Progress 08/01/03 to 07/31/06
Outputs
We have shown that naturally occurring plant calcium oxalate crystals play a very important and effective role in plant defense against chewing insects. Mutant lines of Medicago truncatula that lack calcium oxalate crystals were compared, in terms of responses to insects, with normal M. truncatula plants that accumulate calcium oxalate crystals. Caterpillar larvae of the beet armyworm, Spodoptera exigua, show a clear feeding preference for tissue from calcium oxalate defective mutant lines cod5 and cod6 in choice-test comparisons with wildtype M. truncatula. Compared to their performance on mutant lines, larvae feeding on wildtype plants with abundant calcium oxalate crystals suffer significantly reduced growth and increased mortality. Induction of wound-responsive genes appears to be normal in cod5 and cod6, indicating that these lines are not deficient in induced insect defenses. Electron micrographs of insect mouthparts indicate that the prismatic crystals in M.
truncatula leaves act as physical abrasives during feeding. Food utilization measurements show that after consumption, calcium oxalate also interferes with the conversion of plant material into insect biomass during digestion. In contrast to their detrimental effects on a chewing insect, calcium oxalate crystals do not negatively affect the performance of the pea aphid, Acyrthosiphon pisum, a sap-feeding insect with piercing-sucking mouthparts. All of the data thus far show that plant calcium oxalate crystals have a dramatic negative effect on insect growth and performance. Addition of small, amorphous commercial preparations of calcium oxalate to artificial diet did not have a negative effect on insect growth. Coupled with our findings using leaves as insect food, this indicates that the size and shape of calcium oxalate crystals is very important in determining the overall effects on insect performance. The findings suggest that this trait could be a very important and common means
of natural insect resistance in plants. The results confirm a long-held hypothesis for the defensive function of these crystals, and point to the potential value of genes controlling crystal formation and localization in crop plants.
Impacts
We have shown that naturally formed mineral crystals in plants can serve as a very effective insect defense. We have used careful feeding studies with chewing insects to confirm a long-held hypothesis regarding a defensive function for calcium oxalate crystals in plants. Because calcium oxalate crystals are commonly formed by many plant species, it is likely that they are a widely used, and underappreciated form of natural defense. If we can understand how these crystals are formed in plants, then altering those mechanisms might lead to more effective, and environmentally friendly means of controlling chewing insect pests in crop plants.
Publications
- Korth, K.L., Doege, S.J., Park, S.-H., Goggin, F.L., Wang, Q., Gomez, S. K., Liu G., Jia L., and Nakata, P.A. (2006) Medicago truncatula mutants demonstrate the role of plant calcium oxalate crystals as an effective defense against chewing insects. Plant Physiol. 141: 188-195.
- Bede, J.C. Musser, R.O. Felton, G.W., and Korth, K.L. (2006) Caterpillar herbivory and salivary enzymes decrease transcript levels of Medicago truncatula genes encoding early enzymes in terpenoid biosynthesis. Plant Mol. Biol. 60:519-531.
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Progress 01/01/05 to 12/31/05
Outputs
The project has examined the role of a common insoluble mineral in plant interactions with insect pests. Mutant lines of Medicago truncatula that lack calcium oxalate crystals are being compared, in terms of responses to insects, with normal M. truncatula plants. As a first step in addressing the potential role of calcium oxalate in plant defense, we tested the cod5 and cod6 mutants of M. truncatula for gene induction in response to wounding and to a signal mediator involved in wound responses. Methyl jasmonate is a well-characterized plant compound known to trigger, and to be involved in, many signaling processes of plant wound responses. Wound- and methyl jasmonate-induced gene expression are normal in the cod5 mutant. Therefore, it appears that plant responses to insects are normal in the cod mutants. Beet armyworm caterpillars prefer to feed on cod5/6 tissue compared to wildtype M. truncatula leaves in choice tests. In addition, insects grow larger and faster on
cod mutant tissue. Finally, food utilization studies indicate that cod tissue is converted to insect body mass more readily than wildtype tisse containing calcium oxalate. All of the data thus far show that calcium oxalate crystals have a dramatic negative effect on insect growth and performance. The findings suggest that this trait could be a very important, and common means of natural insect resistance in plants.
Impacts
We have shown that naturally formed mineral crystals in plants can serve as a very effective insect defense. We have used careful feeding studies with chewing insects to confirm a long-held hypothesis regarding a defensive function for calcium oxalate crystals in plants. Because calcium oxalate crystals are commonly formed by many plant species, it is likely that they are a widely used, and underappreciated form of natural defense. If we can understand how these crystals are formed in plants, then altering those mechanisms might lead to more effective, and environmentally friendly means of controlling chewing insect pests in crop plants.
Publications
- Korth, K.L., Doege, S.J., Park, S.-H., Goggin, F.L., Wang, Q., Gomez, S. K., Liu G., Jia L., and Nakata, P.A. (2006). Medicago truncatula mutants demonstrate the role of plant calcium oxalate crystals as an effective defense against chewing insects. Plant Physiol. (in press).
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Progress 01/01/04 to 12/30/04
Outputs
This project seeks to examine the role of an insoluble, naturally formed plant mineral in interactions with insect pests. Mutant lines of Medicago truncatula that lack calcium oxalate crystals are being compared, in terms of responses to insects, with normal M. truncatula plants. As a first step in addressing the potential role of calcium oxalate in plant defense, we tested the cod5 mutant of M. truncatula for gene induction in response to wounding and to methyl jasmonate, a signal mediator involved in wound responses. Methyl jasmonate is a well-characterized plant compound known to trigger, and to be involved in, many signaling processes of plant wound responses. Wound- and methyl jasmonate-induced gene expression appear normal in the cod5 and cod6 mutants, as tested by induction of a few well-characterized wound-induced genes. We have expanded this study to include analysis of gene expression as determined via microarray analysis. We are utilizing M. truncatula
microarrays containing approximately 16,000 oligonucleotide gene fragments to compare cod5 gene expression with that of the wildtype parental line. We have determined that chewing insects prefer to feed on mutant lines that lack crystals, and that they grow larger and faster when they feed on mutants lacking calcium oxalate, than they do on normal wildtype plants. Mortality studies have indicated that insect larvae do not survive as well on plant lines with normal amounts of calcium oxalate crystals. Addition of high amounts of commercial preparation of calcium oxalate to artificial diet is deleterious to insect growth and survival, although the levels needed to impair insect growth are much higher than the levels found in wildtype M. truncatula. The differences in results might be due to the differences in size and shape between commercial preparations of calcium oxalate and those found in wildtype M. truncatula.
Impacts
We have initiated a project to answer fundamental questions about what is perhaps a common means of natural insect control by many plants. With the plant lines we will use, we should be able to address a long-held hypothesis regarding a function of calcium oxalate crystals in plants. Understanding whether these crystals function in insect defense could ultimately lead to new tools for insect control in plants.
Publications
- No publications reported this period
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Progress 07/01/03 to 12/31/03
Outputs
This project seeks to examine the role of a common insoluble mineral in plant interactions with insect pests. Mutant lines of Medicago truncatula that lack calcium oxalate crystals are being compared, in terms of responses to insects, with normal M. truncatula plants. As a first step in addressing the potential role of calcium oxalate in plant defense, we tested the cod5 mutant of M. truncatula for gene induction in response to wounding and to a signal mediator involved in wound responses. Methyl jasmonate is a well-characterized plant compound known to trigger, and to be involved in, many signaling processes of plant wound responses. Wound- and methyl jasmonate-induced gene expression are normal in the cod5 mutant. Furthermore, it appears that chewing insects prefer to feed on mutant lines that lack crystals. Finally, chewing insects grow larger and faster when they feed on mutants lacking calcium oxalate, than they do on normal wildtype plants.
Impacts
We have initiated a project to answer fundamental questions about what is perhaps a common means of natural insect control by many plants. With the plant lines we will use, we should be able to address a long-held hypothesis regarding a function of calcium oxalate crystals in plants. Understanding whether these crystals function in insect defense could ultimately lead to new tools for insect control in plants.
Publications
- No publications reported this period
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