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

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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.