Regular research paper A human pathogenic bacterium Shigella proliferates in the plant through the adoption of type III effectors for Shigellosis

Abstract Human intestinal pathogenic bacteria has been reported to be transmitted by fresh vegitables. Shigella, which infects primates, is reportedly transmitted by fresh vegetables; however, its molecular interactions with plants have not been ellucidated. Here, we show that four Shigella strains, S. boydii (S. b), S. sonnei (S. s), S. flexneri 2a (S. f 2a), and S. flexneri 5a (S. f 5a), proliferated at different levels in Arabidopsis thaliana. Microscopic studies revealed that these bacteria were present inside leaves and damaged plant cells. GFP-labeled S. b, S. f 2a, and S. f 5a entered plants via guard cells, and S. f 2a infiltrated root tissues and colonized roots. Using mutants lacking type III secretion systems (T3SS), we found that T3SS of Shigella that regulate the pathogenesis of shigellosis in humans also play a central role in attachment and multiplication in Arabidopsis. Furthermore, the immunosuppressive activity of two T3S effectors, OspF and OspG, were needed for the proliferation of Shigella in Arabidopsis. Of note, delivery of OspF or OspG effectors inside of plant cells upon Shigella inoculation was confirmed by using a split GFP system, respectively. These findings demonstrate that the human pathogen Shigella can proliferate in plants by adoption of immunosuppressive machinery for its original host human.