Abstract:

【Objective】 The purpose of this study was to clone and identify a pathogenicity gene of Pantoea agglomerans causing bacterial dry stalk rot on maize.【Method】 A transposon mutant library was constructed in P. agglomerans by Tn5 transposon mutagenesis. The mutants with defective pathogenicity were screened using the stalk-injecting inoculation on the susceptible maize inbred line PS056. One mutant lost pathogenicity was obtained and designated as PA121.【Result】Southern blotting analysis indicated that the mutant PA121 had a single-copy Tn5 transposon which inserted into the yhfK at the site of 1 082 bp upstream. The yhfK encodes a conserved inner membrane protein, identified by bi-directional sequencing based on Tn5 sequence. Phenotypic analysis indicated a complementary plasmid retained the pathogenicity on host PS056. The activities of extracellular enzymes, such as protease, amylase and cellulase, were not affected in mutant PA121. RT-PCR analysis demonstrated that the yhfK regulated the transcription of hrpA.【Conclusion】This study demonstrates that the yhfK affects pathogenicity of P. agglomerans, which is a critical element in the pathogenesis of P. agglomerans causing bacterial dry stalk rot on maize.

Key words: Pantoea agglomerans, Tn5 transposon, maize, bacterial dry stalk rot, yhfK