Hubei Engineering Technology Center for Forewarning and Management of Agricultural and Forestry Pests, College of Agriculture, College of Life Sciences, Yangtze University, Jingzhou, Hubei Province, China.
Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests, Guangxi Academy of Agricultural Sciences, Nanning, Guangxi Province, China.
Insect Mol Biol. 2024 Aug;33(4):417-426. doi: 10.1111/imb.12909. Epub 2024 Mar 28.
REPAT (response to pathogen) is an immune-associated gene family that plays important roles in insect immune response to pathogens. Although nine REPAT genes have been identified in Spodoptera frugiperda (Lepidoptera: Noctuidae) currently, their functions and mechanisms in the immune response to pathogens still remain unclear. Therefore, SfREPAT38, a pathogen response gene (REPAT) of S. frugiperda, was characterised and its function was analysed. The results showed that SfREPAT38 contains a signal peptide and a transcription activator MBF2 (multi-protein bridging factor 2) domain. Quantitative real-time polymerase chain reaction analysis showed that SfREPAT38 was highly expressed in the sixth-instar larvae (L6) and was the highest in expression in the midgut of L6. We found that the expression of SfREPAT38 could be activated by challenge with four microbial pathogens (Bacillus thuringiensis, Metarhizium anisopliae, Spodoptera exigua nuclearpolyhedrosis and Escherichia coli), except 12 h after E. coli infection. Furthermore, the SfREPAT38 expression levels significantly decreased at 24, 48 and 72 h after SfREPAT38 dsRNA injection or feeding. Feeding with SfREPAT38 dsRNA significantly decreased the weight gain of S. frugiperda, and continuous feeding led to the death of S. frugiperda larvae from the fourth day. Moreover, SfREPAT38 dsRNA injection resulted in a significant decrease of weight gain on the fifth day. Silencing SfREPAT38 gene down-regulated the expression levels of immune genes belonging to the Toll pathway, including SPZ, Myd88, DIF, Cactus, Pell and Toll18W. After treatment with SfREPAT38 dsRNA, S. frugiperda became extremely sensitive to the B. thuringiensis infection, and the survival rate dramatically increased, with 100% mortality by the eighth day. The weight of S. frugiperda larvae was also significantly lower than that of the control groups from the second day onwards. In addition, the genes involved in the Toll signalling pathway and a few antibacterial peptide related genes were down-regulated after treatment. These results showed that SfREPAT38 is involved in the immune response of S. frugiperda larvae through mediating Toll signalling pathway.
REPAT（对病原体的反应）是一个与免疫相关的基因家族，在昆虫对病原体的免疫反应中发挥着重要作用。尽管目前已在草地贪夜蛾（鳞翅目：夜蛾科）中鉴定出 9 个 REPAT 基因，但它们在对病原体的免疫反应中的功能和机制仍不清楚。因此，本研究对草地贪夜蛾的一个病原体反应基因（REPAT）SfREPAT38 进行了鉴定，并分析了其功能。结果表明，SfREPAT38 含有一个信号肽和一个转录激活因子 MBF2（多蛋白桥接因子 2）结构域。定量实时聚合酶链反应分析表明，SfREPAT38 在 6 龄幼虫（L6）中高表达，在 L6 中肠中的表达最高。我们发现，SfREPAT38 的表达可被四种微生物病原体（苏云金芽孢杆菌、金龟子绿僵菌、斜纹夜蛾核型多角体病毒和大肠杆菌）的挑战激活，但在大肠杆菌感染后 12 小时除外。此外，在 SfREPAT38 dsRNA 注射或喂食后 24、48 和 72 小时，SfREPAT38 的表达水平显著下降。喂食 SfREPAT38 dsRNA 显著降低了草地贪夜蛾的体重增加，连续喂食导致第四天草地贪夜蛾幼虫死亡。此外，SfREPAT38 dsRNA 注射导致第五天体重增加显著下降。沉默 SfREPAT38 基因下调了属于 Toll 途径的免疫基因的表达水平，包括 SPZ、Myd88、DIF、Cactus、Pell 和 Toll18W。用 SfREPAT38 dsRNA 处理后，草地贪夜蛾对苏云金芽孢杆菌的感染变得极其敏感，存活率显著增加，到第 8 天死亡率达到 100%。从第二天开始，SfREPAT38 幼虫的体重也明显低于对照组。此外，处理后 Toll 信号通路相关基因和少数抗菌肽相关基因的表达也下调。这些结果表明，SfREPAT38 通过介导 Toll 信号通路参与草地贪夜蛾幼虫的免疫反应。
