| The symbiosis of insects and microbes,especially fungi,is one of the main driving forces for insects to develop from a collective life to a completely social life.The use of fungi by termites is an important symbol of their social evolution.Previous studies in our lab showed that worker of Reticulmes labralis collect Fibulorhizoctonia sp.from outside and then put them in their nest.The compound eyes of worker have been degenerated,and the recognition of external signals mainly relies on the olfactory sensors on the antennae.In order to explore the effect of the R.labralis on the fungus Fibulorhizoctonia sp.,we observed the antennal sensilla types of R.labralis that moves the sclerotium and R.aculabialis that does not move the sclerotium by scanning electron microscopy;The olfactory related genes were screened out from the transcriptome databases of the two species,and the differences of olfactory related genes expression levels were compared between the two species with and without sclerotaria in the nests;GC-MS was used to analyze the volatile substances produced by the fungus Fibulorhizoctonia sp.that may be attractive to worker.It provides a basis for revealing the molecular mechanism of the recognition of the fungus Fibulorhizoctonia sp..The main findings and conclusions of this study include:1.Comparison of the microstructures of the workers’ antennae of the R.labralis and R.aculabialis.The antennae of the female and male worker of the two species of termites are typical rosary-like structures,which are composed of three parts: Scape、Pedicel、Flagellum,but the number of antennae may be different between different individuals.The antennae of female worker of R.labralis have 14-16 segments,male worker have 15-17segments;the antennae of female worker of R.aculabialis have 11-16 segments,male worker have 12-16 segments.The antennae length of the female worker of R.labralis is 1360.5±120.1 μm(n=10),male worker of R.labralis is 1319.2±66.1 μm(n=10);the antennae length of the female worker of R.aculabialis is 1374.5±71.5 μm(n=10),male worker of R.aculabialis is1289.0±70.9 μm(n=10)There is no significant difference in the basic structure of the antennae between R.labralis and R.aculabialis.2.Using Scanning Electron Microscope to determine the antennae types of R.labralis and R.aculabialis worker.In this study,we observed 10 antennae sensillas of six categories in the antennae of these two kinds of worker termites.They are B(?)hm bristle(BB),Sensilla trichodea 1(ST1),Sensilla trichodea 2(ST2),Sensilla chaetica 1(SC1),Sensilla chaetica 2(SC2),Furcella shape sensilla campaniformia(X),Sensilla campaniformia(SCA),the intermedius type sensilla campaniformia(similar to the sensilla campaniformia and the furcella-shape sensilla,X/SCA),hemisphere Sensilla(SH)and a surface hole structure(Aperture).The hemispherical sensilla(SH)was only observed in female and male worker of R.labralis,and the Aperture structure was only observed in female worker of R.labralis.However,neither structure was found in the antennae of the worker termite.The results of this study indicate that the types of antennae sensillas of the R.labralis and R.aculabialis are different,which may be related to the differences in environmental adaptation and behavioral functions of the two types of workers.3.qRT-PCR was used to analyze the different expression of olfactory related genes in workers with and without sclerotia in the nest.22 olfactory related genes were annotated in our transcriptome data of the R.labralisworker,including 17 odorant binding protein(OBPS)genes,1 chemosensory protein(CSPS)gene and 4 odorant receptor(ORS)genes;33 olfactory related genes were annotated in our transcriptome data of the R.aculabialis worker,including13 odorant binding protein(OBPS)genes,18 chemosensory protein(CSPS)gene and 2odorant receptor(ORS)genes.After primer specific screening,13 olfactory related genes were screened in R.labralisworker.It was found that the expression levels of 10 olfactory protein-related genes were significantly higher in the presence of sclerotinia than in the absence of sclerotinia(P < 0.05),the other 3 olfactory protein-related genes(GOBP 56d、OBP3、GOBP 19a)were not significantly different in the presence of sclerotinia and the absence of sclerotinia.15 olfactory-related genes were screened out from the R.aculabialis worker.It was found that the expression levels of only 4 olfactory protein-related genes(GOBP 19a、OBP 2、CSP、CSP)in the worker ants were significantly higher than those of the worker ants without sclerotium in the nest(p<0.05),the expression levels of the remaining 11 olfactory protein-related genes were not significantly different in worker ants with and without sclerotium in the nest.Therefore,it can be inferred that Fibulorhizoctonia sp.can stimulate the CSPs,CSPs and ORs on the olfactory receptors of the R.labralis worker to recognize them.4.Analyze the volatile substances produced by the fungus Fibulorhizoctonia sp.during the germination process by GC-MS.By comparing with the chemical spectrum library,12 kinds of volatile component were analyzed,which are hexanol,octanol,linalool,E-orange tertiary alcohol,pinealester,ketone,tertiary alcohol,ethyl tetradecate,pentadecane,palmitol,lauryl alcohol,eicosane and 2,4-ditert-butylphenol.The most volatile components are hexanol and octanol.Most of these volatile compounds are mainly alcohols with woody fragrance,which may have a strong attractive effect on worker,the R.labralis worker may recognize Fibulorhizoctonia sp.through these(or a certain)volatiles and then carry them into the nest.In summary,the recognition effect of termites on the fungus Fibulorhizoctonia sp.is the result of the interaction between olfactory organs and external odor molecules.Worker recognize and receive external odor molecules through various olfactory sensors on their antennae,while the fungus Fibulorhizoctonia sp.produces volatile compounds that may be attractive to worker,which in turn leads to their handling behavior.This article first discovered that the fungus Fibulorhizoctonia sp.has a significant olfactory stimulus to the R.labralis worker,and analyzed the volatile substances of Fibulorhizoctonia sp.,these studies not only shed light on termites and Fibulorhizoctonia sp.,it can also provide a new idea for the control of Reticulitermes. |
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