Silencing LdBr-C Impairs Larval Development And Chitin Synthesis In Lymantria Dispar Larvae

In insects,the 20-hydroxyecdysone(20E)mediates developmental transitions and regulates the molting processes through activation of a series of transcription factors.Previous reports had confirmed that Chitin synthesis could can be promoted by 20E during insect molting,but which the responsive gene triggers chitin biosynthesis stillgene(s)responsible remains largely unclear.Broad-Complex(Br-C),as a vital gene in the 20E signaling pathway,plays crucial roles during insect growth processes.However,whether Br-C affects the chitin synthesis of chitin in insects and how does this transcription factor regulate chitin biosynthesis remains unclear,and the transcription factors regulating chitin biosynthesis are unknown.In the present study,the Br-C gene from Lymantria dispar,a notorious defoliator of forestry,was firstly identified based on the transcriptome data,and subjected to its bioinformatics analysis was investigated.Furthermore,the regulatory functions of LdBr-C in regulating chitin synthesis and metabolism of chitin in L.dispar larvae was were analyzed by RNA interference(RNAi).The full-length LdBr-C gene(1431 bp)encodes a 477 amino acid(aa)polypeptide containing a common BRcore region(391 aa)at the N-terminus and a C-terminal Zinc finger domain(56 aa)harboring two characteristic C2H2 motifs(CXXC and HXXXXH).Phylogenetic analyses showed that LdBr-C has the shares highest homology and identity with the Br-C isoform 7(83.12%)of Helicoverpa armigera.Expression profiles indicated that LdBr-C was expressed throughout larval and pupal stages,but and highly expressed in the prepupal and pupal stages.Furthermore,LdBr-C expression was strongly induced significantly by the exogenous 20E,and suppressed dramatically after application of dsLdBr-C.Bioassay results showed that knockdown of LdBr-C caused larval developmental deformity,a significant weight loss,and a mortality rate of 67.18%.The qRT-PCR results revealed that knockdown of LdBr-C significantly down-regulated transcription levels of eight critical genes(LdTrel,LdTre2,LdG6PI,LdUAP,LdCHS1,LdCHS2,LdTPS,and LdCHT)related to chitin synthesis and metabolism,caused a significant decrease ofthereby lowering the chitin content in the midgut and epidermis.Our findings demonstrate that Br-C knockdown impairs larval development and chitin synthesis in L.dispar.