Plant Chemical Defense based on Mustard Oil Bomb
Kaichiro Endo (postdoc), Toru Maeda (postdoc), Shayan Sarkar (postdoc), Alwine Wilkens (PhD student), Mohamadreza Mirzaei (PhD student), Karolina Małek (technician)
Plants have developed sophisticated defence systems to adapt to environmental changes. The defence system based on glucosinolates, the so-called “mustard oil bomb”, is such a defence system in Brassicaceae. The glucosinolate biosynthesis pathway is evolved from the cyanogenic glucoside synthesis pathway in the plants of order Brassicales. Since Brassicaceae plants have evolutionary gained the glucosinolate biosynthesis pathway but lost a cyanogenic glucoside synthesis pathway, the changing defence chemicals might benefit. Besides, Brassicaceae plants have two different mustard oil bomb systems; one is based on myrosin cells, and another is based on ER bodies. In the project, we will address how Brassicaceae plants came to use these different defence systems and what is the benefit of using the defence system. An overview of the mustard oil bomb based defence system is needed for further understanding the mustard oil bomb defence system, which is essential for the survival of Brassicaceae plants.
According to the preliminary data, mutant seedlings lacking ER bodies are more sensitive to insects that generally would not attack living plants, indicating that the β-glucosidase in ER bodies is responsible for the defence against those insects. This finding is the first example showing that Arabidopsis thaliana has specific resistance mechanisms against certain insects in the seedlings and that these mechanisms are not dependent on myrosinases (TGGs). The finding comes as a surprise, as it was thought for a long time that myrosinases (TGGs) represent the only primary line of defence against insect attacks in Arabidopsis thaliana. Questions arose concerning how the plants of Brassicales order developed two different defence systems in seedlings, roots and leaves. It is proposed that the interaction of plant and herbivores causes the divergence of defence strategies; the specific herbivores develop a tolerance to plant defence chemicals, and this will induce the development of new defence chemicals in plants. However, there is no direct evidence the plant-herbivore interaction directs the divergence of plant defence chemicals, and furthermore, it is still unknown about the impact of the changes of plant defence strategies on the behaviour of insects. The aim of the project is to understand 1) How the plants have established the chemical defence strategies and 2) How the herbivores respond and elude from the plant defence. The results from the proposed project will further explain the sophisticated defence system of plants using a mustard oil system. These findings can be helpful for the agricultural industry by increasing the “toolkit” for the production of pest-resistant plants. In this project, we will collaborate with animal ethologists. Studies on the defence systems of plants and the feeding mechanism of animals have been performed independently. Despite many efforts in each field, there is a lack of research on coevolutionary interaction between plants and herbivorous animals. Our collaboration between plant molecular biologist and animal neuroethologist will provide an innovative breakthrough to figure out the interactive development of their chemical strategies. Namely, the project can generate a new research field in the border of two different research fields.