An SMC-domain protein regulates eupyrene spermiogenesis and sperm migration in a cosmopolitan insect, Plutella xylostella.

Reproductive capacity is a key determinant of the global success of agricultural insect pests and depends fundamentally on efficient spermatogenesis. In Lepidoptera, however, the molecular mechanisms regulating sperm development and migration remain largely unknown. Here, we functionally characterized an SMC-domain-containing gene, PxSMC, in the diamondback moth, Plutella xylostella. PxSMC exhibited strong testis-specific expression, suggesting a role in male reproductive development. CRISPR/Cas9-mediated disruption of PxSMC caused complete male sterility without affecting female fertility. Mutant males displayed prolonged mating duration, delayed oviposition, and produced predominantly unfertilized eggs. Cytological and post-mating analyses revealed reduced spermatophore size and abnormal retention of sperm within female reproductive organs, indicating impaired sperm transfer and migration. Further examination showed that loss of PxSMC disrupted nuclear organization within eupyrene sperm bundles, leading to defective spermiogenesis. Collectively, these results demonstrate that PxSMC is essential for eupyrene sperm development and successful sperm migration in P. xylostella. Our findings identify a previously uncharacterized SMC-domain regulator of insect spermatogenesis and provide molecular insights into reproductive biology that may inform genetic strategies for sustainable pest management.