Progress 11/15/04 to 11/14/07
Outputs
OUTPUTS: The research completed during the grant period has been disseminated at a broad range of scientific meetings including invited talks at meetings for the Entomological Society of America, Insect Molecular Science Symposium, IOBC Conferences on Induced Plant Resistance, the American Society of Plant Biology, the American Chemical Society, and the Brazilian Chemical Ecology meeting (plenary address). Additionally invited talks have been given at several plant biology and entomology departments across the country. Students have also presented talks at the Entomological Society of America. The reearch has also been disseminated for high school students through our annual participation at the Penn State Science and Humanities Symposium. Following further analyses of protein data and EST database comparisons, several more publications will be submitted based upon the work completed in this proposal. Upon submission of these manuscripts several gene sequences will be deposited at
NCBI for general use by the scientific communities.
PARTICIPANTS: The following graduate students conducted a significant portion of their graduate research under the objectives of this proposal: Erica Schoemaker (M.S.) is focused on comparing the salivary secretions of lepidopteran larvae that utilize various feeding strategies, Donglan Tian (Ph.D.) is using a bioinformatics approach to identify new salivary genes from exisiting EST databases, Helene Quagebeur (Ph.D.) is comparing the role of omnivore feeding on induced defenses, Casey Delphia (Ph.D) focused on the role of caterpillar secretions in eliciting/suppressing indirect plant defenses and Wilma Aponte-Cordero (Ph.D.) is investigating jasmonate inducible defenses under field conditions. Ms. Aponte-Cordero also spent a 3 month research internship in the laboratory of Joop Van Loon of Waginengin University to study plant responses to herbivory. Janae Heath (undergraduate biology major, currently in medical school) identified new sources of caterpillar secretions from secondary
glands. Michelle Peiffer has been project assistant throughout the granting period and has focused on lab management, saliva collections, analysis of salivary gene expression and plant defense gene expression. Anthony Boughton (Postdoctoral Associate, currenly USDA-ARS employee) studied the induction of glandular trichomes in response to herbivory. The project also benefited from international collaborations with Eric Haubruge and Frederick Francis of Gembloux University who have assisted with the protoeomic analyses of caterpillar saliva and oral secretions.
TARGET AUDIENCES: We have participated in several efforts to provide science based knowledge to other groups. We annually participate in the Pennsylvania Junior Science & Humanities Symposium which provides a chance to educate high school students (and their intructors) on the science of entomology. We also participate in the WISER program which is a Penn State program focused on increasing the participation of women in science and engineering. Janae Heath completed a honor's thesis working in our laboratory.
PROJECT MODIFICATIONS: The major changes in the project including expanding the scope and the approach to testing the hypothesis that caterpillar saliva plays an important role in mediating plant defensive responses. First, because of the public availability of the Heliothis and Spodoptera EST databases have greatly expanded our ability to identify proteins from the proteomic work and to datamine for other likely salivary genes. Second, because the RNAi approach has not been fully adequate because it requires injection into the hemocoel(which has an unfortunate effect of inducing multiple salivary genes), we have alternatively used transient expression of salivary genes in tobacco to determine the effects of the proteins on plant defenses.
Impacts
The central hypothesis of the proposal is that salivary proteins play a significant role in mediating plant defense responses to herbivory. Our objectives were to characterize the secreted proteins of Helicoverpa zea, determine their function in plant defense signaling and determine how the host plant may affect the synthesis and secretion of these salivary proteins. We have identified 10 of 19 secreted proteins as determined by Mudpit and 2-D gel analyses. These proteins likely play a role in protection against microbes, detoxification of plant metabolites, and in suppression of host plant defenses (effectors). Furthermore we have also found more than 35 other salivary genes that likely encode for proteins that are secreted. Many of these salivary genes are impacted by the host plant in which the caterpillar has fed. We have conducted the most detailed analysis of the glucose oxidase and found that transient expression of the gene in tobacco downregulates the
production of alkaloids in the plant. Exciting recent data indicates that this salivary protein may play an additional role in detoxification of a broad array of plant secondary metabolites. We also have found that this salivary enzyme is more often found in caterpillar species with broad host ranges. Furthermore some of the salivary genes may encode proteins that as elicitors of plant defense. The overall findings of the project may yield several new avenuues or approaches for designing resistant plants. Plants expressing dsRNA that specifically target essential salivary genes may be a strategy for producing the next geenration of transgenic plants.
Publications
- Peiffer, M., and G. W. Felton. 2005. The host plant as a factor in the synthesis and secretion of salivary glucose oxidase in larval Helicoverpa zea. Arch. Insect Biochem. Physiol. 58:106-113.
- Musser, R. O., D. F. Cipollini, S. M. Hum-Musser, S. A. Williams, J. K. Brown, and G. W. Felton. 2005. Evidence that the caterpillar salivary enzyme glucose oxidase provides herbivore offense in solanaceous plants. Arch. Insect Biochem. Physiol. 58:128-137.
- Felton, G. W. 2005. Indigestion is a plant's best defense. Proceedings National Academy of Science 102:18771-18772.
- Boughton, A. J., K. Hoover, and G. W. Felton. 2005. Methyl jasmonate application induces increased densities of glandular trichomes on tomato, Lycopersicon esculentum. J. Chemical Ecology 31:2211-2216.
- Zhu-Salman, K., D. S. Luthe, and G. W. Felton. 2008. Arthropod-inducible proteins: broad spectrum defenses against multiple herbivores. Plant Physiology 146:1-7.
- Felton, G. W. 2008. Caterpillar secretions and induced plant responses. In A. Schaller, editor. Induce Plant Resistance to Herbivory. Springer Science, Berlin. Pages 369-387
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Progress 11/15/05 to 11/15/06
Outputs
We are investigating the role of salivary proteins of caterpillars in mediating plant defense responses to herbivory. We are characterizing secreted proteins of the cotton bollworm using a two-fol proteomics approach: 2D-gel electrophoresis/LC/MS/MS and by MUDPIT -LC/MS/MS. We have also identified small molecules in the saliva that include several plant hormones. The impact of these small molecules on expression of plant defense genes in the tomato plant is being investigated. We have also undertaken a comparative approach and are investigating saliva from 5 different caterpillar species to determine if there are specific mechanisms used by various species to avoid inducing plant responses.
Impacts
Induced resistance in plants is an environmentally and ecologically attractive strategy for use in controlling pest insect populations. Understanding how insects may circumvent induced resistance is an important step in effectively employing this biorational form of pest management. We are making significant progress in identifying the role of saliva in mediating induced resistance.
Publications
- Bede, J. C., Musser, R.O., Felton, G.W., and Korth, K.L. 2006. Caterpillar herbivory and saliva enzyme decrease transcript levels of Medicago truncatula genes encoding early enzymes in terpenoid biosynthesis. Plant Mol. Biol. 60:519-531.
- Musser, R.O., Farmer, E., Peiffer, M., and Felton, G.W. 2006. Ablation of caterpillar labial salivary glands: technique for determining the role of saliva in insect-plant interactions. J. Chem. Ecol. 32:981-992.
- Boughton, A. J., Hoover, K., and Felton, G.W. 2006. Impact of chemical elicitor applications on greenhouse tomato plants and populations of the green peach aphid, Myzus persicae. Entomol. Exp. Appl. 120: 175-188.
- Delphia, C.M., Mescher, M.C., Felton, G.W., and DeMoraes, C.M. 2006. Role of insect-derived cues in the elicitation of plant volatiles in tobacco, Nicotiana tabacum. Plant Signaling Behavior. 1:243-250.
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Progress 11/15/04 to 11/14/05
Outputs
We are investigating the role of salivary proteins in mediating plant defense responses to herbivory. We have characterized the secreted proteins of the cotton bollworm and identified ca. 25 proteins by LC/MS/MS analyses. Although many of these proteins no doubt play roles in mediating resistance to microbes (e.g., lysozyme) and aiding in digestion of food (e.g., proteases), a battery of the proteins may be important in modifying plant defensive responses. We have found that saliva suppresses scores of tomato plant defense genes that are regulated by the plant signal jasmonic acid. We are using RNA inference and other techniques to identify the principal components of saliva responsible for mediating these responses. We have also identified the induction of glandular trichomes (Type VI) in tomato as an important component of constitutive and induced resistance against caterpillars, aphids, and thrips. Wounding of plant tissue causes a massive increase in the number of
glandular trichomes formed on newly developing leaves. Again, the saliva of caterpillars is important in suppressing the induction of the trichomes. Experiments are underway to characterize the component(s) in saliva responsible for this suppression.
Impacts
Induced resistance in plants is an environmentally and ecologically attractive strategy for use in controlling pest insect populations. Understanding how insects may circumvent induced resistance is an important step in effectively employing this biorational form of pest management. We are making significant progress in identifying the mechanisms used by the cotton bollworm in circumventing induced resistance.
Publications
- Peiffer, M. and Felton, G. W. 2005. The host plant as a factor in the synthesis and secretion of salivary glucose oxidase in larval Helicoverpa zea. Arch Insect Biochem Physiol 58: 106-13.
- Boughton, A. J., Hoover, K. and Felton, G. W. 2005. Methyl jasmonate application induces increased densities of glandular trichomes on tomato, Lycopersicon esculentum. J Chem Ecol: 46-46.
- Felton, G. W. 2005. Indigestion is a plant's best defense. Proc Natl Acad Sci 102: 18771-18772.
- Musser, R. O., Cipollini, D. F., Hum-Musser, S. M., Williams, S. A., Brown, J. K. and Felton, G. W. 2005. Evidence that the caterpillar salivary enzyme glucose oxidase provides herbivore offense in solanaceous plants. Arch Insect Biochem Physiol 58: 128-37.
- Musser, R. O., Kwon, H. S., Williams, S. A., White, C. J., Romano, M. A., Holt, S. M., Bradbury, S., Brown, J. K. and Felton, G. W. 2005. Evidence that caterpillar labial saliva suppresses infectivity of potential bacterial pathogens. Arch Insect Biochem Physiol 58: 138-144.
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