Molecular cloning, expression profiling and RNA interference of a vitellogenin gene from Harmonia axyridis (Coleoptera: Coccinellidae)

In this study, the Harmonia axyridis vitellogenin gene 2 (HmVg2) sequence was identified from transcriptomic databases of female adult H. axyridis and cloned into pMD18-T vector. The HmVg2 gene was 5460 bp in length, and formed with an open reading frame (ORF) of 5 361 nucleotides (GenBank accession no. KY794939). The putative molecular weight of the primary HmVg2 protein was 203.459 kDa and the predicted isoelectric point (pI) was 8.59. HmVg2 contained a signal peptide, vitellogenin N-terminal (vitellogenin-N) domain, domain of unknown function 1943 (DUF1934) domain and von Willebrand factor type D (VWD) domain. The developmental expression profiling showed that HmVg2 was extremely highly expressed in female insects, but was expressed at lower levels in male insects. In female insects, HmVg2 was mainly expressed in the wing and fat body. The double-stranded RNA-HmVg2.-GFP was injected into H. axyridis, and qRT-PCR results showed that the HmVg2 gene was specifically silenced. The eggs laid during the first five days and the hatching rate of eggs was lower than controls after dsHmVg2 injection. This investigation demonstrated that the HmVg2 gene plays an important role in H. axyridis reproduction and enriches the function of the insect vitellogenin gene.