Gregg A. Howe Professor
- B.A. 1983, East Carolina University
- Ph.D. 1993, University of California, Los Angeles
- Postdoctoral Fellow, 1993-1997, Washington State University
- NIH Postdoctoral Fellow, 1994-1997
Lab Members
howeg@msu.edu
122 Plant Biology Lab
Michigan State University
East Lansing, MI 48824-1319
Office: 517-355-5159
Lab: 517-355-5197
Publication search:
Gregg A. Howe Research Interests continued
Plant Anti-Insect Proteins
A central question in plant-insect interaction research concerns the identity of JA-regulated compounds that thwart the ability of herbivores to colonize, consume, or reproduce on plants. Although plant secondary metabolites have traditionally been viewed as the major determinants of host plant utilization by insects, proteins are also an important component of the plant’s defensive response. Wound-inducible proteinase inhibitors that impair digestive proteases in the insect gut provide one of the best examples of a defensive protein whose synthesis is tightly regulated by the JA pathway.
We are using proteomic analysis of insect gut content and feces (frass) to identify the plant's defensive protein arsenal. This novel approach is based on the premise that defensive proteins are relatively resistant to gut proteases and, as a consequence, are highly enriched during passage of the food bolus through the insect (Fig. 2). Application of this procedure to tomato-reared M. sexta larvae led to the identification of JA-regulated isoforms of arginase and threonine deaminase, which degrade the essential amino acids arginine and threonine, respectively, in the caterpillar gut. We hypothesize that arginase and threonine deaminase are components of a multitiered defensive system that functions to deplete the availability of essential amino acids in the insect gut. With funding from the USDA, we are using this proteomics platform to systemically identify anti-insect proteins from a broad range of crop plants. Results obtained from this research are expected to provide new tools to improve pest tolerance in crop plants.
Figure 2. Plant-insect relationships are profoundly influenced by post-ingestive interactions between plant defensive chemicals and components of the insect digestive tract. In this photograph of the cabbage looper (Trichoplusia ni) feeding on Arabidopsis thaliana, ingested plant material is visible in the caterpillar’s green-colored gut. The Howe lab is using proteomics to identify plant proteins that are stable during passage through the insect digestive tract. Figure courtesy of Kurt Stepnitz (Michigan State University).
Glandular Trichomes in the Solanum
Glandular trichomes (GTs) populate the aerial surfaces of approximately 30% of all vascular plant species. These uni- and multi-cellular appendages play a critical role in plant protection against insects, and various abiotic stress conditions as well. A remarkable feature of GTs is their capacity to synthesize, store, and secrete large amounts of secondary metabolites. Because they are not essential for plant viability, GTs provide a unique opportunity to study complex and specialized metabolic pathways that operate within the confines of a simple and highly accessible developmental structure. Many GT-borne compounds have significant commercial value as pharmaceuticals, fragrances, food additives, and natural pesticides. For this reason, the prospect of exploiting GTs as “chemical factories” to produce high-value plant products has recently captured the attention of plant biochemists and biotechnologists alike.
Tomato and related species in the Solanum produce a variety of GT types on the surface of leaves, stems, and reproductive structures (Figure 3). The occurrence of multiple types of GTs within a single species provides a unique opportunity to understand the regulation of development of each class of trichome, and to identify the major biosynthetic pathways operating in each type. We are involved in a collaborative NSF-funded Plant Genome Project (http://www.trichome.msu.edu/) to study the morphogenesis, metabolic pathways, and function of GTs in cultivated tomato and its closely related wild species. The long-term goal of this collaborative project is to lay a foundation for a complete understanding of the network of genes and proteins involved in the development and metabolic function of GTs in Solanum spp. Work in our lab is currently focused on the characterization of several tomato mutants that are defective in GT development and metabolism. This line of investigation builds on our previous research showing that the JA/COI1 signaling pathway in tomato is required for the normal development and metabolic function of GTs.
Figure 3. Scanning electron micrograph of type VI glandular trichomes on the tomato leaf surface. Photograph courtesy of David Marks (University of Minnesota).