DDX6 Is Essential for Oocyte Development and Maturation in Locusta migratoria

SIMPLE SUMMARY: Insect reproduction is an important and complicated process required for producing healthy individuals and maintaining their population abundance. Thus, it could become a valuable target for insect biological control. To date, many factors and pathways have been revealed to be involved in this reproductive process, but it is still far from a full understanding of the molecular network underlying this process. We herein investigated a RNA helicase, DEAD-box protein 6 (DDX6) in Locusta migratoria, a global, destructive pest, and found that knockdown LmDDX6 downregulated expression levels of juvenile hormone receptor gene methoprene-tolerant and its target genes 78-kDa glucose-regulated proteins, thus reducing vitellogenin expression and ultimately impairing the ovary development and oocyte maturation. These results demonstrate that LmDDX6 is a key player in female locust reproduction, providing, thus, a novel target for locust biological control. ABSTRACT: DEAD-box protein 6 (DDX6) is a member of the DDX RNA helicase family that exists in all eukaryotes. It has been extensively studied in yeast and mammals and has been shown to be involved in messenger ribonucleoprotein assembly, mRNA storage, and decay, as well as in miRNA-mediated gene silencing. DDX6 participates in many developmental processes but the biological function of DDX6 in insects has not yet been adequately addressed. Herein, we characterized the LmDDX6 gene that encodes the LmDDX6 protein in Locusta migratoria, a global, destructive pest. LmDDX6 possesses five motifs unique to the DDX6 subfamily. In the phylogenetic tree, LmDDX6 was closely related to its orthologs in Apis dorsata and Zootermopsis nevadensis. RT-qPCR data revealed high expression of LmDDX6 in the ovary, muscle, and fat body, with a declining trend in the ovary after adult ecdysis. LmDDX6 knockdown downregulated the expression levels of the juvenile hormone receptor Met, and genes encoding Met downstream targeted Grp78-1 and Grp78-2, reduced LmVg expression, and impaired ovary development and oocyte maturation. These results demonstrate that LmDDX6 plays an essential role in locust female reproduction and, thus, could be a novel target for locust biological control.