Data_Sheet_1_Hijacking the Mustard-Oil Bomb: How a Glucosinolate-Sequestering Flea Beetle Copes With Plant Myrosinases.pdf

Myrosinase enzymes play a key role in the chemical defense of plants of the order Brassicales. Upon herbivory, myrosinases hydrolyze the β-S-linked glucose moiety of glucosinolates, the characteristic secondary metabolites of brassicaceous plants, which leads to the formation of different toxic hydrolysis products. The specialist flea beetle, Phyllotreta armoraciae, is capable of accumulating high levels of glucosinolates in the body and can thus at least partially avoid plant myrosinase activity. In feeding experiments with the myrosinase-deficient Arabidopsis thaliana tgg1 × tgg2 (tgg) mutant and the corresponding Arabidopsis Col-0 wild type, we investigated the influence of plant myrosinase activity on the metabolic fate of ingested glucosinolates in adult P. armoraciae beetles. Arabidopsis myrosinases hydrolyzed a fraction of ingested glucosinolates and thereby reduced the glucosinolate sequestration rate by up to 50% in adult beetles. These results show that P. armoraciae cannot fully prevent glucosinolate hydrolysis; however, the exposure of adult beetles to glucosinolate hydrolysis products had no impact on the beetle’s energy budget under our experimental conditions. To understand how P. armoraciae can partially prevent glucosinolate hydrolysis, we analyzed the short-term fate of ingested glucosinolates and found them to be rapidly absorbed from the gut. In addition, we determined the fate of ingested Arabidopsis myrosinase enzymes in P. armoraciae. Although we detected Arabidopsis myrosinase protein in the feces, we found only traces of myrosinase activity, suggesting that P. armoraciae can inactivate plant myrosinases in the gut. Based on our findings, we propose that the ability to tolerate plant myrosinase activity and a fast glucosinolate uptake mechanism represent key adaptations of P. armoraciae to their brassicaceous host plants.

黑芥子酶（myrosinase）在十字花目（Brassicales）植物的化学防御中发挥关键作用。当遭受植食性昆虫取食时，黑芥子酶可水解十字花科植物特征性次生代谢物硫代葡萄糖苷（glucosinolates）的β-S连接葡萄糖基团，进而生成多种毒性水解产物。专食性跳甲芝麻跳甲（Phyllotreta armoraciae）能够在体内富集高浓度的硫代葡萄糖苷，从而可部分规避植物黑芥子酶的防御活性。本研究利用黑芥子酶缺陷型拟南芥（Arabidopsis thaliana）tgg1×tgg2（tgg）突变体及其对应的Col-0野生型拟南芥开展取食实验，探究了植物黑芥子酶活性对成年芝麻跳甲体内摄入的硫代葡萄糖苷代谢归趋的影响。实验结果显示，拟南芥黑芥子酶可水解部分摄入的硫代葡萄糖苷，进而使成年跳甲的硫代葡萄糖苷储积率降低至多50%。该结果表明，芝麻跳甲无法完全阻止硫代葡萄糖苷的水解；但在本实验条件下，成年跳甲暴露于硫代葡萄糖苷水解产物并不会对其能量预算产生影响。为解析芝麻跳甲如何能够部分阻止硫代葡萄糖苷水解，我们分析了摄入的硫代葡萄糖苷的短期归趋，发现其可从肠道快速被吸收。此外，我们还检测了芝麻跳甲体内摄入的拟南芥黑芥子酶的归趋：尽管在粪便中检测到了拟南芥黑芥子酶蛋白，但仅发现极微量的黑芥子酶活性，这表明芝麻跳甲可在肠道中灭活植物来源的黑芥子酶。基于上述研究结果，我们提出：耐受植物黑芥子酶活性的能力以及快速的硫代葡萄糖苷摄取机制，是芝麻跳甲适应其十字花科寄主植物的关键适应性特征。