Identification of a novel type III secreted effector in Xanthomonas campestris pv. campestris

Abstract:

[Objective] To identify a novel type III secreted effector (T3SE) gene in the genome of Xanthomonas campestris pv. campestris (Xcc) strain 8004. [Methods] A Tn5 transposon system integrated with AvrBs1_59-445was constructed for library screening. The mutant library was generated based on avrBs1-deleted mutant and then screened on Capsicum annuum cv. ECW-10R. [Results] Seven clones with visible hypersensitive response (HR) were screened out via large-scale HR assay. In addition to 3 mutants inserted into known T3SE genes, a new locus was identified, which was located between XC_0438 and XC_0439 and un-annotated in Xcc 8004 by plasmid rescue and sequencing. We annotated the new gene designated as XC_0438a according to the bioinformatics analysis results. The translocation assay confirmed that the signal region of XC_0438a could guide the secretion and translocation of the reporter protein AvrBs1 and elicit the HR of ECW-10R. The results of β-glucuronidase (GUS) activity assay demonstrated that the expression of XC_0438a was induced in nutrition sterile medium and activated by the key regulatory proteins HrpG and HrpX. However, in our tested conditions, XC_0438a had no significant contribution to the pathogenesis of Xcc. [Conclusion] In summary, we identified a novel effector gene XC_0438a dependent on the type III secretion system.