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Author: Jose Gadea
Class:XopAQ
Family:XopAQ
Prototype: XopAQ (X. gardneri (Xg) strain 101 (ATCC 19865).
GenBank ID: EGD19295.1 (95 aa)
3D structure: Unknown
Biological function
How discovered? XopAQ was discovered by sequencing the genome of the X. gardneri (Xg) strain 101 (8).
(Experimental) evidence for being a T3E: A functional screen to isolate Ralstonia solanacearum genes encoding proteins translocated into plant cells reveal that the gene Rip6 and Rip11 were two new translocated proteins. XopAQ is 60% identical at the protein level to these two proteins. BlastP alignment between XopAQ and Rip6 indicates that the homology is spanned along the whole protein, including the N-terminal part, suggesting that the functional motif that drives translocation in Rip6 is conserved in XopAQ. Translocation assays using a strain deleted in the hpaB gene of Ralstonia indicates that Rip6 and Rip11 requires HpaB for their effective translocation into plant cells via the Hrp T3SS (12). However, no functional translocation assay has been performed for Xanthomonas XopAQ effector to our knowledge.
Regulation: XopAQ is up-regulated when X.citri pv. citri 306 and X.citri pv. citri Aw12879 (restricted to Mexican lime) are grown in XVM2 medium, known to induce hrp gene expression, as compared with nutrient broth (NB). However, no differential expression was observed in this gene among these two strains. (9).
The X. arboricola gene shows a putative plant-inducible promoter box (PIP-BOX) sequence, 67 bp upstream of the TATA box (13).
Phenotypes:Unknown
Localization: CSS-Palm suite reveals potential myristoylation/palmitoylation motifs for XopAQ, suggesting that the protein could be targeted to the cytoplasmic membrane (11). This targeting is facilitated by a simple sequence motif at the N terminus of the polypeptide chain.
Enzymatic function: Unknown. No known motifs are found in the Rip6 and Rip11 proteins of Ralstonia (12). No motifs are found in the X. gardneri protein neither (Prosite analysis).
Interaction partners:Unknown
Conservation
In xanthomonads: Yes. Widely present in the most agressive citrus canker-causing X.citri A strains but also in the AW strain (narrow host range) (1,5), and also in the milder X. fuscans B strain, but not in the X. fuscans C strain (restricted to C. aurantifoli). (2). Present in Xanthomonas gardneri but not in some strains of X. perforans nor X. euvesicatoria strains affecting pepper and tomato (3, 8, 10). Two paralogs of XopAQ present in Strains 66b and LMG 918 of X. euvesicatoria, but not present in other LMG strains, 83b, 85-10, or X. euvesicatoria pv. rosa (11). Present in pathogenic (but not in non-pathogenic) X. arboricola pv. pruni (5, 7), but not in the related X. juglandis or X. corylina (6) Also present in X. citri pv. viticola (3) and other X, citri pathovars (blastp analysis). X. phaseolis and X. populi, among others, present a protein with moderate homology in a blastp analysis.
In other plant pathogens/symbionts:Yes (Ralstonia).
References