Expression and Role of Vitellogenin Genes in Ovarian Development of Zeugodacus cucurbitae

SIMPLE SUMMARY: Vitellogenin (Vg) is the precursor of the yolk protein gene, which is crucial for insect reproduction. In this study, we identified four Vg genes in Zeugodacus cucurbitae (Coquillett). Their molecular characteristics and expression patterns were analyzed. The four genes are mainly expressed in the fat body tissue of adult female melon flies, and their expression is regulated by the juvenile hormone and ecdysone. Nutritional stress significantly down-regulated their expression, indicating that nutrition-dependent vitellogenic development occurs during ovarian development. RNAi-mediated inhibition of the expression of the four genes resulted in significantly delayed ovarian development in Z. cucurbitae. The results indicate that the four genes play an important role in the development of ovaries in Z. cucurbitae. ABSTRACT: Vitellogenin (Vg) genes encode the major egg yolk protein precursor in arthropods. In this study, four Vgs were identified in Zeugodacus cucurbitae (Coquillett). Sequence analysis showed that four ZcVgs had the conserved Vg domain. Phylogenetic analysis indicated that four ZcVgs were homologous to the Vgs of Tephritidae insects. The temporal and spatial expression patterns of ZcVgs were analyzed by quantitative real-time polymerase chain reaction (RT-qPCR), and the four ZcVgs showed high expression levels in female adults, especially in the fat body. The expression of ZcVg1 and ZcVg3 was down-regulated by a low dosage (0.5 μg) of 20-hydroxyecdysone (20E), and ZcVg2, ZcVg3, and ZcVg4 were up-regulated by a high dosage (1.0 and 2.0 μg) of 20E. The expression of ZcVg1 and ZcVg2 was up-regulated by 5 μg of juvenile hormone (JH), while all of the ZcVgs were down-regulated by a low and high dosage of JH. Expression of ZcVgs was down-regulated after 24 h of starvation and recovered to normal after nutritional supplementation. After micro-injection of the gene-specific double-stranded RNA, the ZcVgs’ expression was significantly suppressed, and ovarian development was delayed in Z. cucurbitae females. The results indicate that RNA interference of reproduction-related genes is a potential pest control method that works by manipulating female fertility.