Expression Profiles and Response to Exogenous Hormones of β-Fructofuranosidase Gene BmSuc1 in Silkworms(Bombyx mori)

[Objectives]In order to clarify the regulatory effects of insect hormones on the expression of BmSuc1 and provide a reference for further analysis of the function and expression regulation mechanism of BmSuc1,this study explored the expression profiles of BmSuc1 in different tissues and periods of silkworm larvae and the expression changes of BmSuc1 after treatment with exogenous hormones.[Methods]By using the real-time fluorescence quantitative PCR technique,the expression characteristics of BmSuc1 were detected in different periods,different tissues and after treatment with exogenous hormones during the development of silkworm larvae.The expression of BmSuc1 and 20E receptor gene USP was detected after RNA interference with double-stranded RNA(dsRNA)of USP.[Results]The relative expression of BmSuc1 gene in the midgut was the highest,followed by the silk glands,epidermis and hemolymph.However,there was much lower or almost no expression in other tissues.In addition,the BmSuc1 expression profile exhibited a pulse-like pattern in silkworm larvae.The expression level of BmSuc1 was higher at each instar stage before molting,late fifth instar before cocooning and prepupal stage.Silkworm larvae at day 2 of the fifth instar were treated with 20-hydroxyecdysone(20E)and juvenile hormone(JH).It was found that the expression of BmSuc1 was extremely significantly higher at 12 and 18 h after 20E treatment than the control group injected with 0.1%dimethyl sulfoxide(DMSO)(P<0.01,the same below).But there were no significant difference in BmSuc1 expression between the JH treatment and the control group during the measurement time range(P>0.05).The dsRNA of USP was synthesized in vitro and injected into silkworm larvae at day 3 of the fifth instar.It was showed that the USP relative expression was extremely significantly down-regulated at 24 and 36 h after injection,which indicated that dsRNA interference was successful.RNAi of USP would block 20E signal transduction,and the expression of BmSuc1 was inhibited and significantly down-regulated at 24 and 36 h after injection of dsRNA of USP(P<0.05).[Conclusions]The BmSuc1 expression peaks appeared in the molting of silkworm larvae and the metamorphosis of larvae to pupae,which suggests that BmSuc1 may be involved in the metamorphic development process of silkworms.Treatment with exogenous ecdysone 20E can activate the expression of BmSuc1,but blocking the 20E signal transduction pathway may suppress expression of BmSuc1.It indicates that BmSuc1 as a downstream target gene in the 20E signal transduction pathway is directly or indirectly regulated by 20E signals.