Structure And Gustatory Function Of Proboscis Of Plutella Xylostella.L

Diamondback moth Plutella xylostella L.is one of the major pests of cruciferous plants.After emergence,the moth sucks honeydew with siphoning mouthpart to maintain the life activities during mating,host selection and oviposition.However,there has been no report on the structure and function of the proboscis.This feeding preferences of P.xylostella moth for different types of sugar and the effect of bitter substances was investigated.Scanning electron microscopy(SEM)was used to observe the structure and sensilla type in the moth.Through the preliminary transcriptome assay,three taste receptor genes were screened and the expression of these three genes in some tissues was detected by fluorescent quantitative PCR.The preliminary mechanism of the taste perception of P.xylostella was illustrated.The specific findings are as follows:1.The fine structure of proboscis of P.xylostella moth.The mouthparts of the diamondback moth are composed of labial palpi and proboscia located in the middle,proboscis formed by two extended galea chain locks.The proboscia dorsal linkage method is mainly through the overlapping of the lance-shaped plates on the upper and lower sides,and the upper lance-shaped plates overlap only near the top of the fistula.The ventral linkage is interlocked by galeae interlocking hooks.Each toothed hook consists of similarly shaped upper and lower toothed hooks.From the base of the proboscis to the top,the toothed hooks gradually increase in length,but the upper toothed hooks are longer than the lower toothed hook,there is a gap between the two toothed hooks for the insertion of the opposite toothed hooks.2.Sensitivities of the diamondback moth to the sweet and the bitter stimuli.When 100 mM sucrose,fructose,maltose,and trehalose were used to stimulate the antennae of male and female of P.xylostella,they all caused proboscis extension reflex.Among them,the response to sucrose was the most significant,response rate over 60%,and the response to fructose was the least obvious,the rate was 20%.For different types of sweet substances,the variation in males' responses was insignificant,and so only females were subsequently tested.However with the increase of the concentration of sugar solution,the elongating response of the female proboscis was not significantly enhanced.The females were sensitive to the three bitter substances:quinine,benzodiazepine,and berberine.At lower concentrations,the repellent behavior of P.xylostella d the repellent response rate was over 90%.3.The classification and function of the sensilla on proboscis of P.xylostella moth.Sensilla on P.xylostella moth proboscis are classified sensilla chaetica,sensilla basiconica and sensilla styloconica.Among them,sensilla basiconica is divided into two subtypes of external sensilla basiconica(ESB)and internal sensilla basiconica(ISB)depending on the distribution position.With the nerve backfilling of P.xylostella proboscis,it was found that the sensilla on the proboscis projected into suboesophageal ganglion,and it revealed that the sensilla function are gustatory.4.Cloning and tissue expression analysis of three kinds of taste receptor genes in the diamondback moth.From three taste receptor gene found on the proboscis in the moth,three full-length sequences of taste receptor genes were cloned and named as PxyGr1,PxyGr2 and PxyGr3.The open reading frame of PxyGrl is 1443bp in length and encodes 481 amino acids.The open reading frame of PxyGr2 is 1020bp in length and encodes 340 amino acids.The open reading frame of PxyGr3 is 1401 bp in length and encodes 467 amino acids.By establishing an evolutionary tree and sequence alignment,it is suggested that PxyGrl,PxyGr3 may be C02 receptor,and PxyGr2 may be a sugar receptor.qPCR results showed that PxyGrl was only expressed in the antenna and proboscis of the moth,and PxyGr2 and PxyGr3 were expressed in the antenna,the leg,the labial palpi and the proboscis,but PxyGr2 was extremely low in the labial palpi,and PxyGr3 was in the labial palpi.The highest level of expression,in other organizations,the expression is extremely low.