 2014; Schechter et al., 2004; Teper et al., 2016)


Barak JD, Vancheva T, Lefeuvre P, Jones JB, Timilsina S, Minsavage GV, Vallad GE, Koebnik R (2016). Whole-genome sequences of Xanthomonas euvesicatoria strains clarify taxonomy and reveal a stepwise erosion of type 3 effectors. Front. Plant Sci. 7: 1805. DOI: 10.3389/fpls.2016.01805

He P, Chintamanani S, Chen Z, Zhu L, Kunkel BN, Alfano JR, Tang X, Zhou JM (2004). Activation of a COI1-dependent pathway in Arabidopsis by Pseudomonas syringae type III effectors and coronatine. Plant J. 37: 589-602. DOI: 10.1111/j.1365-313x.2003.01986.x

Li G, Froehlich JE, Elowsky C, Msanne J, Ostosh AC, Zhang C, Awada T, Alfano JR (2014). Distinct Pseudomonas type-III effectors use a cleavable transit peptide to target chloroplasts. Plant J. 77: 310-321. DOI: 10.1111/tpj.12396

Petnicki-Ocwieja T, Schneider DJ, Tam VC, Chancey ST, Shan L, Jamir Y, Schechter LM, Janes MD, Buell CR, Tang X, Collmer A, Alfano JR (2002). Genomewide identification of proteins secreted by the Hrp type III protein secretion system of Pseudomonas syringae pv. tomato DC3000. Proc. Natl. Acad. Sci. USA 99: 7652-7657. DOI: 10.1073/pnas.112183899

Schechter LM, Roberts KA, Jamir Y, Alfano JR, Collmer A (2004). Pseudomonas syringae type III secretion system targeting signals and novel effectors studied with a Cya translocation reporter. J. Bacteriol. 186: 543-555. DOI: 10.1128/jb.186.2.543-555.2004

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: 10.1111/mpp.12288

Zhang HM, Sun BL, Wu W, Li Y, Yin ZY, Lu CC, Zhao HP, Kong LG, Ding XH (2024). The MYB transcription factor OsMYBxoc1 regulates resistance to Xoc by directly repressing transcription of the iron transport gene OsNRAMP5 in rice. Plant Commun. 5: 100859. DOI: 10.1016/j.xplc.2024.100859

bacteria/t3e/xopak.txt · Last modified: 2024/05/29 16:59 by rkoebnik