Collaborative Research: Integrative Approaches to Plant Cell Wall Digestion by Non holometabolous Insects

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Plant cell walls contain lignocellulosic compounds that are difficult to degrade, such as xylan, cellulose, hemicellulose, and pectin. However, insect herbivores are capable of degrading these compounds and using the simpler compounds derived from the degradation processes for energy. While early work assumed that the source of the catalyst enzymes involved in the biochemical breakdown of lignocellulosic compounds (i.e., plant cell wall degradation enzymes, PCWDE) in insects was gut-resident symbiotic bacteria, recent work has shown that PCWDE produced by the cells of the insect gut are more important than previously realized. The goal of this research is to examine the diversity of PCWDE in two major lower insect lineages using a combination of functional genomics and biochemical tests. This basic research will improve understanding about the physiological mechanisms of insect digestion and may yield novel insights about insect control methods, biofuel industry improvements, and other industrial applications. This work will provide the opportunity for undergraduate, high school and graduate students to gain experience in cutting edge functional genomics, and insect physiology and biochemistry. Museum exhibits will be produced to educate the public about the importance of wood feeding insects. These exhibits will be presented at the University of California David Bohart Museum of Entomology and several other science museums across California and Tennessee. Preliminary work revealed that Phasmids (walking sticks) and Thysanurans (silverfish and firebrats) have strikingly high numbers of PCWDE, that these genes show compartment specific expression within the gut, and are effective at degrading plant cell wall compounds. This project will identify the full complement of PCWDE present in the focal species (6 Phasmids and 3 Thysanurans) and compare the activity and expression levels of them in the digestive systems of these insects. Using heterologous expression, the researchers will characterize the activity of the most active enzymes in these systems. The researchers will also analyze how patterns of gene expression correlate with the physical attributes of the gut, which vary greatly between the two focal insect orders. The ultimate goal is to describe the variation in physiological compartmentalization of the digestive system and determine how it works synergistically with a diversity of differentially-expressed enzymes to maximize digestion of lignocellulosic compounds. Findings from this research will be published in peer-reviewed journals, and presented at regional and national scientific meetings.