Bacterial infection induceس RNA interference (RNAi) pathway in the cotton bollworm, Helicoverpa armigera
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
RNA interference (RNAi) is an extremely conserved regulation and defense mechanism which suppresses gene expression via reducing targeted RNA. RNAi directed by either exogenous small interfering RNAs (siRNAs) or endogenous microRNAs (miRNAs); siRNA include naturally occurring dsRNA, such as that originating from virus infections, and dsRNAs experimentally produced and introduced. MiRNAs include short hairpin RNAs produced by the genome, aberrantly expressed transgenes, and transposons that have appeared as important regulators of various biological processes including development, cancer, immunity, and host–microorganism interactions. The RNAi responses have been suggested as an ancient antiviral immunity in metazoans including insects. In this study we questioned whether RNAi induced by bacterial infection. To do this, we focused on Dicer1and Dicer2 genes (encoding ribonuclease III enzymes) that are important factors in miRNA and siRNA pathway, respectively. To identify these genes in H. armigera, we considered mRNAs from whole transcriptome sequences and ESTs extracted from NCBI as well. By Blast search we found Dicer1 and Dicer2 in the transcriptome dataset of H. armigera which showed high similarity to the homologous sequences in Spodoptera exigua. To investigate induction of RNAi response, we injected either Bacillus thuringiensis or Serratia marcescens into hemolymph of fifth-instar larvae of cotton bollworm while ds water was injected into the control insects. Total RNA samples were extracted from whole body of the bacterial-injected larvae and the controls at different times post injections (i.e. 6, 12, 24, 48 and 72 hpi) and cDNA libraries were synthesized by using RT-PCR and oligodT primer. Expression levels of the target genes were analyzed by RT-qPCR utilizing RPL27 as the reference to normalize gene expressions. Our results showed that expression levels of Dicer1 and Dicer2 were increased respectively at 12 and 48 hours post injection in the infected larvae while there was no change in expression levels of these genes in the control larvae. Silencing of Dicer1 and Dicer2 by using specific dsRNA modulated bacterial replication that showed their roles in bacterial infection of H. armigera. In conclusion, it seems that RNAi immunity is important not only in viral infection of insects but also in bacterial infections.
کلیدواژه ها