Department of Entomology, Pennsylvania State University, University Park, PA, USA.
Huck Institute of the Life Sciences, Pennsylvania State University, University Park, PA, USA.
J Chem Ecol. 2019 Jul;45(7):598-609. doi: 10.1007/s10886-019-01079-z. Epub 2019 Jun 20.
Insect herbivory induces plant defense responses that are often modulated by components in insect saliva, oral secretions or regurgitant, frass, or oviposition fluids. These secretions contain proteins and small molecules that act as elicitors or effectors of plant defenses. Several non-protein elicitors have been identified from insect oral secretions, whereas studies of insect saliva have focused mainly on protein identification. Yet, insect saliva may also contain non-protein molecules that could activate defense responses in plants. The goal of this study was to identify non-protein plant defense elicitors present in insect saliva. We used the fall armyworm (FAW), Spodoptera frugiperda and its host plants tomato, maize, and rice as a model system. We tested the effect of protein-digested saliva or non-protein components on herbivore-induced defense responses in maize, rice and tomato. We identified phytohormones in FAW saliva using high performance liquid chromatography coupled with mass spectrometry. The results of this study show that non-protein components in FAW saliva modulated defense responses in different plant species. The saliva of this insect contains benzoic acid, and the phytohormones jasmonic acid, salicylic acid, and abscisic acid at concentrations of <5 ng per μl of saliva. Plant treatment with similar phytohormone quantities detected in FAW saliva upregulated the expression of a maize proteinase inhibitor gene in maize, and down-regulated late herbivore-induced defenses in tomato plants. We conclude that FAW saliva is a complex fluid that, in addition to known enzymatic plant defense elicitors, contains phytohormones and other small molecules.
昆虫取食会诱导植物防御反应，而这些反应通常会受到昆虫唾液、口腔分泌物或反刍物、粪便或产卵液中的成分的调节。这些分泌物包含作为植物防御的激发子或效应子的蛋白质和小分子。已经从昆虫口腔分泌物中鉴定出几种非蛋白激发子，而昆虫唾液的研究主要集中在蛋白质鉴定上。然而，昆虫唾液中可能还含有能够激活植物防御反应的非蛋白分子。本研究的目的是鉴定昆虫唾液中存在的非蛋白植物防御激发子。我们使用秋粘虫（FAW）和其宿主植物番茄、玉米和水稻作为模型系统。我们测试了蛋白消化后的唾液或非蛋白成分对玉米、水稻和番茄中取食诱导的防御反应的影响。我们使用高效液相色谱-质谱联用技术鉴定了 FAW 唾液中的植物激素。本研究的结果表明，FAW 唾液中的非蛋白成分调节了不同植物物种的防御反应。这种昆虫的唾液中含有苯甲酸，以及浓度低于 5ng/μl 唾液的茉莉酸、水杨酸和脱落酸等植物激素。用 FAW 唾液中检测到的类似植物激素处理植物，上调了玉米中蛋白酶抑制剂基因的表达，并下调了番茄植物中晚期取食诱导的防御反应。我们得出结论，FAW 唾液是一种复杂的流体，除了已知的酶类植物防御激发子外，还含有植物激素和其他小分子。
