| Bacterial blight of rice,an important bacterial disease caused by Xanthomonas oryzae,can seriously reduce rice production.Traditional antibiotic measures caused severe antibiotic resistance in pathogenic bacteria.A new approach screening compounds which target the virulence factors rather than killing the bacterial pathogens is necessary.The type III secretion system(T3SS),a key virulence factor and highly conserved in many gram-negative bacteria,was regarded as such an ideal target.In this study,345 compounds including plant natural products,synthetic compounds,and marine microbial extracts were screened,using T3SS as a target,by a high-throughput screening system.The functional mechanism of CZ-1、CZ-4 and CZ-9,III-2、III-3、III-4、III-12 and III-14,WS-C-1、WS-C-17、WS-C-22 and WS-C-24 without killing the bacteria was evaluated.we analyzed their effects on the hypersensitive response(HR)in non-host tobaccoleaves induced by Xoo strain PXO99~A.Pre-treatment of PXO99~A with CZ-1、CZ-4、CZ-9、III-2、III-3 and III-4 resulted in significantly attenuated HR without killing bacterial cells,suggesting that the inhibitors effectively suppressed the function of the T3SS of PXO99~A but not the its growth.The effects on T3SS gene transcription and effector translocation were examined by the qRT-PCR and RNA-seq sequencing,some represent were reduced by the treatment of inhibitors.and the control effects on rice seedlings and adults were performed.The results demonstrated that the compounds could inhibit the expression of the T3SS in Xoo through the HrpG-HrpX regulatory cascade.In vivo bioassay results showed that the compounds could reduce the symptom in rice caused by Xoo.These findings provided potential anti-virulence lead compounds which might be used in agricultural production in the future. |
