Research - Harold Rathburn
Presently I'm involved with three on-going research projects and another project is awaiting an interested graduate student:
(1) The first research project involves participation of undergraduate students entirely. I recruit those students that are majoring in biology who have an interest in research. These students get credit in Biology Problems (BIOL 4861).
Plants are known to produce chemicals that affect the growth of insects. In numerous instances, these naturally occurring chemicals have deleterious effects on the insects. Over the last 15 years or so, scientists have been working earnestly to identify plants that produce such compounds, to separate and isolate these toxic molecules, and to identify the exact molecular structure of these compounds.
A collaborative effort has been established with Dr. Manfred Reinecke (Dept of Chemistry, Texas Christian University) to address these goals. Our role at TSU is to assay insects against various plant extracts Dr. Reinecke's lab has prepared. The students prepare an artificial diet for lepidopteran insects, specifically Trichoplusia ni (cabbage looper). The students include in the diet extracts of different plants. After a specified period of time students weigh the larvae, analyze the data, and identify extracts that have toxic compounds. Students who have been involved in this project include Malinda Walter (Summer 1997), Tom Parish, (Summer 1998), Lori Acosta (Fall 2000), and Jana Caldwell (Spring 2002).
We have identified several plants that have toxic effects on insects. A search of the literature has revealed that many of these plants have not been previously identified as harboring molecules with insecticidal effects. A manuscript is in preparation.
(2) Another research project is funded by The Robert A. Welch Foundation through a Departmental Research Grant and involves undergraduate chemistry students via the course Chemistry Problems (CHEM 4861). Trypsin inhibitors are compounds produced by plants and are known to inhibit the growth of herbivorous insects. These compounds are found in large quantities in legumes. A native legume is our source of tissue for the isolation of this type of insecticidal molecule. Students work under my guidance to develop an isolation scheme to purify this molecule. After the molecule has been purified, students characterize its chemical and physical properties. Students Brian Kanz, Zachary House, Corrie Williams, Melissa Cather, and Lin Winton have worked on this project. This work was presented at the 34th Annual Meeting of the Dallas-Fort Worth Section of the American Chemical Society held at Tarleton State University in April, 2001.
(3) The third on-going research project has involved graduate and undergraduate students to identify drought resistant genes in crop plants that are agriculturally important to central Texas and native Texas plants. This project has been funded by the Amy Shelton McNutt Charitable Trust ($27,000) with matching funds from TSU, and recently by TSU's Organized Research Committee ($11,995). Jennifer Jurney, Nathan Leslie, Angela Roberson, Kashandra Smith, and Shyam Shridhar have all been involved in developing this project to its current status. By using the polymerase chain reaction (PCR), students have identified potential drought-tolerant genes in peanuts, little bluestem, side oats gramma, buffalo grass, and bermuda grass. A manuscript has been submitted to the Texas Journal of Science outlining our results with peanuts, and Mr. Shridhar has presented his results at the 105th Annual Meeting of the Texas Academy of Science, February 28-March 2, 2002. Mr. Shridhar gains graduate credit in Thesis (BIOL 5883).
(4) The last project is another approach to control insect pests and addresses a genetic question. Plants produce toxic proteins in response to pathogen attack. The gene that we use for this project is composed of three regions. One region is to direct the nascent protein to its proper cellular location, known as a leader sequence. The middle region codes for the toxic portion. The last region is hypothesized to neutralize the toxicity of the second region so the plant cell that translated it can survive. There is very little evidence to support this hypothesis.
One goal of this project is to express the various portions and combinations of this gene, purify the polypeptides, and inject them into insect larvae. This will determine which region(s) and combinations of the gene has the most toxicity towards insect pests, and if the hypothesized neutralizing region can render the toxic polypeptide non-toxic.
The next goal will then be to clone DNA sequences of the most toxic region(s) into a baculovirus. Baculoviruses infect only arthropods, almost entirely lepidopterans. These viruses can be used in an agricultural setting but they are slow to kill. By incorporating a toxic protein in the genome of the baculovirus the insect should be killed faster. There is some indication from other research groups and other toxic proteins that this approach can be successful. Hopefully, baculoviruses containing our selected gene will kill insects faster than wild-type baculoviruses.
This project has been supported by the TSU Organized Research Committee and has seen the graduation of Jeff Brady and Tony Reeves with Master's degrees. Both of them are now at Texas A&M University working on their PhD.