Preliminary Study On Differential Expression Of Glucose Oxidase In Labial Gland Between Helicoverpa Armigera And H. Assulta

The noctuid Helicoverpa armigera and H.assulta are sibling species,but have vastly different host breadth.H.armigera is a generalist feeding more than200 plants from 30 families,while H.assulta is a specialist feeding only on plants in the genus Solanum.Due to the potentially broad importance of the salivary enzyme glucose oxidase(GOX)to caterpillar fitness,such as host plant utilizing,and major role in interactions between host plant and caterpillar feeding.We conducted this study to evaluate whether and how generalist and specialist feeding habits are reflected in differences in their GOX gene transcription level and GOX activities.1.The comparison of labial gland transcriptome data between H.armigera and H.assultaRNA-seq provides a great opportunity to explore genome-scale transcriptional patterns with tremendous depth.The difference in transcriptome data of labial gland between polyphagous H.armigera and the oligophagous H.assulta was compared.In the end,we focus on the target gene GOX from the background of the two sibling species labial gland transcriptome data.The RPKM of GOX gene in H.armigera and H.assulta was 5020.8 and 4503.5,respectively.2.The dynamic changes of GOX activity in H.armigera and H.assultaThe labial gland is composed of four parts,belongs to N type.The activity of GOX was different in the different larval instars and even in different stages of the same instar.In order to make clear the dynamic changes of GOX activity in these two sibling species,GOX activity and relative growth rate were investigated after molting into last instar,every 12 h until 72 h.The results showed that the two sibling species had the hightest GOX activity at 12 h after head capsual slippage to last instar.The highest activity of H.armigera was 7.3 times compared with that of H.assulta.The difference is that the GOX activity of H.armigera reduced after 48 h,but H.assulta did after 60 h.They both had low GOX activity at the beginning of the last instar and before prepupal stage.Corresponding to high GOX activity,the relative growth rate of two species larvae reached highly during the active feeding period.This suggested that the activity of GOX is closely related to the feeding of caterpillar.3.The regulation of dietary factors on libial gland GOX gene transcriptional level of the two sibling speciesThere is great difference of GOX activity among different insects.According to the close relationship between GOX of caterpillars and their diets,we made the two sibling species feed different diets to explore the main dietary factors which cause the change of GOX gene,then analysis GOX acitivity in next,to make clear whether the change is regulated at transcriptional level,or translation and/or post-translation level.The results showed that the level of GOX gene in polyphagous H.armigera could be induced by the comparatively poor host plant pepper,its level was significantly higher than that of the control.As for oligophagous H.assulta,all three host plants can induce significantly higher expression of GOX gene compared with the control.The transcriptional level of GOX gene of H armigera was not significantly affected by the ratio of dietary proteins and digestible carbohydrates(P: C),except for 50 p: 50 C.However,the level of GOX gene of H.assulta increased with the increase of carbohydrate concentration.No significant changes of GOX gene in H.armigera larvae when feeding on diets treated with different plant toxin.However,the expression of GOX gene in H.assulta could be significantly induced by flavone,2-tridecanone,xanthotoxin and coumarin,respectively.These suggested that GOX gene ofoligophagous H.assultawas more sensitive to dietary factors than that of polyphagous insect H.armigera.4.The effects of dietary factors on libial gland GOX activity of the two sibling speciesComparative studies of the change of the GOX activity in labial salivary glands of the last instar larvae fed with artificial diet,three host plants,and the major dietary factors responsible for such variations were investigated in these two sibling species.The results showed that three host plants exerted different effect on the GOX of two species,but they both had the highest amount of GOX activitywhen feeding on the comparatively poor host.Until now,the nutritional or phytochemical factors that may contribute to GOX differences observed in larvae feeding on various host plants are not clearly known.Although the ratio of dietary proteins and digestible carbohydrates(P: C)did not significantly affect GOX activities of two species,the GOX activity increased with the increase of the dietary glucose in H.armigera.Furthermore,the labial salivary GOX activity was determined after caterpillars were fed with artificial diets containing 12 plant toxins,respectively.The results showed that the GOX activity of two sibling species expressed different patterns,H.assulta is more sensitive to flavore,coumarin,and xanthotoxin than H.armigera,and tolerant to capsaicin and nicotine,which are the main allelochemicals in its lovely feeding host plant.Almost in all experiments,polyphagous H.armigera possess remarkably higher levels of GOX compared to oligophagous H.assulta.This suggests that generalist H.armigera possibly use GOX as a constitutive adaption to allelochemicals,whereas oligophagous H.assulta use induced adaptation,the mechanisms of which remain to be investigated.