A human pathogenic bacteriumShigellaproliferates in the plant through the adoption of type III effectors for Shigellosis

Abstract

24Human enteropathogenic bacteria has been reported to be transmitted by fresh vegitables. Shigella, which 25 infects primates, is reportedly transmitted by fresh vegetables; however, its molecular interactions with 26 plants have not been elucidated. Here, we show that four Shigella strains, S. boydii (S. b), S. sonnei, S. 27 flexneri 2a (S. f 2a), and S. flexneri 5a (S. f 5a), proliferated at different levels in Arabidopsis thaliana. 28 Microscopic studies revealed that these bacteria were present inside leaves and damaged plant cells. Green 29 fluorescent protein (GFP)-tagged S. b and S. f 5a colonized in leaves only, and S. f 2a colonized both leaves 30 and roots. Using mutants lacking type III secretion systems (T3SS), we found that T3SS of Shigella that 31 regulate the pathogenesis of Shigellosis in humans also play a central role in proliferation in Arabidopsis. 32 Strikingly, the immunosuppressive activity of two T3S effectors, OspF and OspG, were needed for the 33 proliferation of Shigella in Arabidopsis. Of note, delivery of OspF or OspG effectors inside of plant cells 34 upon Shigella inoculation was confirmed by using a split GFP system, respectively. These findings 35 demonstrate that the human pathogen Shigella can proliferate in plants by adoption of immunosuppressive 36 machinery for its original host human. 37 38 effectors 41 42 43 65 number of infections might be higher because mild symptoms are not reported (Mortality and Causes of 66 Death, 2016), suggesting that the microorganism may employ a variety of survival strategies not only for 67 human intestinal infection but also for survival in a non-adapted host. Although Shigella contamination has 68 4also been reported in plants (Naimi et al., 2003; Ohadi et al., 2013), it is not yet known whether the 69 bacterium actively invades and/or proliferates inside the plant. 70Unlike animals, plants have no adaptive immune system; instead, each cell possesses an innate 71 immune system. The innate immune system in plants and animals recognizes and suppresses pathogens and 72 has common features that are preserved throughout evolution. Plant pattern recognition receptors recognize 73 conserved microbial or pathogen-associated molecular patterns; the pattern-triggered immunity (PTI) is 74 activated via the mitogen-activated protein kinase (MAPK) cascades (Jones and Dangl, 2006). To suppress 75 PTI, bacteria inject effector proteins into plant cells using type III secretion systems (T3SS). To counteract 76 this PTI evasion response, the plant nucleotide binding-leucine rich repeat proteins recognize the pathogen 77 effectors; effector-triggered immunity is then activated to accompany the hypersensitive response (Jones and 78 Dangl, 2006). For human or animal intestinal bacteria to infect plants, the PTI must first be disabled. S. 79 enterica serovar Typhimurium, similar to its activity in the mammalian host, uses T3SS to suppress plant 80 immune responses (Schikora et al., 2011; Schikora et al., 2012). In particular, one of the T3S effector 81 p...