title: Activated and inactivated immune responses in Caenorhabditis elegans against Photorhabdus luminescens TT01.
abstract: The Gram-negative bacterium Photorhabdus luminescens which symbiotically associates with the entomopathogenic nematode Heterorhabditis bacteriophora, has a broad insecticidal and nematicidal activity. The virulence of P. luminescens toward the non-mutualistic nematode Caenorhabditis elegans has not been described. We showed that when fed on P. luminescens, the intestinal cells of C. elegans worms become delicate and some crystal-like structure was developed within the intestinal lumen. Next, we examined the requirement of the p38 mitogen-activated protein kinase (MAPK) and insulin/IGF-1 signaling pathway against P. luminescens. Depletion of pmk-1 by RNAi enhances susceptibility to P. luminescens, and numerous downstream targets regulated by the p38 MAPK pathway were induced when fed on P. luminescens. On the other hand, knockdown of daf-16 has no effects on C. elegans lifespan, but knockdown of daf-2 dramatically increased resistance to P. luminescens in a daf-16-dependent manner. We also revealed one of the daf-2 ligands ins-7 was induced and ins-7 deletion mutant survived longer when fed on P. luminescens. These results suggest the p38 MAPK pathway is activated and required for the host defense against P. luminescens. Insulin/IGF-1 signaling pathway is inactivated by P. luminescens through the overexpression of insulin-like gene.
authors.affiliation: Laboratory of Nematology, Department of Applied Biological Sciences, Saga University, Saga, 840-8502 Japan ; Laboratory of Terrestrial Microbial Ecology, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto, 606-8502 Japan ; The United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima, 890-8580 Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Sato
authors.affiliation: Laboratory of Nematology, Department of Applied Biological Sciences, Saga University, Saga, 840-8502 Japan ; Laboratory of Terrestrial Microbial Ecology, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto, 606-8502 Japan.
authors.forename: Toyoshi
authors.initials: T
authors.lastname: Yoshiga
authors.affiliation: Department of Environmental Biology, College of Bioscience & Biotechnology, Chubu University, 1200 Matsumoto, Kasugai, 487-8501 Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Hasegawa
keywords: Caenorhabditis elegans; Entomopathogenic nematode; Heterorhabditis bacteriophora; Insulin/IGF-1; Pathogenicity; Photorhabdus luminescens