RUI: EPIGENETIC WEAPONS IN PLANT-HERBIVORE INTERACTIONS: SULFORAPHANE AS A NATURAL HISTONE DEACETYLASE INHIBITOR IN LEPIDOPTERAN PESTS

This project will investigate a novel “epigenetic weapon” that cruciferous plants deploy against destructive insect pests. Epigenetic systems regulate the expression of hundreds of genes by temporarily opening or closing chromosomal segments so that the genes in these segments can be activated or de-activated. These systems direct normal growth and development and allow individuals to respond rapidly to changing environments.

Recently, it has been observed that sulforaphane, a natural substance from cruciferous plants (e.g., broccoli, cauliflower), disrupts the epigenetic control systems of insect larvae while they eat plant leaves. Thus, sulforaphane may serve as an epigenetic weapon against pest insects. This would represent a new category of plant defense, one with the potential to sabotage insect development and thereby protect crop plants.

Preliminary data indicate that the effectiveness of sulforaphane against pest caterpillars depends on the dosage, the temperature, and the pest species. Generalist feeders seem to be most susceptible to this substance. In contrast, specialist insects which co-evolved to feed upon these plants seem to have developed partial resistance, by some unknown mechanism.

To explore this mechanism of resistance, the larval development of three economically important pest species will be examined as they consume various doses of sulforaphane over a range of temperatures. Experiments will determine the impacts of this substance on (1) larval survival and development, (2) the health of adult moths and butterflies, (3) the epigenetic control systems of these insects, and (4) the expression of genes associated with important metabolic pathways and processes.

The possibility that the epigenetic changes induced by sulforaphane may linger, affecting future generations which may not have consumed this substance, will also be evaluated. This project may suggest new methods for protecting crop plants and improve our understanding how plants influence insect populations. It will also support the education of a diverse group of ~20 undergraduates over three years, preparing these students for graduate- and professional-level work in related fields.

Cruciferous plants produce sulforaphane (SFN), an inhibitor of nuclear histone deacetylases (HDACs) which has been investigated as a potential drug and dietary supplement. In humans, sulforaphane consumption alters enzyme activity, DNA-histone binding, and gene expression within minutes. However, the ability of SFN to act as a HDAC inhibitor in nature, disrupting the epigenetic machinery of herbivorous insects, has never been explored.

It is proposed that plants can employ SFN as an “epigenetic weapon”. Preliminary data demonstrate that dietary SFN dramatically reduces the HDAC activity and slows development of the army worm (Spodoptera exigua), sometimes affecting second-generation larvae. In contrast, the cabbage looper (Trichoplusia ni) seems to be partially resistant to SFN.

To explore this further, the investigators will determine how SFN alters development, HDAC activity, histone acetylation, and global gene expression in 1st and 2nd generation larvae of three herbivores which feed on these plants: Pieris rapae (cabbage white), Trichoplusia ni (cabbage looper), Spodoptera exigua (army worm). These responses will be examined over a range of temperatures.

RNA-seq will be used to analyze differential gene expression, orthologous gene groups will be identified, the putative function of differentially expressed genes will be predicted using gene ontology classifications, and differentially expressed genes will be mapped to metabolic pathways. The proposed experiments would, for the first time, test the hypothesis that plant HDAC inhibitors can interfere with the epigenetic machinery of insects. This would represent a new category of plant defense.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.