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Molecular Diagnosis and Diversity for Regulated Xanthomonas
Bacterial virulence factors
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Author: Laurent D. Noël
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Class: XopAC
Family: XopAC
Prototype: XopAC (Xanthomonas campestris pv. campestris strain 8004)
RefSeq ID: AFP74845.1 (536 aa)
3D structure: unknown
XopAC/AvrAC was identified as a putative type III effector because of the presence of seven prokaryotic-type leucine-rich repeats in its C-terminal domain and a PIP-box motif in xopAC promoter suggestive of a hrpX-dependent expression (Xu et al., 2008).
The first XopAC1-167 can mediate secretion and translocation of AvrBs159-445P in pepper leaves in a hrpF-dependent manner (Xu et al., 2008).
xopAC promoters possess a PIP-box motif (Xu et al., 2008). Expression of xopAC is induced in hrp-inducing medium XVM2 in a hrpG- and hrpX-dependent manner (Xu et al., 2008).
xopAC, also named avrAC, confers avirulence to Xanthomonas campestris pv. campestris on Arabidopsis accession Col-0 but not Kas (Xu et al., 2008). xopAC avirulence is weak in mesophyll tissue but strong upon inoculation of hydathodes or vascular tissues (Xu et al., 2008; Cerutti et al., 2017). When heterologously expressed in virulent Ralstonia solanacearum or Pseudomonas syringae pv. tomato, it also confers avirulence on Arabidopsis accession Col-0 (Guy et al., 2013b). xopAC contributes to Xanthomonas campestris pv. campestris pathogenicity on Brassica oleracea and Arabidopsis in a BIK1-dependent manner (Feng et al., 2012). XopAC inhibits BIK1 kinase activity and blocks flg22-induced PTI responses (Feng et al., 2012). Transgenic expression of xopAC in Arabidopsis accession Col-0 induces early growth arrest at both apical and root meristems (Wang et al., 2015).
XopAC was localized to the plasma membrane upon Agrobacterium-mediated transient expression in Nicotiana benthamiana (Guy et al., 2013b). This localization is dependent on its LRR domain suggesting that XopAC localization is dependent on its interacting partners (Guy et al., 2013b).
XopAC presents an uridylyl transferase activity dependent on residue H469 (Feng et al., 2012). XopAC is able to uridylylate both conserved S236 and T237 in BIK1. Similar activity was demonstrated for all other RLCK VIIa tested including PBL2 (Feng et al., 2012; Wang et al., 2015).
Nine Arabidopsis RLCKs (Receptor-like cytoplasmic kinases, subfamily VIIa) were described as putative interactors of XopAC using yeast-two hybrid (Guy et al., 2013b). Importantly, PBL2 RLCK is essential for XopAC avirulence function and BIK1 RLCK for XopAC virulence functions (Guy et al., 2013b; Feng et al., 2012; Wang et al., 2015).
xopAC is present in many Xanthomonas campestris pv. campestris strains as well as several Xanthomonas campestris pv. raphani (Guy et al., 2013a). To date, all allelic variants of XopAC conferred avirulence in Arabidopsis accession Col-0 (Guy et al., 2013b).
No.
Cerutti A, Jauneau A, Auriac M-C, Lauber E, Martinez Y, Chiarenza S, Leonhardt N, Berthomé R, Noël LD (2017). Immunity at cauliflower hydathodes controls infection by Xanthomonas campestris pv. campestris. Plant Physiol. 174: 700-712. DOI: 10.1104/pp.16.01852
Feng F, Yang F, Rong W, Wu X, Zhang J, Chen S, He C, Zhou JM (2012). A Xanthomonas uridine 5'-monophosphate transferase inhibits plant immune kinases. Nature 485: 114-118. DOI: 10.1038/nature10962
Guy E, Genissel A, Hajri A, Chabannes M, David P, Carrère S, Lautier M, Roux B, Boureau T, Arlat M, Poussier S, Noël LD (2013a). Natural genetic variation of Xanthomonas campestris pv. campestris pathogenicity on Arabidopsis revealed by association and reverse genetics. MBio 4: e00538-12. DOI: 10.1128/mBio.00538-12
Guy E, Lautier M, Chabannes M, Roux B, Lauber E, Arlat M, Noël LD (2013b). xopAC-triggered immunity against Xanthomonas depends on Arabidopsis receptor-like cytoplasmic kinase genes PBL2 and RIPK. PLoS One 8: e73469. DOI: 10.1371/journal.pone.0073469
Wang G, Roux B, Feng F, Guy E, Li L, Li N, Zhang X, Lautier M, Jardinaud MF, Chabannes M, Arlat M, Chen S, He C, Noël LD, J.M. Zhou JM (2015). The decoy substrate of a pathogen effector and a pseudokinase specify pathogen-induced modified-self recognition and immunity in plants. Cell Host Microbe 18: 285-295. DOI: 10.1016/j.chom.2015.08.004
Xu RQ, Blanvillain S, Feng JX, Jiang BL, Li XZ, Wei HY, Kroj T, Lauber E, Roby D, Chen B, He YQ, Lu GT, Tang DJ, Vasse J, Arlat M, Tang JL (2008). AvrACXcc8004, a type III effector with a leucine-rich repeat domain from Xanthomonas campestris pathovar campestris confers avirulence in vascular tissues of Arabidopsis thaliana ecotype Col-0. J. Bacteriol. 190: 343-355. DOI: 10.1128/JB.00978-07
