Rahfeld Peter, Haeger Wiebke, Kirsch Roy, Pauls Gerhard, Becker Tobias, Schulze Eva, Wielsch Natalie, Wang Ding, Groth Marco, Brandt Wolfgang, Boland Wilhelm, Burse Antje
Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, Jena, Germany.
Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, Jena, Germany; Department of Entomology, Max Planck Institute for Chemical Ecology, Jena, Germany.
Insect Biochem Mol Biol. 2015 Mar;58:28-38. doi: 10.1016/j.ibmb.2015.01.003. Epub 2015 Jan 14.
Plant-feeding insects are spread across the entire plant kingdom. Because they chew externally on leaves, leaf beetle of the subtribe Chrysomelina sensu stricto are constantly exposed to life-threatening predators and parasitoids. To counter these pressures, the juveniles repel their enemies by displaying glandular secretions that contain defensive compounds. These repellents can be produced either de novo (iridoids) or by using plant-derived precursors. The autonomous production of iridoids pre-dates the evolution of phytochemical-based defense strategies. Both strategies include hydrolysis of the secreted non-toxic glycosides in the defensive exudates. By combining in vitro as well as in vivo experiments, we show that iridoid de novo producing as well as sequestering species rely on secreted β-glucosidases to cleave the pre-toxins. Our phylogenetic analyses support a common origin of chrysomeline β-glucosidases. The kinetic parameters of these β-glucosidases demonstrated substrate selectivity which reflects the adaptation of Chrysomelina sensu stricto to the chemistry of their hosts during the course of evolution. However, the functional studies also showed that the broad substrate selectivity allows building a chemical defense, which is dependent on the host plant, but does not lead to an "evolutionary dead end".
以植物为食的昆虫遍布整个植物王国。由于叶甲亚族（狭义的叶甲亚族）的叶甲在叶片外部咀嚼，它们不断面临危及生命的捕食者和寄生生物。为了应对这些压力，幼虫通过分泌含有防御性化合物的腺体分泌物来驱赶敌人。这些驱避剂既可以从头合成（环烯醚萜），也可以利用植物衍生的前体物质来产生。环烯醚萜的自主合成早于基于植物化学物质的防御策略的进化。这两种策略都包括对防御性分泌物中分泌的无毒糖苷进行水解。通过结合体外和体内实验，我们表明从头合成环烯醚萜以及积累环烯醚萜的物种都依赖分泌的β-葡萄糖苷酶来切割前毒素。我们的系统发育分析支持叶甲亚族β-葡萄糖苷酶有共同的起源。这些β-葡萄糖苷酶的动力学参数显示出底物选择性，这反映了狭义叶甲亚族在进化过程中对其宿主化学性质的适应。然而，功能研究还表明，广泛的底物选择性有助于建立一种依赖于宿主植物的化学防御，但不会导致“进化死胡同”。
