The assembly of Y chromosome reveals amplification of genes regulating male fertility in Bactrocera dorsalis

BACKGROUND: The oriental fruit fly Bactrocera dorsalis is an invasive pest causing considerable ecological and economic damage worldwide. The Y chromosome is an important target for the sterile insect technique (SIT) but its sequence and structure has been poorly explored. RESULTS: We assembled the genome of B. dorsalis at the chromosome level with a total size of 562.6 Mb. The assembly includes a ~7.6 Mb Y chromosome sequence, being the first reported Y chromosome in Tephritidae. The assembled Y chromosome is highly repetitive, and contains 61 genes, including 9 multi-copy genes. We surprisingly found that the M factor (MoY) in Tephritidae has multiple copies, verified by our droplet digital PCR (ddPCR) analysis. Besides, we identified 32 copies of gyf-like on the Y chromosome (gyfY) that were highly expressed in testis. RNAi targeting the gyfY resulted in depletion of live sperms, suggesting that the amplification of gyfY is essential for male fertility, which facilitated the understanding of high fecundity of this invasive insect. CONCLUSION: We reported firstly the Y chromosome of Bactrocera dorsalis. Our results will also provide target genes for CRISPR/Cas9 based SIT, leading to the development of novel control strategies against tephritid flies.