The absence of juvenile hormone (JH) induces reproductive diapause in many insects. Downregulated JH biosynthesis is considered the critical factor that decreases the JH level. However, whether upregulated JH degradation could also contribute to JH deficiency and then induce reproductive diapause remains poorly known. In this work, we used the cabbage beetle, Colaphellus bowringi, as the model and investigated the function of JH degradation genes in reproductive diapause preparation via RNAi-mediated loss-of-function. Three JH degradation genes, including JH epoxide hydrolase 1 (JHEH1), JHEH2, and JH diol kinase (JHDK), were cloned, and the deduced proteins contained the conserved domains and motifs well-identified in the same proteins of other insects. JHEH1, JHEH2, and JHDK were all highly expressed in the diapause-destined (DD) females compared to the non-diapause-destined (NDD) females. Knocking down these JH degradation genes in DD females elevated JH signaling, indicated by increased expressions of JH-inducible genes and vitellogenin genes, but did not induce ovary development. Meanwhile, the knockdown of JH degradation genes significantly suppressed diapause-associated phenotypic traits, including fat storage, and the expression of genes related to fat storage and stress tolerance. A photoperiodic transfer experiment suggested that high expression of JHEH2 in DD female was preprogrammed by long day during the larval stage. Knockdown of JH signaling through Methoprene-tolerant and Krüppel homolog 1 induced high expression of JHEH2 in DD females. Considering that RNAi of JH degradation genes affected some diapause-related traits in DD females but failed to induce the non-diapause phenotype in full, we conclude that JH degradation pathways play limited regulatory roles in the reproductive diapause preparation of C. bowringi.

中文翻译：

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幼年激素降解途径在甘蓝甲虫Colaphellus bowringi的生殖滞育制备中的有限调节作用。

幼体激素（JH）的缺乏会引起许多昆虫的生殖滞育。JH生物合成的下调被认为是降低JH水平的关键因素。然而，尚不清楚JH降解的上调是否也可能导致JH缺乏，进而引起生殖性滞育。在这项工作中，我们使用甘蓝甲虫Colaphellus bowringi作为模型，并通过RNAi介导的功能丧失研究了JH降解基因在生殖滞育制备中的功能。克隆了三个JH降解基因，包括JH环氧水解酶1（JHEH1），JHEH2和JH二醇激酶（JHDK），并且推导的蛋白质包含在其他昆虫的相同蛋白质中可以很好识别的保守结构域和基序。JHEH1，JHEH2，与非滞后性（NDD）雌性相比，滞育性（DD）雌性和JHDK均高表达。降低DD雌性中的这些JH降解基因可提高JH信号传导，这可通过JH诱导基因和卵黄蛋白原基因的表达增加来表明，但并未诱导卵巢发育。同时，敲低JH降​​解基因显着抑制了滞育相关的表型性状，包括脂肪储存，以及与脂肪储存和压力耐受性相关的基因的表达。光周期转移实验表明，在幼虫期的漫长一天中，已预先编程了DD雌性中JHEH2的高表达。通过甲氧戊二烯耐受性和Krüppel同源物1抑制JH信号传导在DD雌性中诱导JHEH2高表达。