Wang K, Züst T
Department of Systematic and Evolutionary Botany, University of Zürich, Zürich, Switzerland.
Plant Biol (Stuttg). 2025 Aug;27(5):861-872. doi: 10.1111/plb.13777. Epub 2025 Feb 12.
Plants invest a substantial fraction of their resources into defence against herbivores, with the highest levels of defence often allocated only to the most valuable tissues. Plants in the genus Erysimum (Brassicaceae) have evolved the ability to produce novel cardenolides, in addition to ancestrally conserved glucosinolates. While these plants co-express both defences, differences in tissue-specific expression might represent an effective cost-saving strategy. Larvae of the glucosinolate-resistant diamondback moth Plutella xylostella occasionally feed on Erysimum cheiranthoides but tend to avoid younger leaves. Here, we predict that caterpillar feeding preference is shaped by variations in cardenolide levels. Thus, we quantified within-plant variations in defence and nutritional traits of vegetative or early reproductive plants and performed feeding assays to evaluate the relative importance of cardenolides. In accordance with optimal defence theory (ODT), the youngest leaves contained the most nutrients and had highest levels of cardenolides, glucosinolates and trichomes, with more extreme within-plant differences found in reproductive plants. Caterpillars consistently avoided the well-defended youngest leaves, both on whole plants and detached leaf discs. Surprisingly, neither experimental addition (external application) nor removal (CRISPR-Cas9 knockout) of cardenolides significantly affected caterpillar feeding preference. Physical and chemical defences, including cardenolides, co-vary within E. cheiranthoides to maximize defence of youngest leaves. While P. xylostella clearly responds to some of these traits, the prominent cardenolide defence appears to lack potency against this specialist herbivore. Nonetheless, the careful regulation and re-mobilization of cardenolides to younger leaves during plant development suggests an important role in plant functioning.
植物会将大量资源投入到抵御食草动物的防御机制中，其中最高水平的防御通常仅分配给最有价值的组织。糖芥属（十字花科）植物除了具有祖传保守的芥子油苷外，还进化出了产生新型强心苷的能力。虽然这些植物同时表达两种防御机制，但组织特异性表达的差异可能代表了一种有效的节省成本策略。对芥子油苷具有抗性的小菜蛾幼虫偶尔会取食小花糖芥，但往往会避开较嫩的叶片。在这里，我们预测毛虫的取食偏好是由强心苷水平的变化所塑造的。因此，我们对营养期或早期生殖期植物的防御和营养性状的植株内变异进行了量化，并进行了取食试验，以评估强心苷的相对重要性。根据最佳防御理论（ODT），最嫩的叶片含有最多的营养物质，并且强心苷、芥子油苷和毛状体的含量最高，在生殖期植物中发现的植株内差异更为显著。毛虫在整株植物和离体叶片上都始终避开防御良好的最嫩叶片。令人惊讶的是，无论是强心苷的实验添加（外部施用）还是去除（CRISPR-Cas9基因敲除）都没有显著影响毛虫的取食偏好。包括强心苷在内的物理和化学防御在小花糖芥植株内共同变化，以最大限度地保护最嫩叶片。虽然小菜蛾对其中一些性状有明显反应，但突出的强心苷防御似乎对这种专食性食草动物缺乏效力。尽管如此，在植物发育过程中对强心苷进行精细调控并将其重新转运到较嫩叶片中，这表明其在植物功能中发挥着重要作用。
