Genetic engineering of plants can reduce the need for chemical insecticides. This, in turn, can improve food safety, and reduce energy inputs and cost. In recent posts I described genetically engineering plants to produce their own pesticides, specifically TMOF and chitinase. I also discussed the effects that the pesticides created by those plants had on insect larvae. Savvy readers would have noticed that the effects on insects have been promising, but not stellar. It’s hard to get very enthusiastic about delayed weight gain as a measure of success!
That’s the reason the Rao research group at Università di Napoli took their project one step further and combined two biopesticides into a single plant. In a paper published in the 2010 Insect Biochemistry and Molecular Biology journal, these researchers tested the combination of plant-made TMOF and plant-made chitinase against larvae of the tobacco budworm.
Classical methods were used to breed genetically engineered (GE) plants producing TMOF with GE plants producing chitinase. The hybrid offspring produced both pesticidal proteins. Tobacco budworm (Heliothis virescens) larvae were fed leaves from the hybrid plants, or from GE plants producing either TMOF or chitinase, or from non-GE plants. The insects that were fed leaves from the TMOF-producing plants or the chitinase-producing plants developed more slowly than those fed with leaves from non-GE plants. But insects that were fed leaves from the dual-biopesticide plants developed even more slowly than the insects fed with leaves from plants producing either TMOF or chitinase alone. Most important for crop protection, approximately 75% of larvae fed on hybrid plants died. This suggests that GE plants producing both TMOF and chitinase protect themselves better against damage from insect larvae than plants producing only one of the proteins.
L Fiandra, I Terracciano, P Fanti, A Garonna, L Ferracane, V Fogliano, M Casartelli, B Giordana, R Rao and F Pennacchio. 2010. A viral chitinase enhances oral activity of TMOF. Insect Biochemistry and Molecular Biology 40: 533 – 540. DOI:10.1016/j.ibmb.2010.05.001
In a recent post, I mentioned the importance of identifying genes and proteins besides Bacillus thuringiensis (Bt) that can be used in the fight against crop pests. One such protein is chitinase.
Chitinase (pronounced ′kītən′ās) is an enzyme that breaks down the protein chitin. Chitin is an important component of insect exoskeletons and fungal cell walls. Functionally, it helps the insect or fungus retain its structure. Destroy the chitin, and the insect or fungus dies.
Scientists from the Rao laboratory at the University of Napoli hypothesized that a plant that made its own chitinase could protect itself against pests. They generated genetically engineered (GE) plants that produced chitinase, then tested the effect of the chitinase-producing GE plants on fungi and tobacco budworm larvae.
The results, published in a 2008 article in Transgenic Research, showed reduced fungal growth and abnormally slow weight gain in the insect larvae after they ingested the plants. This suggests that chitinase-producing GE plants protect themselves against damage from fungi and insect larvae better than non-GE plants.
In a future article, I will report on research which suggests that combining TMOF and chitinase improves crop protection against insect pests.
Corrado, G, Arciello, A, Fanti, P, Fiandra, L, Garonna, A, Diglio, MC, Lorito, M, Giordana, B, Pennacchio, F, Rao, R. 2008. The chitinase A from the baculovirus AcMNPV enhances resistance to both fungi and herbivorous pests in tobacco. Transgenic Research 17: 557 – 571, DOI: 10.1007/s11248-007-9129-4.
One reason for genetically engineered (GE) cotton’s dramatic and rapid acceptance by farmers is its improved control of three major insect pests: tobacco budworm, cotton bollworm and pink bollworm.
Cotton and other crop plants that are genetically engineered to make Bacillus
thuringensis (Bt) proteins become resistant to damaging crop pests (see Promising Results in the Fight Against Rice Stem Borer Moths). Unfortunately, as with any pesticide, insects develop tolerance to Bt over time, so it is important to investigate other proteins that might have efficacy as biopesticides. One such protein is Trypsin Modulating Oostatic Factor (TMOF).
TMOF is a protein that prevents insects from synthesizing the digestive enzyme trypsin, which is critical for digestion. TMOF was first developed for use on mosquitoes. Mosquito larvae that eat TMOF die because they cannot digest their food.
TMOF can have a similar effect on crop pests. In articles published in 2002 and 2003, a research group from the University of Napoli in Italy generated GE plants that produce TMOF. The researchers then tested the effect of the TMOF-producing GE plants on insect pests. Tobacco budworm larvae that ate leaves from these plants developed at an abnormally slow rate. Later studies, which I will cover in a future post, also showed that TMOF reduced the number of larvae that survive to adulthood. Taken together, these reports show that TMOF-producing GE plants protect themselves against damage from tobacco budworm.
Tortiglione C, Fanti P, Pennacchio F, Malva C, Breuer M, De Loof A, Monti L, Tremblay E, Rao R. The expression in tobacco plants of Aedes aegypti trypsin modulating oostatic factor (Aea-TMOF) alters growth and development of the tobacco budworm, Heliothis virescens. Molecular Breeding 2002; 9: 159 – 169. DOI: 10.1023/A:1019785914424.
Tortiglione C, Fogliano V, Ferracane R, Fanti P, Pennacchio F, Maria Monti L, Rao R. An insect peptide engineered into the tomato prosystemin gene is released in transgenic tabacco plants and exerts biological activity. Plant Molecular Biology 2003; 53: 891 – 902. DOI: 10.1023/B:PLAN.0000023667.62501.ef.
I also have researched the use of TMOF as a biopesticide, although not via GE plants. See one of my articles at Thompson DM, Young HP, Edens FW, Olmstead AW, LeBlanc GA, Hodgson E, Roe RM. Non-target toxicology of a new mosquito larvicide, trypsin modulating oostatic factor. Pesticide Biochemistry and Physiology 2004; 80: 131-142. DOI: 10.1016/j.pestbp.2004.06.009.
According to the USDA, over 430 million metric tons of rice were consumed worldwide in 2008, making it one of the world’s staple crops. But rice production has historically been threatened by disease and insect pests. Rice is Egypt’s second largest export crop. In Egypt, larvae of the rice stem borer moth (Chilo agamemnon) are major insect pests, which cause yield loss as high as 10 – 30%. Unfortunately, classical rice breeding has not improved resistance to this insect. Additionally, because the moth larva enters the rice stem, it is protected from most applied pesticides.
Since it’s difficult to externally apply the pesticide to the stem borer larvae, Egyptian genetic researcher Reda Moghaieb investigated the possibility of modifying the plant to make its own pesticide. Moghaieb chose a gene from a naturally occurring bacterium (Bacillus thuringiensis). This gene contains the instructions for producing a protein that is toxic to stem borer larvae. Moghaieb reasoned that when the gene was introduced into rice, the plant would produce the protein in cells of the stem, killing stem borer larvae that eat it. The gene was added to rice plants. When borer larvae were fed stems of these plants, the larvae died within four days; some died in only 24 hours. These results suggest that when the Bacillus thuringiensis gene is introduced into rice plants it acts as an effective pesticide against stem borer larvae.
REA Moghaieb. 2010. Transgenic rice plants expressing cry1Ia5 gene are resistant to stem borer (Chilo agamemnon). GM Crops 1:5, 1-6.
International Rice Research Institute has information about rice, its history, and its socio-economic relevance.