Research On The Virulence Mechanism Of Type ? Secretory System In Rice Bacterial Brown Stripe Pathogen Acidovorax Avenae Subsp.Avenae RS-2

Bacterial brown stripe is a serious disease in rice that is caused by the gram-negative bacteria Acidovorax avenae subsp.avenae(Aaa).This disease is widely distributed in rice-planting area throughout the world.In recent years,rice bacterial brown stripe has been often reported in China.Furthermore,our previous studies have revealed the importance of Type VI secretion system(T6SS)in virulence of Aaa strain RS-1.Howerver,strain RS-2 demonstrated weak virulence compared to the virulent strain RS-1 although both of them have same genes of T6SS.Therefore,it is very necessary to understand the role of T6SS in the virulent mechanism of Aaa.This study compared the virulence-related phenotypes between the wild type and 25 T6SS mutants of Aaa strain RS-2,which were constructed using the method of homologous recombination.The results showed that mutation of pppA,clpB,hcp,dotU,icmF,impJ,impM,vgrG-1,vgrG-2,vgrG-3,vgrG-4,vgrG-5,vgrG-6,vgrG-7 and vgrG-8 genes resulted in a significant 17.47?56.4%decrease in the virulence,and 37.78?68.46%decrease in the secretion of Hcp protein.After incubation 12 h,all 25 T6SS mutants caused a significant decrease in OD600.Mutation of pppA,clpB,icmF,impJ and impM caused a 38.3?56.4%decrease in the biofilm formation of strain RS-2,while mutation of clpB,icmF and hcp resulted in a 44.00?46.80%reduction in the motility of strain RS-2.No significant difference were observed in these virulence-related phenotypes between the other muants and the wild type.However,there was no differences in these virulence-related phenotypes between the wild type and the constructed complemented strains for the T6SS mutants pppA,clpB,hcp,dotU,icmF,impJ and impM,which casued the most significant reduction in virulcen of Aaa strain RS-2.This study demonstrated the importance of T6SS genes in particular pppA,clpB,hcp,dotU,icmF,impJ,inipM and 8 vgrG genes in virulence of Aaa strain RS-2.Furthermore,mutation of these virulence-related genes casued a significant reduction in the secretion of Hcp protein,highlighting that these T6SS genes may function by reducing the secretion of Hcp protein.Furthermore,pppA,clpB,icmF,impJ and impM genes affected the biofilm formation,while clpB,hcp and icmF genes affected the motility of Aaa strain RS-2,revealing that pppA,clpB,hcp,dotU,icmF,impJ and impM genes may have an impact on the virulence of Aaa by changing the other phenotypes.However,this study clearly revealed the importance and diversity of T6SS genes function in the virulence mechanism of Aaa,which provide a basis for fully understanding the the virulent mechanism of Aaa.