Reverse genetic analysis of components of the Toll signaling pathway in Caenorhabditis elegans

Background: Both animals and plants respond rapidly to pathogens by inducin g the expression of defense-related genes. Whether such an inducible system of innate immunity is present in the model nematode Caenorhabditis elegans is currently an open question. Among conserved signaling pathways importan t for innate immunity, the Toll pathway is the best characterized. In Droso phila, this pathway also has an essential developmental role. C, elegans po ssesses structural homologs of components of this pathway, and this observa tion raises the possibility that a Toll pathway might also function in nema todes to trigger defense mechanisms or to control development. Results: We have generated and characterized deletion mutants for four gene s supposed to function in a nematode Toll signaling pathway. These genes ar e tol-1, trf-1, pik-1, and ikb-1 and are homologous to the Drosophila melan ogaster Toll, dTraf pelle, and cactus genes, respectively. Of these four ge nes, only tol-l is required for nematode development, None of them are impo rtant for the resistance of C. elegans to a number of pathogens. On the oth er hand, C. elegans is capable of distinguishing different bacterial specie s and has a tendency to avoid certain pathogens, including Serratia marcesc ens, The tol-1 mutants are defective in their avoidance of pathogenic S. ma rcescens, although other chemosensory behaviors are wild type. Conclusions: In C, elegans, tol-1 is important for development and pathogen recognition, as is Toll in Drosophila, but remarkably for the latter role, it functions in the context of a behavioral mechanism that keeps worms awa y from potential danger.