Abstract
Diabrotica virgifera virgifera larvae are root-feeding insects and significant pests to maize in North America and Europe. Little is known regarding how plants respond to insect attack of roots, thus complicating the selection for plant defense targets. Diabrotica virgifera virgifera is the most successful species in its genus and is the only Diabrotica beetle harboring an almost species-wide Wolbachia infection. Diabrotica virgifera virgifera are infected with Wolbachia and the typical gut flora found in soil-living, phytophagous insects. Diabrotica virgifera virgifera larvae cannot be reared aseptically and thus, it is not possible to observe the response of maize to effects of insect gut flora or other transient microbes. Because Wolbachia are heritable, it is possible to investigate whether Wolbachia infection affects the regulation of maize defenses. To answer if the success of Diabrotica virgifera virgifera is the result of microbial infection, Diabrotica virgifera virgifera were treated with antibiotics to eliminate Wolbachia and a microarray experiment was performed. Direct comparisons made between the response of maize root tissue to the feeding of antibiotic treated and untreated Diabrotica virgifera virgifera show down-regulation of plant defenses in the untreated insects compared to the antibiotic treated and control treatments. Results were confirmed via QRT-PCR. Biological and behavioral assays indicate that microbes have integrated into Diabrotica virgifera virgifera physiology without inducing negative effects and that antibiotic treatment did not affect the behavior or biology of the insect. The expression data and suggest that the pressure of microbes, which are most likely Wolbachia, mediate the down-regulation of many maize defenses via their insect hosts. This is the first report of a potential link between a microbial symbiont of an insect and a silencing effect in the insect host plant. This is also the first expression profile for a plant attacked by a root-feeding insect.
Highlights
Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) or the western corn rootworm (WCR), are significant pests to maize in North America and Europe
Untreated WCR induced a down-regulation of maize defense genes in relation to the antibiotic treated WCR and the control treatments
The antibiotic treated WCR induced an up regulation of maize defenses in relation to the untreated WCR and the control treatments
Summary
Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) or the western corn rootworm (WCR), are significant pests to maize in North America and Europe. Plants recognize and respond to insect attack through a variety of physiological, biochemical and molecular responses which include the release of volatiles and the production of proteins or metabolites that hinder the biology of the offending insect. These defenses can be classified into three categories which include bolstering of cell wall defenses, production of phytoalexins and the production of pathogenesisrelated (PR) proteins. Phytoalexins include almost every toxic chemical produced following insect or microbial attack These chemicals include volatiles as well as salicylic acid and jasmonic acid related products. PR-proteins are non-detectable in healthy tissue and exhibit increased levels following microbial or insect attack [6]
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