Plants deploy an arsenal of chemical and physical defenses against arthropod herbivores, but it may be most cost efficient to produce these only when attacked. Herbivory activates complex signaling pathways involving several phytohormones, including jasmonic acid (JA), which regulate production of defensive compounds. The Poaceae also have the capacity to take up large amounts of silicon (Si) which accumulates in plant tissues. Si accumulation has anti-herbivore properties, but it is poorly understood how Si defenses relate to defense hormone signaling. Here we show that Si enrichment causes the model grass Brachypodium distachyon to show lower levels of JA induction when attacked by chewing herbivores. Triggering this hormone even at lower concentrations, however, prompts Si uptake and physical defenses (e.g. leaf hairs) which negatively impact chewing herbivores. Removal of leaf hairs restored performance. Crucially, activation of such Si-based defense is herbivore-specific and occurred only in response to chewing and not fluid-feeding (aphid) herbivores. This aligned with our meta-analysis of 88 studies that showed Si defenses were more effective against chewing herbivores than fluid-feeders. Our results suggest integration between herbivore defenses in a model Si-accumulating plant, which potentially allows it to avoid unnecessary activation of other costly defenses.

中文翻译：

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有针对性的植物防御：硅保存影响咀嚼但不影响喂食食草动物的激素防御信号

植物对节肢动物食草动物部署了一系列化学和物理防御措施，但仅在受到攻击时生产这些防御措施可能最具成本效益。Herbivory 激活复杂的信号通路，涉及多种植物激素，包括茉莉酸 (JA)，可调节防御性化合物的产生。禾本科还具有吸收大量积累在植物组织中的硅 (Si) 的能力。Si 积累具有抗食草动物的特性，但人们对 Si 防御与防御激素信号传导的关系知之甚少。在这里，我们表明，当被咀嚼的食草动物攻击时，Si 富集导致模型草 Brachypodium distachyon 显示出较低水平的 JA 诱导。然而，即使在较低浓度下也能触发这种激素，会促进 Si 吸收和物理防御（例如 叶毛）对咀嚼食草动物产生负面影响。去除叶毛恢复了性能。至关重要的是，这种基于硅的防御的激活是草食动物特有的，并且仅在对咀嚼而不是液体喂养（蚜虫）食草动物的反应中发生。这与我们对 88 项研究的荟萃分析一致，这些研究表明硅防御对咀嚼食草动物比液体喂食动物更有效。我们的结果表明，在模型积累硅的植物中，食草动物防御之间的整合，这可能使其避免不必要地激活其他昂贵的防御。这与我们对 88 项研究的荟萃分析一致，这些研究表明硅防御对咀嚼食草动物比液体喂食动物更有效。我们的结果表明，在模型积累硅的植物中，食草动物防御之间的整合，这可能使其避免不必要地激活其他昂贵的防御。这与我们对 88 项研究的荟萃分析一致，这些研究表明硅防御对咀嚼食草动物比液体喂食动物更有效。我们的结果表明，在模型积累硅的植物中食草动物防御之间的整合，这可能使其避免不必要地激活其他昂贵的防御。