Abstract The NF‐ κ B transcription factor Relish and Cap “n” collar (Cnc) transcription factor CncC primarily regulate innate immune defense and xenobiotic response, respectively, in insects. However, the roles of Relish and CncC in insect development as well as their mutual regulation are still poorly understood. In this study, Relish was cloned from Tribolium castaneum . Spatial‐temporal expression analysis revealed that TcRelish expression was highly expressed in the fat body and in 7‐d‐old female pupae, respectively. Knockdown of TcRelish in 15‐d‐old larvae resulted in failure of 95% of larvae to pupate, remaining in the larval stage until death. Mechanistically, ds TcRelish treatment led to an increase of juvenile hormone (JH) content by 30.66% concomitant with the upregulation of JH receptor gene Met and JH‐responsive gene Kr‐h1 by 94.16% and 57.93%, respectively. Notably, knockdown of TcRelish downregulated the expression of JH degradation enzyme genes JHEH2 , JHEH3 , and JHEH4 by 29.76%, 22.44%, and 23.83%, respectively. Similarly, knockdown of TcCncC resulted in failure of larval pupation, an increase of JH content, upregulation of Met and Kr‐h1 as well as downregulation of JHEH2 , JHEH3 , and JHEH4 . Further analysis revealed that the protein level of TcCncC was significantly reduced in 6 d after TcRelish RNAi, whereas stimulation with the Relish agonist NF‐ κ B activator 2 significantly upregulated TcCncC protein levels. Additionally, a luciferase reporter assay revealed that overexpression of TcRelish significantly enhanced the promoter activity of TcCncC by 5.78 fold. These results demonstrate that TcRelish directly regulates larval development through transcriptional regulation of TcCncC , thereby altering the metabolism of JH.
Li et al. (2026) studied this question.