LsFAMeT and LsJHAMT coordinate JH biosynthesis to regulate fecundity in Laodelphax striatellus

Farnesoic acid O-methyltransferase (FAMeT) and juvenile hormone acid O-methyltransferase (JHAMT) are key enzymes in the isoprene branch pathway, a specialized downstream biosynthetic pathway for juvenile hormone (JH). Both enzymes play crucial roles in insect egg production. While their mechanisms have been well characterized in model insects, this study aims to elucidate their specific functions in the reproductive process of the small brown planthopper (SBPH), Laodelphax striatellus. Here, we cloned the full-length cDNA encoding a putative FAMeT (LsFAMeT) from SBPH. The deduced protein sequence has a conserved Methyltransf_farnesoic acid domain and shares high identity with other insect FAMeTs. To gain further insight, we silenced LsFAMeT and LsJHAMT in SBPH and found that LsJHAMT expression increased when LsFAMeT was knocked down, and vice versa, suggesting a potential coordinated relationship between LsFAMeT and LsJHAMT in JH biosynthesis. In addition, RNAi-mediated silencing of LsFAMeT, LsJHAMT, or both genes significantly reduced female fecundity while simultaneously decreasing JH III titers. This was associated with reduced levels of total protein, cholesterol, triacylglyceride, and four carbohydrates (glucose, fructose, sucrose, and trehalose), as well as decreased ovarian cell mitosis, increased ovarian cell apoptosis, and downregulation of the JH receptor Met and its early-responsive gene Kr-h1. Together, these data suggest that LsFAMeT- and LsJHAMT-mediated JH biosynthesis regulates the reproductive capabilities of SBPH through energy mobilization, and ovarian cell activity. Our findings help elucidate the role of JH in insect reproduction and provide insights into key enzymes that may serve as potential targets for the development of selective insect growth regulators.