Mixed Messages in Caterpillar Saliva: Disruptive and Deceptive Signals for Plant Defenses

注射到脊椎动物宿主中的食血节肢动物的唾液中含有许多用于防止血液凝结的化合物，这些化合物对于躲避宿主的检测非常重要。尽管植物和动物都能对寄生虫产生不同的防御能力，而且与食血节肢动物形成鲜明对比，但人们对毛虫的唾液如何干扰宿主植物的防御反应知之甚少。该项目将通过观察毛虫唾液是否有助于逃避植物的防御，来确定毛虫唾液是否有助于逃避植物的防御：1)减弱毛虫摄取的宿主植物的酶防御，2)扰乱参与防御诱导的植物信号通路。实验旨在测试唾液和玉米穗虫中的主要唾液酶葡萄糖氧化酶影响植物中防御信号肽、系统素的运输和活性以及茉莉酸的生物合成的能力。众所周知，系统素和茉莉酸都能促进氧化酶的产生和抗虫性。唾液葡萄糖氧化酶诱导水杨酸产生的能力也将被测试，这是表达系统对植物病原体的获得性抗性、抑制茉莉酸合成以及随后的昆虫抗性所必需的。将使用几种毛虫-植物组合来测试这些机制的重要性。这些目标的完成将为比较以植物为食的节肢动物与以血液为食的节肢动物的适应情况提供一个概念框架。这些实验可能提供第一个证据，证明食草动物的唾液在抑制宿主的酶防御和扰乱植物用来抵抗食草动物攻击的防御信号通路中发挥作用。

Saliva of blood-feeding arthropods injected into their vertebrate hosts contains many chemical compounds used to prevent the clotting of blood, which are important in evading host detection. Although both plants and animals produce diverse defenses against their parasites, and in stark contrast to the blood feeding arthropods, very little is known about how the saliva of caterpillars interfere with host plant defense responses. This project will determine if caterpillar saliva assists in evasion of plant defenses by observing whether caterpillar saliva: 1) attenuates the enzymatic defenses of the host plant ingested by caterpillars, and 2) disrupts plant signaling pathways involved in defense induction. Experiments are designed to test the ability of saliva and the predominant salivary enzyme in the corn earworm, glucose oxidase, to affect transport and activity of the defense signal peptide, systemin, and biosynthesis of jasmonic acid in plants. Both systemin and jasmonic acid are known to mediate increased production of oxidative enzymes and insect resistance. The ability of salivary glucose oxidase to induce salicylic acid production, required for the expression of systemic acquired resistance against plant pathogens, inhibition of jasmonic acid synthesis, and subsequent insect resistance will also be tested. Several caterpillar-plant combinations will be used to test the importance of these mechanisms. Completion of these objectives will provide a conceptual framework for the comparison of adaptations plant-feeding arthropods use against their hosts to those of blood feeding arthropods. These experiments may furnish the first evidence that herbivore saliva plays a role in suppressing host enzymatic defenses and disrupting defense signal pathways used by plants to resist herbivore attack.