| Nematodes are parasitic in the root of plant,and have effect on the growth of crops,fruit yield and quality,and crop yield,this make great loss in agriculture and forestry industry.There are also a variety of bacteria in the soil,some of which have insecticidal effects on nematodes.Nematodes can distinguish between edible bacteria and pathogenic bacteria by sensing water-soluble substances,volatile substances,temperature,pH or permeability to feel the changes of environment,and then worms produce chemotaxis or avoiding behavior.The series of behaviors mainly relies on the olfactory nerves of nematodes,this not only because of the rapid detection of the olfactory nerve,but also because it can respond quickly to signals.The early stage of the experiment found Bacillus mycoides with biological activity against nematodes.By separating and purifying techniques,it was found that the chemical compound which has anti-nematode activity was styrene,and found that styrene also has avoiding effect to the nematodes.This study focused on the complete signaling pathway of the sensor-repellent signal molecule styrene.So we were able to clarify the interaction between the pathogens and their hosts as well as underlying the molecular mechanism.These results laid to a theoretical foundation for the use of pheromones in nematode biological control.The results of the experiment are as follows: 1.To determine the neurons that mediate nematode to sense the repellent styreneThe results showed that AWB was the neuron that was used to detect styrene in the C.elegans.2.To determine the GPCRs that mediate nematode to sense the repellent styreneIn screening of GPCRs,mutants che-3,dop-3 and str-2 were found that the ability of avoiding styrene are reduced,and the activity of mutant strains is normal,so can confirm CHE-3,DOP-3 and STR-2 are the GPCRs which mediated nematodes avoid styrene.3.To determine the G protein that mediate nematode to sense the repellent styreneThere are 21 G proteins in the nematodes olfactory pathway.The gpa-3 and gpa-7 mutants were found that the ability of avoiding styrene are reduced,while other mutants can detect styrene as well as the wild type.Therefore,it is essential to determine that GPA-3 and GPA-7 are the G proteins which mediated nematodes sense styrene.4.To determine the intracellular ion channels that mediate nematode to sense the repellent styreneThe results show that the avoiding index of mutants daf-11,odr-1,tax-4,tax-2,egl-8,plc-1,ocr-2 and osm-9,were significantly reduced compared with wild type.So all of these mutants: daf-11,odr-1,tax-4,tax-2,egl-8,plc-1,ocr-2 and osm-9 are related with the intracellular ion channels which mediate sense styrene.These mutants are: receptor nucleotide cyclase(daf-11 and odr-1)and cyclic nucleotide-gated ion channel(tax-2 and tax-4),phospholipase C(egl-8 and plc-1)and transient receptor potential vanilloid channel(osm-9 and ocr-2).In summary there were two ion channels to sensing and detecting styrene in worms.One of the signal pathways was cGMP signal and CNG channel,the other signal pathways are the PLC and the TRPV channels.In addition the calcium channel CMK-1 and IP3 receptors on the downstream of the ion channel are also involved in regulating the perception of styrene.Another olfactory pathway could also sense styrene that was mediated by BAG neuron and toll-like receptors.In this study,we found that tol-1,trf-1,mom-4,ikb-1,and pmk-3 mutants were defective for styrene-avoidance behavior and found some of these mutants exhibited severe behavioral defects.The related genes for insect resistance in R2 were screened by constructing cosmid gnomic library. |
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