Possible Regulation of Larval Juvenile Hormone Titers in Bombyx mori by BmFAMeT6

SIMPLE SUMMARY: Juvenile hormone (JH) is very important to the growth and development of insects, but the role of farnesoic acid O-methyltransferase (FAMeT) on JH titer has not been determined in insects. In this study, BmFAMeT6 overexpression and BmFAMeT6 knockout strains were established by using the Gal4/UAS binary hybrid system and CRISPR/CAS 9 system, respectively. The role of FAMeT in the regulation of insect JH titers and the relationship between farnesoic acid and the synthesis of JH (JH I and JH II) were, first, revealed directly in insects. This provides a new perspective for further understanding the synthesis and regulation of JH in silkworms and other insects. ABSTRACT: Juvenile hormone (JH) plays a vital role in the growth, development, and reproduction of insects and other arthropods. Previous experiments have suggested that BmFAMeT6 could affect the duration of the silk moth’s larval stage. In this study, we established the BmFAMeT6 overexpression strain and BmFAMeT6 knockout strain using the GAL4/UAS binary hybrid system and CRISPR/Cas 9 system, respectively, and found that the larval stage of the overexpression strain was shorter, while the knockout strain was longer. Our results exhibited that both the JH titers and BmKr-h1 levels in the larvae of the third instar were reduced significantly by BmFAMeT6 overexpression, but were increased obviously by BmFAMeT6 knockout. In addition, injection of farnesoic acid induced changes in the JH I and JH II levels in the hemolymphs of larvae. This study is the first to directly reveal the role of BmFAMeT6 in the regulation of insect JH titers and the relationship between farnesoic acid and JH (JH I and JH II). This provides a new perspective on regulating the growth and development of insects such as Bombyx mori.