The KNRL nuclear receptor controls hydrolase‐mediated vitellin breakdown during embryogenesis in the brown planthopper, Nilaparvata lugens

Abstract

Vitellin (Vn) homeostasis is central to the fecundity of oviparous insects. Most studies have focused on the synthesis and transportation of Vn as a building block for developing eggs during vitellogenesis; however, less is known about how the utilization of this nutrient reserve affects embryonic development. Here, we show that the single ortholog of the knirps and knirps-like nuclear receptors, KNRL, negatively regulates Vn breakdown by suppressing the expression of hydrolase genes in the brown planthopper, Nilaparvata lugens. KNRL was highly expressed in the ovary of adult females, and knockdown of KNRL by RNA interference resulted in the acceleration of Vn breakdown and the inhibition of embryonic development. Transcriptome sequencing analysis revealed that numerous hydrolase genes, including cathepsins and trypsins were up-regulated after KNRL knockdown. At least eight of the nine significantly enriched Gene Ontology terms for the up-regulated genes were in proteolysis-related categories. The expression levels of five selected trypsin genes and the enzymatic activities of trypsin in the embryos were significantly increased after KNRL knockdown. Moreover, trypsin injection prolonged egg duration, delayed embryonic development, accelerated Vn breakdown and severely reduced egg hatchability, a pattern similar to that observed in KNRL-silenced N. lugens. These observations suggest that KNRL controls Vn breakdown in embryos via the transcriptional inhibition of hydrolases. Generally, this study provides a foundation for understanding how embryo nutrient reserves are mobilized during embryogenesis and identifies several genes and pathways that may prove valuable targets for pest control.

Inter-Alpha-Trypsin Inhibitor Heavy Chain 4 Plays an Important Role in the Development and Reproduction of Nilaparvata lugens

“…The Knirps-related nuclear receptor (KNRL) controls vitellin (Vn) breakdown in embryos via the transcriptional inhibition of hydrolases in N. lugens [ 38 ]. In previous work, the expression levels of five selected trypsin genes and the enzymatic activities of trypsin in embryos were found to be significantly increased after KNRL knockdown, and trypsin injection prolonged egg duration, delayed embryonic development, accelerated Vn breakdown, and severely reduced egg hatchability, a pattern similar to that observed in KNRL-silenced insects [ 38 ]. Thus it is also possible that silencing of Nl ITIH4 may increasingly affect Vg expression through an impact on trypsin activity.…”

Phytochemical Flavone Confers Broad-Spectrum Tolerance to Insecticides in Spodoptera litura by Activating ROS/CncC-Mediated Xenobiotic Detoxification Pathways

“…RNA samples prepared from S. litura larval midguts were sent to Novogene Co. Ltd. (Beijing, China) for Illumina sequencing as previously reported. , In brief, the purity and structural integrity of the extracted RNAs were verified with a Nanodrop One spectrophotometer (Life Technologies) and a Bioanalyzer 2100 system (Agilent Technologies, CA), respectively. Library construction was performed using the NEBNext Ultra RNA Library Prep Kit for Illumina (NEB) according to the manufacturer’s instruction.…”