The Study Of Strategy Conquer Low-oxygen Tension And Mining Of Novel Type ? Effector Of Xanthomonas Oryzae Pv.oryzae PXO99~A

Bacterial leaf blight?BLB?is a destructive rice disease caused by Xanthomonas oryzae pv.oryzae?Xoo?,resulting in serious reduction of rice protuction.During the infection,Xoo not only depend on the function of various of virulence factors,but also need to overcome various environmental stresses encountered during the process of infection.It is important to study the virulence factors and the strategies to overcome environmental stresses of Xoo.Oxygen plays a critical role in host-pathogen interactions.Study have shown that local hypoxia would be induction during the infection of pathogen.Xoo will cause and suffer hypoxia in the vascular bundle of rice in the process of it invasion.Xoo is a kind of aerobic bacteria,hypoxia has an negative on its growth and proliferation.On the other hand,hypoxia could be sensed by Xoo to regulate the expression of oxygen and virulence related gene to adapt to the hypoxia and promote infection.To study the strategy of Xoo adaptation to hypoxia stress,we investigated the effects of hypoxia on the growth,metabolism and pathogenicity to Xoo PXO99 A.Total protein of PXO99 A culture under normoxic and hypoxia condition was extracted and identified.187 and 140 proteins was uniquely detected under normoxic and hypoxic conditions,respectively.The unique detected proteins could be categorised into 34 and 32 groups under normoxic and hypoxic conditions on the basis of Web Gene Ontology Annotation Plot?WEGO?,respectively.Gene Ontology?GO?enrichment analysis shows that the uniquely detected proteins under normoxic conditions is mainly related to chemotaxis and cell wall biosynthesis.However,the uniquely detected proteins under hypoxic involved in aromatic amino acid were highly enriched in Xoo.KEGG?Kyoto Encyclopedia of Genes and Genomes?pathway analysis showed that the uniquely detected proteins are involved in 33?specified?plus 31?shared?metabolic processes under hypoxic conditions while in 17?specified?plus 31?shared?under normoxic conditions.15 proteins were uniquely detected under low-oxygen tension were used to study the adaptability and pathogenicity of Xoo under hypoxic conditions.Those proteins are involved in bacterial adhesion,biosynthesis of aromatic amino acids,glycolysis,butyric acid,or propionic acid metabolism.The 15 protein coding genes were deleted by frame deletion,and 10 mutants were obtained.We found that the delation of Acetolactate synthase 2 catalytic subunit PXO₀2606 result in loss of virulence,mutants of glucokinase PXO₀0609 and F5/8 type C domain protein PXO₀1697 result in decline of pathogentic..Further study found that PXO₀2606 shows growth defect in XOM2,it is why pathogentic defenction.The function of PXO₀0609 and PXO₀1697 was further explored,and it was found that the extracellular polysaccharide?EPS?production and movement ability of PXO₀0609 deletion mutants were significantly weaker than wild-type strains.Therefore,we hypothesized that Xoo promotes the synthesis of EPS and bacterial proliferation through PXO₀0609 and contributed to its infection under hypoxia condition.The PXO₀1697 is composed of N terminal signal peptide,F5/8 type C and AfuC?Alpha-L-fucosidase?conserved domain.The AfuC domain belongs to the superfamily of fucose,which is involved in carbohydrate metabolism and transport.F5/8 type C could interacts with lipids,polysaccharides or proteins and participates in cell adhesion.Adhesion is a critical step in the host infection by pathogens.Adhesion factors may be recognized by the host and cause the host's primary immune response,PTI?PAMP-triggered immunity?.Transient expression of PXO₀1697 on tobacco leaves showed that it could cause PTI reaction in non host plants.These results show that F5/8 type C domain specifically recognises a carbohydrate moiety on the cell wall or the extracellular matrix and then guides the degradation of the active alpha-L-fucosidase domain to its target.