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Title: Eicosanoid signaling in insects: from discovery to plant protection

item Stanley, David
item KIM, YONGGYUN - Andong National University

Submitted to: Critical Reviews in Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2013
Publication Date: 1/30/2014
Citation: Stanley, D.W., Kim, Y. 2014. Eicosanoid signaling in insects: from discovery to plant protection. Critical Reviews in Plant Sciences. 33(1):20-63.

Interpretive Summary: The concept of biological control of insects is based on the idea that direct application of insect predators, pathogens and parasites can reduce pest insect populations and their associated economic damage to crops. The problem, however, is the efficiency of these organisms in biological control programs is limited by insect immune defense reactions to challenge. One approach to improving the efficiency of biocontrol agents would be to somehow disable insect immune reactions to viral, bacterial, fungal and parasitic infections. We have discovered one group of molecules that mediate insect immune reactions. In this paper we present a background description of insect immunity and discuss the roles of the molecules we discovered in mediating insect immune reactions to infection. In doing so, we join two separate concepts in insect science: one is research designed to understand how chemical mediators act in cellular immunity. The other is research designed to understand how molecular tools can be deployed to disable insect immunity. This new conjunction will be directly useful to scientists who are working to improve the efficacy of biological control methods. The ensuing improved biological control methods enhance long-term environmental and agricultural sustainability. These enhancements will benefit agricultural producers and all people who consume their products.

Technical Abstract: Prostaglandins (PGs) and related eicosanoids are signal moieties derived from arachidonic acid and two other C20 polyunsaturated fatty acids. They were discovered in the 1930s in the context of mammalian reproductive physiology; PGs were associated with the prostate gland, hence their name, and they stimulate uterine smooth muscle contraction. Determining PG chemical structures in the early 1960s and demonstrating that they mediate many human pathophysiological events in the 1970s stimulated intensive research over the following decades in universities, governments and the private sector. Interest in the biological significance of PGs in insects arose in the l970s and 1980s, which opened a new research frontier. PGs act in reproduction, releasing egg-laying behaviors in some species and signaling egg-maturation events in the Drosophila and silk moth models. They act in insect immunity, mediating and coordinating cellular and humoral responses to wounds, infection and invasion. PGs act in ion transport physiology in insect Malpighian tubules and recta. These compounds also mediate physiological trade-offs between insect immunity and reproduction. Finally, they are central players in the molecular ecology of interactions between blood-feeding insects and their vertebrate hosts. Some PG functions are critical at specific crucial moments in insect lives, moments we consider ‘emergencies’, such as the immediate reactions to infection. Certain microbial species have keyed into insect PG signaling and they evolved mechanisms to disable insect immune reactions to infection by inhibiting key enzymes in PG biosynthesis. We provide proof-of-principle that RNA interference treatments designed to silence genes in PG signaling disrupts insect immunity. In this review we describe the history, chemistry and biology of PGs. We use this background to argue that because PGs and other eicosanoids act in emergency situations, they are visible targets for development and deployment of novel insect pest management technologies. We expect these and other new technologies will be critical elements of long-term food security programs.