Analysis of the pilN gene in Acidovorax citrulli

To investigate functions of fimbrial assembly family gene in Acidovorax citrulli(Ac),we generated a transposon(Tn5)mutant library on the background of strain xjl12 and screened it for reduced virulence by seed-transmission assays and injection inoculation with melons.The gene insertional mutant ΔpilNac was generated by biparental mating from the wild-type strain xjl12,meanwhile cell morphology,motility and pathogenicity in host and hypersensitive response(HR)in nonhost tobacco were determined.Here,we got one strain Δxj-7 with reduced virulence.This Tn5 mutant was impaired in pilN,which was involved in fimbrial assembly family protein and played a part in the biosynthesis of type Ⅳ pili.The pathogenicity on seed leaf was obviously attenuated in ΔpilNac compared to wild type.There was significant difference in bacterial growth in MMX medium,production of cellulose and induction of HR between mutant(ΔpilNac)and wild type.In addition,these results of qRT-PCR demonstrated that the transcription level of hrpG,hrcV and celA were down-regulated in ΔpilNac.The complementation strain restored the phenotypes of pilN gene partially or completely.This study showed that the ΔpilNac mutation had influence not only in growth,but also in pathogenicity in Ac.