State Key Laboratory for Ecological Pest Control of Fujian and Taiwan Crops, Institute of Applied Ecology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China; International Joint Research Laboratory of Ecological Pest Control, Ministry of Education, Fujian Agriculture and Forestry University, Fuzhou, 350002, China; Ministerial and Provincial Joint Innovation Centre for Safety Production of Cross-Strait Crops, Fujian Agriculture and Forestry University, Fuzhou, 350002, China; Key Laboratory of Integrated Pest Management for Fujian-Taiwan Crops, Ministry of Agriculture and Rural Affairs, Fuzhou, 350002, China.
School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, 300072, China.
Dev Comp Immunol. 2023 Sep;146:104737. doi: 10.1016/j.dci.2023.104737. Epub 2023 May 24.
Melanization is a component of the humoral immune defense of insects and is induced by serine protease-mediated phenoloxidase (PO) catalysis. Prophenoloxidase (PPO) in the midgut of Plutella xylostella is activated by the CLIP domain serine protease (clip-SP) in response to Bacillus thuringiensis (Bt) infection, but the detailed signaling cascade following this activation is unknown. Here, we report that activation of clip-SP enhances PO activity in the P. xylostella midgut by cleaving three downstream PPO-activating proteases (PAPs). First, the expression level of clip-SP1 was increased in the midgut after Bt8010 infection of P. xylostella. Then, purified recombinant clip-SP1 was able to activate three PAPs - PAPa, PAPb and PAP3 - which in turn enhanced their PO activity in the hemolymph. Furthermore, clip-SP1 showed a dominant effect on PO activity compared to the individual PAPs. Our results indicate that Bt infection induces the expression of clip-SP1, which is upstream of a signaling cascade, to efficiently activate PO catalysis and mediate melanization in the midgut of P. xylostella. And it provides a basis for studying the complex PPO regulatory system in the midgut during Bt infection.
黑化是昆虫体液免疫防御的一个组成部分，是由丝氨酸蛋白酶介导的酚氧化酶（PO）催化诱导的。小菜蛾中肠的原酚氧化酶（PPO）在苏云金芽孢杆菌（Bt）感染时被 CLIP 结构域丝氨酸蛋白酶（clip-SP）激活，但激活后的详细信号级联尚不清楚。在这里，我们报告说，clip-SP 的激活通过切割三个下游的 PPO 激活蛋白酶（PAPs），增强了小菜蛾中肠的 PO 活性。首先，在小菜蛾感染 Bt8010 后，中肠中 clip-SP1 的表达水平增加。然后，纯化的重组 clip-SP1 能够激活三个 PAPs-PAPA、PAPb 和 PAP3-它们反过来又增强了它们在血淋巴中的 PO 活性。此外，与单个 PAP 相比，clip-SP1 对 PO 活性表现出优势效应。我们的结果表明，Bt 感染诱导了信号级联上游的 clip-SP1 的表达，从而有效地激活了 PO 催化，并介导了小菜蛾中肠的黑化。这为研究 Bt 感染期间中肠中复杂的 PPO 调节系统提供了依据。
