Author: Laurent Noël
Reviewer: Ralf Koebnik

Class: XopJ
Family: XopJ6
Prototype: XopJ6 (Xanthomonas campestris pv. campestris; strain CN06)
RefSeq ID: WP_196765268.1 (471 aa)
3D structure: Unknown

XopJ6 was initially identified in Xanthomonas campestris pv. campestris as a homolog of Ralstonia pseudosolanacearum , the presence of which correlated with induction of an hypersensitive response (HR) on Brassacia oleracea cv. clovis F1 (Lauber et al., 2024).

• XopJ6 is a homolog of PopP2, with 35% overall sequence identity with a good conservation of the acetyltransferase domain (Lauber et al., 2024).
• xopJ6 induces HR on cauliflower in a type III secretion-dependent-manner (Lauber et al., 2024).
• In Arabidopsis, XopJ6 effector-triggered immunity (ETI) is mediated by two nuclear proteins RRS1 and RPS4 (Lauber et al., 2024).
• No direct experimental demonstration for translocation.

xopJ6 is present on a ca. 9-kb transposable element named Tn6714. It was found in multiple identical copies, likely due to recent transposition events (Lauber et al., 2024). Many Xanthomonas campestris pv. campestris strains do not contain any xopJ6 gene and are still potent and adapted pathogenic strains (Lauber et al., 2024).

xopJ6 promoters possess a PIP-box motif (Lauber et al., 2024). Expression of xopJ6 is induced in the hrp-inducing medium MME or by the hrpG* gain-of-function allele of hrpG in a hrpG- and hrpX-dependent manner (Lauber et al., 2024). Copy number variation of xopJ6 results in variable levels of transcription.

• xopJ6 induces an hypersensitive response and ETI on the cauliflower (Brassica oleracea) cv. Clovis F1 (Lauber et al., 2024).
• xopJ6 induces ETI in Arabidopsis thaliana in an RRS1-R- and RPS4-dependent manner (Lauber et al., 2024).
• xopJ6 delivered by Pseudomonas fluorescens Pfo-1 induces HR in Arabidopsis thaliana in an RRS1-R-, EDS1- and RPS4-dependent manner (Lauber et al., 2024).
• xopJ6 is able to dampen flg22-induced PTI responses in Nicotiana benthamiana (Lauber et al., 2024).
• xopJ6 quantitatively contributes to Xanthomonas campestris pv. campestris pathogenicity in susceptible accessions Col-0 and Sf-2 of Arabidopsis: xopJ6 mutants are less virulent while those overexpressing xopJ6 are more virulent (Lauber et al., 2024).

XopJ6-CFP has a nucleo-cytoplasmic localization upon Agrobacterium-mediated expression in N. benthamiana (Lauber et al., 2024).

Recombinant XopJ6 purified from E. coli encodes an acetyl transferase able to acetylate Arabidopsis WRKY22 (Lauber et al., 2024).

• XopJ6 interacts with RRS1-R WRKY domain in yeast two-hybrid experiments (Lauber et al., 2024).
• XopJ6 interacts with Arabidopdis RRS1-R resistance protein and WRKY22 transcription factor (Lauber et al., 2024).
• A single AA substituion (N382K) abolishes interaction with Arabidopsis WRKY22 and RRS1-R and is required for ETI in Arabidopsis and cauliflower (Lauber et al., 2024).
• WT XopJ6 and XopJ6^N382K both suppress Flg22 ROS burst in a WRKY-independent manner (Lauber et al., 2024).

By 2024, xopJ6 has only been detected in Xanthomonas campestris pv. campestris (Lauber et al., 2024) and in Xanthomonas translucens pv. graminis.

XopJ6 is a homolog of the type III effector PopP2 from Rastonia pseudosolanacearum. Homologs are also present in strains of Collimonas and Duganella.

Lauber E, González-Fuente M, Escouboué M, Vicédo C, Luneau JS, Pouzet C, Jauneau A, Gris C, Zhang ZM, Pichereaux C, Carrère S, Deslandes L, Noël LD (2024). Bacterial host adaptation through sequence and structural variations of a single type III effector gene. iScience 27: 109224. DOI: 10.1016/j.isci.2024.109224