SPSL1 is essential for spermatophore formation and sperm activation in Spodoptera frugiperda.

The reproductive process in various species has undergone evolutionary adaptations at both the physiological and molecular levels, playing a significant role in maintaining their populations. In lepidopteran insects, the spermatophore is a unique structure formed in the female reproductive system, in which sperm storage and activation take place. It is known that the formation of the spermatophore is regulated by seminal fluid proteins derived from males. However, studies investigating the genetic mechanisms behind spermatophore formation in lepidopterans have been limited. In this study, our focus was on SPSL1, a gene that encodes a trypsin-type seminal fluid protein in Spodoptera frugiperda, a pest species with global invasive tendencies. Our findings revealed that SPSL1 expression was predominantly observed in the male reproductive tracts, and the disruption of this gene resulted in male sterility. Surprisingly, fluorescence analysis indicated that the absence of SPSL1 did not affect spermatogenesis or sperm migration within the male reproductive system. However, when females mated with SPSL1-mutant males, several defects were observed. These included disruptions in spermatophore formation, sperm activation in the copulatory bursae, and sperm migration into the spermathecae. Additionally, mass spectrometry analysis highlighted reduced levels of energy-related metabolites, suggesting that SPSL1 plays an essential role in promoting hydrolysis reactions during copulation. Consequently, our study demonstrates that SPSL1 is crucial for male fertility due to its functions in spermatophore formation and sperm activation. This research provides valuable insights into the genetic factors underlying reproductive processes in lepidopteran insects and sheds light on potential strategies for controlling invasive pest populations. Author summary: In lepidopteran insects, males produce a spermatophore to deliver the sperm during copulation and promote reproductive success. Seminal fluid plays a crucial role in the formation of spermatophore and the regulation of sperm activation. However, little is known about the semen protein molecules involved in these processes. In this work, we used Spodoptera frugiperda as a model to study the function of the seminal fluid protein SPSL1, a trypsin-type serine protease, in the reproductive process. By analyses of insects with a loss-of-function mutation in SPSL1, we found that SPSL1 affects the structure of the spermatophore, sperm activation, sperm distribution, and sperm migration in the female reproductive tract. Our research deepens our understanding of the reproductive process of lepidopterans and demonstrates that SPSL1 is a potential target for novel pest control methods such as sterile insect technology. [ABSTRACT FROM AUTHOR]