The Transductional Pathway To Sense The Attractive Signal Molecule In Dole And2-ethyl Hexanol In Caenorhabditis Elegans

Caenorhabditis elegans lives in a complex environment, and feeds on the soil bacteria. However, there also exist various pathogenic microorganisms in the same enviroment. Therefore, the ability to distinguish beneficial food from the pathogenic bacteria is especially important for nematodes survival. Therefore, it has been reported that C. elegans can sense environment chemicals including volatile or water-soluble compounds mediated by the functions of chemosensation neurons, which helps the worms to combine these chemiclal signals with food or dangerous factors. Olfaction is one of the most efficient systems to sense the external environments, and subsequently produce chemotaxis and escape.Our previous research has suggested that Bacillus nematocida B16can attract and kill nematodes efficiently, and furthermore, the attraction of worms is induced by the volatile compounds from B. nematocida B16. In our current study, we screened the volatile compounds and found that indole and2-ethyl hexanol had the obvious attractive abilities for worms. Next, we identified the signal pathways that was responsible for sensing these two signal molecues.In the paper, the main results are as follows:1. The olfactory neurons in C. elegans that sensed the two attractive volatile compounds (eg. indole and2-ethyl hexanol) were determined.After testing the chemotaxis of two mutants of odr-1and odr-7. which are the lost-function mutation of AWA and AWC respectively, it was found that the sensing of indole in C. elegans was mainly mediated by the AWC olfactory sensory neunons; and the sensing of2-ethyl hexanol was mainly mediated by the AWA olfactory sensory neurons.2. STR-193in AWC neunons is the G-protein-coupled receptor (GPCR) for the chemotaxis of indole, and STR-7in AWA neurons is the GPCR for the chemotaxis of2-ethyl hexanol.At present, the olfactory signal pathway between the chemotaxis compound and its receptor has rarely described in C. elegans. The receptor ODR-10has been reported to detect diacetyl in AWA neunons. Here, our data showed that the two GPCRs STR-193and STR-7were the olfactory receptors in C. elegans. Between them, the RNAi mutants of gene str-193could not sense indole and the RNAi mutants of str-7could not sense2-ethyl hexanol. However, in the mutation of those two genes, the chemotaxis of other smell would not be affected.3. Localization of GPCRs STR-193and STR-7in sensory neurons.It has been shown there existed1000GPCRs in C. elegans, most of which are believed to function as chemoreceptors. Here, we construct the expressional plasmids of STR-193::GFP and STR-7::GFP to detect the their localization in the neurons. Our results showed that STR-193was localized in the AWC neurons.4. Confirming the other components in olfactory signal pathways for sensing indole and2-ethy1hexanol.After testing the changes of chemotaxis to indole or2-ethyl hexanol via RNAi or function-lost mutants, a series of the candidate genes involved in the olfactory signaling pathway were proposed, including Ga (odr-3and gsa-1), guanylate cyclase (odr-land daf-11), cyclic nucleotide gating of ion channel subunits (tax-2and tax-4) and other elements. Meanwhile, the genes that were required to sense2-ethyl included hexanol Gα(odr-3and gpa-6),transient receptor vanilloid potential (ocr-2and osm-9). phospholipase C (plc-1and egl-8) and other elements. In conclusion, cGMP pathway should be the main olfactory pathway for the chemotaxis of indole. However,PLC and TRPV pathway would affect the olfactory sense of2-ethyl hexanol.Innovation of the paper are as follows:1.STR-193in AWC neurons is the GPCR to sense indole attraction, and STR-7in AWA neurons is the GPCR to sense2-ethyl hexanol attraction.2.Identification of the other components in olfactory signal pathways for sensing indole and2-ethyl hexanol.