The Key Genes Regulate Nematode Defenses Against Predation By The N-Ematode-Trapping Fungus Arthrobot-Rys Oligospora

Arthrobotrys oligospora is a representative of nematode-trapping fungi,which preys on nematodes by producing three-dimensional adhesive nets.A.oligospora has the potential to be used as biological control agent for parasitic nematodes of plants and animals and has a broad application prospect in biological control of pathogenic nematodes.However,little is known about the mechanism of interaction between A.oligospora and nematodes.In this paper,we investigated the mechanism by which nematodes resist predation by A.oligospora.Firstly,we found that the ability of A.oligospora to prey on nematodes starved for 24 hours was reduced.LC-MS analysis showed that the abundance of ascr #1,ascr#3,ascr #5,ascr #7 and ascr #9,which affected the trap-producing of A.oligospora,were decreased in C.elegans after 24 hours starvation.At the same time,m RNA expression levels of acyl-Co A oxidase genes（acox-1.2,-1.3 and-1.4）,which are important in ascarosides synthesis,were decreased in C.elegans after 24 hours starvation,and the fluorescence expression level of acox-1.2p::gfp was decreased after 24 hours starvation.These results suggested that starvation may lead to a low expression of acyl-Co A oxidase,which in turn leads to a decrease in ascarosides abundance,leading to a decrease in the predation of A.oligospora on nematodes.After silencing acox-1.2,acox-1.3 and acox-1.4 by RNAi in the nematodes,we observed the predation of the nematodes by A.oligospora.Our results showed that the percentage of acox-1.2,acox-1.3 and acox-1.4-silenced nematodes captured and the number of traps produced by A.oligospora were significantly reduced compared with empty vector.In addition,It has been shown that the expressions of a series of acyl-Co A oxidase family genes were significantly up-regulated in the glp-1（e2141ts）mutant.We found that the percentage of glp-1 mutant nematodes captrued and the number of traps produced by A.oligospora were also significantly increased compared with wild-type nematodes,indicating that the up-regulation of nematode acyl-Co A oxidase genes indeed promotes the predation of A.oligospora on nematodes.Further study showed that the fluorescence expression level of acox-1.2p::gfp was significantly decreased in worms after the nuclear receptor gene daf-12 was silenced by RNAi.The predation of A.oligospora on daf-12-silenced nematodes was significantly reduced compared with worms subjected to empty vector.These results suggested that the nuclear receptor DAF-12 positively regulates the expression of acyl-Co A oxidase,thereby regulating the synthesis of ascarosides,leading to increased the predation of A.oligospora on nematodes.We investigated the role of known nematode innate immune pathways in resistance to A.oligospora.These pathways include DAF-16 pathway,SKN-1/Nrf2 pathway,HLH-30 pathway,p38 MAPK pathway,ERK MAPK pathway,TGF-like DBL pathway,EGL-30 pathway,G-protein-coupled receptor FSHR-1 pathway,IRE-1/XBP-1 endoplasmal reticulum unfolded protein response and ATFS-1mitochondrial unfolded protein response.Our study showed that the survival rates of atfs-1 and fshr-1 mutants were significantly reduced compared with wild type under predation of A.oligospora.Furthermore,the expression level of mitochondrial companion HSP-60 was significantly increased under predation of A.oligospora.These results suggest that mitochondrial unfolded protein response is involved in resistance to predation by A.oligospora.p38 MAPK,as a classic immune-related genes,is involved in nematode resistance to the predation of A.oligospora.In contrast,the other pathways,such as DAF-16 pathway,HLH-30 signaling pathway,ERK MAPK pathway,were not involved in nematode resistance to the predation of A.oligospora.In conclusion,we studied the mechanism of nematode resistance to predation by A.oligospora,and identified a series of genes that are resistant and sensitive to predation by A.oligospora,providing new targets for nematode biocontrol.