Project 11

Tiny beetle with a chemical weapon: Do flea beetles use mustard oils against predators and pathogens?

Supervisors: Franziska Beran, Jonathan Gershenzon, MPI for Chemical Ecology

Background: Plants and animals are well-known to use chemical weapons to defend themselves against enemies. When this chemical defence is produced by the organism itself, a major challenge is to store the toxin safely, but ready for action when needed. Plants have solved this problem by developing two-component defence systems (Morant et al. 2008). The best studied example is the so-called 'mustard-oil bomb' in crucifers, where high amounts of non-toxic mustard-oil glucosides (glucosinolates) are stored in all plant tissues but separately from a specific β-thioglucosidase enzyme known as myrosinase (Halkier & Gershenzon 2006). When the plant tissue is damaged by herbivore feeding, mustard oil glucosides are rapidly degraded by myrosinase to toxic mustard oils (isothiocyanates). These are responsible for the sharp taste of mustard and wasabi. Due to their high reactivity, mustard oils have broad activity against bacteria, fungi, nematodes, and small herbivores. We had previously shown that Phyllotreta flea beetles emit toxic mustard-oils that are derived from sequestered mustard oil glucosides, which are activated by the beetle’s own myrosinase (Beran et al. 2011; Beran et al. 2014). However, we recently discovered that Phyllotreta actually possess several myrosinases that are differentially expressed in different life stages. These results strongly suggest one or more defensive roles of the mustard oil bomb for this insect, but the costs, benefits and targets of this strategy are unknown.

Project description: The goal of the project is to elucidate the roles of sequestered mustard-oil glucosides and mustard oils in Phyllotreta larvae and beetles in defense against entomopathogenic bacteria, fungi, and nematodes, as well as arthropod predators. Therefore, you will analyze how the insect mustard-oil bomb is organized and controlled to prevent self-intoxication in larvae and adults. To assess the ecological function, you will manipulate the levels of myrosinase activity in Phyllotreta larvae and beetles by RNA interference and CRISPR-Cas9, and compare the performance and fitness of insects with functional and suppressed chemical defense.  You will perform assays with different guilds of beetle ‘enemies’ to assay the effectiveness of their defensive phenotype in deterring predatory attack.

Candidate profile: We are searching for a highly motivated student with a scientific and curiosity-driven attitude and a strong interest in interdisciplinary research combining molecular biology, chemistry, and ecology. Excellent communication skills and proficiency in written and spoken English is required.

References:

  • Beran F, Mewis I, Srinivasan R, et al. (2011) Male Phyllotreta striolata (F.) produce an aggregation pheromone: identification of male-specific compounds and interaction with host plant volatiles. Journal of Chemical Ecology
  • Beran F, Pauchet Y, Kunert G, et al. (2014) Phyllotreta striolata flea beetles use host plant defense compounds to create their own glucosinolate-myrosinase system. Proceedings of the National Academy of Sciences of the United States of America
  • Halkier BA, Gershenzon J (2006) Biology and biochemistry of glucosinolates. Annual Review of Plant Biology 57, 303-333.
  • Morant AV, Jorgensen K, Jorgensen C, et al. (2008) beta-glucosidases as detonators of plant chemical defense. Phytochemistry 69, 1795-1813.

 

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