RESUMEN
Bacteria are exposed to and tolerate diverse and potentially toxic compounds in the natural environment. While efflux transporters are generally thought to involve bacterial antibiotic resistance in vitro, their contributions to plant bacterial virulence have so far been poorly understood. Pseudomonas cannabina pv. alisalensis (Pcal) is a causal agent of bacterial blight of Brassicaceae. We here demonstrated that NU19, which is mutated in the resistance-nodulation-cell division (RND) transporter encoded gene, showed reduced virulence on cabbage compared to WT, indicating that the RND transporter contributes to Pcal virulence on cabbage. We also demonstrated that brassinin biosynthesis was induced after Pcal infection. Additionally, the RND transporter was involved in resistance to plant-derived antimicrobials and antibiotics, including the cabbage phytoalexin brassinin. These results suggest that the RND transporter extrudes plant-derived antimicrobials and contributes to Pcal virulence. We also found that the RND transporter contributes to Pcal virulence on Brassicaceae and tomato, but not on oat. These results suggest that the RND transporter contributes to Pcal virulence differentially depending on the host-plant species. Lastly, our expression-profile analysis indicated that the type-three secretion system (TTSS), which is essential for pathogenesis, is also involved in suppressing brassinin biosynthesis. Taken together, our results suggest that several Pcal virulence factors are involved in resistance to plant-derived antimicrobials and bacterial survival during infection.
RESUMEN
To date, the chimpanzee has been used as the natural infection model for hepatitis B virus (HBV). However, as this model is very costly and difficult to use because of ethical and animal welfare issues, we aimed to establish the tupaia (Tupaia belangeri) as a new model for HBV infection and characterized its intrahepatic innate immune response upon HBV infection. First, we compared the propagation of HBV genotypes A2 and C in vivo in tupaia hepatocytes. At 8-10days post infection (dpi), the level of HBV-A2 propagation in the tupaia liver was found to be higher than that of HBV-C. Abnormal architecture of liver cell cords and mitotic figures were also observed at 8 dpi with HBV-A2. Moreover, we found that HBV-A2 established chronic infection in some tupaias. We then aimed to characterize the intrahepatic innate immune response in this model. First, we infected six tupaias with HBV-A2 (strains JP1 and JP4). At 28 dpi, intrahepatic HBV-DNA and serum hepatitis B surface antigens (HBsAg) were detected in all tupaias. The levels of interferon (IFN)-ß were found to be significantly suppressed in the three tupaias infected with HBV A2_JP4, while no significant change was observed in the three infected with HBV A2_JP1. Expression of toll-like receptor (TLR) 1 was suppressed, while that of TLR3 and TLR9 were induced, in HBV A2_JP1-infected tupaias. Expression of TLR8 was induced in all tupaias. Next, we infected nine tupaias with HBV-A2 (JP1, JP2, and JP4), and characterized the infected animals after 31 weeks. Serum HBsAg levels were detected at 31 weeks post-infection (wpi) and IFN-ß was found to be significantly suppressed in all tupaias. TLR3 was not induced, except in tupaia #93 and #96. Suppression of TLR9 was observed in all tupaias, except tupaia #93. Also, we investigated the expression levels of cyclic GMP-AMP synthase, which was found to be induced in all tupaias at 28 dpi and in four tupaias at 31 wpi. Additionally, we evaluated the expression levels of sodium-taurocholate cotransporting polypeptide, which was found to be suppressed during chronic HBV infection. Thus, the tupaia infection model of HBV clearly indicated the suppression of IFN-ß at 31 wpi, which might have contributed to the establishment of chronic HBV infection.
