Role Of Genes Involved In Juvenile Hormone Degradation During Diapause Preparation Of Colaphellus Bowringi

Insect juvenile hormone(JH)plays a key role in regulating adult's reproduction and diapause.The lack of JH may lead the adults into reproductive diapause.JH titer in insects is regulated by both biosynthesis and degradation.Previous studies in insects have demonstrated the suppression of JH biosynthesis is an important reason for JH absence in adults which induces reproductive diapause.However,it is not clear that whether JH absence in adults caused by the JH degradation increase may also contribute to reproductive diapause.JH degradation mainly relies on there enzymes: juvenile hormone esterase(JHE),juvenile hormone epoxide hydrolase(JHEH)and juvenile hormone diol kinase(JHDK).Krüppel homolog 1(Kr-h1),an indicator gene which responds to JH signaling,was consistently lowly expressed during the period of diapause-preparation in Colaphellus bowringi,suggesting that the JH signaling is lack in the diapause-destined adults.In this study,the role of genes involved in JH degradation was studied during diapause preparation in C.bowringi,which would provide a reference for revealing the molecular mechanism of reproductive diapause incidence in insects.The main results are as follows:1.Cloning and sequence analysis of JH degrading enzyme geneThe c DNA sequences of 3 JHEs(JHE1,JHE2,JHE3),1 JHEH and 1 JHDK were cloned from C.bowringi.Sequence alignment and phylogenetic tree results showed that JHEs,JHEH and JHDK of C.bowringi all contained the corresponding JH degrading enzyme conserved and active motifs which are responsible to JH degradation,suggesting that these enzymes may participate in JH degradation in C.bowringi.2.The expression of JH degrading enzyme genes are regulated by JH SignalingExpression patterns of JH degrading enzyme genes indicated that JHEs were lower expressed in non-diapause-destined adults,while JHEH and JHDK were more highly expressed in diapause-destined adults.Therefore,in diapause-destined adults which lack JH signal,it could be speculated that JHEH and JHDK but not JHEs were involved in JH degradation.The knockdown of JH receptor Methoprene-tolerant(Met)and exogenous application of JH analog indicated that JHE transcriptions were upregulated,while bothJHEH and JHDK transcriptions were downregulated by JH signal.These results suggested that there should be a feedback regulation between JH signal and transcription of JH degrading enzyme genes.Moreover,JH signal may regulate the differential expression of JHEs,JHEH and JHDK in non-diapause-destined and diapause-destined adults of C.bowringi.3.Role of JH degrading enzyme genes during diapause preparation of C.bowringiThe transcription of Kr-h1 was upregulated,lipid accumulation and stress resistance signal were downregulated when JHEH or JHDK was knocked down in diapause-destined adults by RNAi.Meanwhile,the transcription of Vg1 was upregulated when JHEH was knocked down.However,diapause phenotypes were not fully reversed in diapause-destined adults when JHEH or JHDK was knocked down.The study showed that,JHEH and JHDK in JH degrading pathway may facilitate diapause preparation.But it could not be a decisive factor for reproductive diapause incidence in C.bowringi.These results would shed light on the molecular mechanism of reproductive diapause incidence in insects.