Molecular Identification and Functional Characterization of Vitellogenin Receptor From Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Abstract Vitellogenin receptors (VgRs) have vital roles in reproduction by mediating endocytosis of the vitellogenin (Vg) in oviparous insects. Same as most insect species that possess only one VgR, in this study, a single VgR mRNA (HmVgR) was identified in an important natural enemy ladybeetle, Harmonia axyridis (Pallas). The open reading frame of HmVgR was 5,340 bases encoding a protein of 1,779 amino acids. Bioinformatic analyses showed that HmVgR had conserved domain motifs of low-density lipoprotein receptor family. Based on phylogenetic analysis, HmVgR had highly homologous within the Coleoptera. The transcriptional level of HmVgR was initially detected in the newly emerged female adults, gradually increased from day 3 to day 9, peaked on day 13, and then sharply decreased on day 15. Similar to most insects, HmVgR was expressed specifically in ovarian tissue. Moreover, RNA interference (RNAi) clearly decreased the transcription levels of HmVgR, which blocked the deposition of yolk protein in the ovaries, shortened the ovarian length, and led to negative impacts on reproductive-related parameters (i.e., prolonged preoviposition periods, reduced spawning and depressed hatchability). In sum, these results indicated that HmVgR may be critical for yolk protein deposition of oocytes and can play a key role in reproduction of female adults of H. axyridis. Our results provide conclusive proof for the important roles of HmVgR in fecundity, and establish a basis for further research on its interaction with vitellogenin.