Uncovering the Hidden Defences

IGZ Scientist Axel Touw Successfully Defends Doctorate Thesis on Root Herbivory in field mustard

22.10.2024
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: After the Defence – Dr Axel Touw with his supervisor, Prof Dr Nicole van Dam. Photo: M. Barman/IGZ
: After the Defence – Dr Axel Touw with his supervisor, Prof Dr Nicole van Dam. Photo: M. Barman/IGZ

IGZ scientist Axel Touw has successfully completed his PhD at the Friedrich Schiller University Jena, shedding light on the underexplored mechanisms of how plants defend their roots from herbivores. His research, conducted at the interface of ecology, plant pathology, and entomology, delves into the chemical and ecological responses of Brassica rapa to root herbivory, offering insights with implications for both ecology and horticulture.

Axel Touw’s PhD journey began at the German Centre for Integrative Biodiversity Research (iDiv) in Jena, where he focused on plant-insect interactions under the supervision of Prof. Nicole van Dam. When Prof. van Dam assumed the position of Scientific Director at the Leibniz Institute of Vegetable and Ornamental Crops (IGZ), Touw continued his research in Großbeeren, further deepening his exploration into the defence mechanisms of plants below ground. Recently, Touw successfully defended his PhD thesis titled “Down to the Roots: Studying the Mechanisms and Ecological Consequences of Belowground Defence Responses in Brassica rapa.” His work investigates how plants respond to herbivory by the cabbage rootfly (Delia radicum L.), focusing on the largely overlooked area of root defence.

Plants are known for their complex chemical defences that help resist attacks from insect herbivores, pathogenic microorganisms, and parasitic nematodes. While many defence traits are always present, others are inducible, emerging in response to specific threats. As plant pathologist and entomologist, Axel Touw focused on these inducible defences, specifically how Brassica rapa adjusts its production of specialized metabolites when faced with root herbivory. He found that root herbivory by D. radicum larvae led to an increase in indole glucosinolates (indole GSLs) at the site of the attack, suggesting that these compounds are crucial for the plant’s response to mechanical damage and microbial infection.

Interestingly, the study also uncovered a complex trade-off: while the increase in indole GSLs might bolster the plant’s defence against pathogens, it also comes at the cost of reducing aliphatic GSLs. This shift makes the plant more susceptible to other attackers, including the root-knot nematode (Meloidogyne incognita), a common pest in agricultural systems. This finding has broader implications for crop breeding, as it highlights the delicate balance plants must strike between different forms of defence.

Touw's work provides new insights into the indirect roles that antimicrobial compounds—produced after GSL hydrolysis—play in modulating the plant’s interactions with soil microbes. He demonstrated that these compounds not only affect the plant’s defence against herbivores but also disrupt beneficial microbial communities associated with the insect attackers, thus altering the dynamics of plant-insect interactions.

Axel Touw’s research fills a significant gap in our understanding of belowground plant defences. His findings could influence future horticultural practices, particularly in breeding crop varieties that are better equipped to manage multiple soil-borne threats. As he explains, “The interactions between organisms in the root system are complex and multifaceted. Understanding these dynamics is crucial not just from an ecological standpoint but also for practical applications in agriculture.”

Axel Touw is now continuing his research at IGZ as a postdoctoral scientist in the Research Group “Plant Biotic Interactions” headed by Dr Franziska Beran. In addition to his research responsibilities, he also serves as PostDoc representative at IGZ, a role he has held since March 2024, actively contributing to the institute’s scientific community.

We congratulate Dr Axel Touw on completing his doctorate and look forward to his continued professional success at IGZ.

Relevant publications:

  • Touw, A. J., van Dam N. M. (2023) Optimal chemical defence allocation in roots: where, why and how? Phytochem Rev. doi: 10.1007/s11101-023-09872-1
  • Touw, A. J. et al. (2020) Both Biosynthesis and Transport Are Involved in Glucosinolate Accumulation During Root-Herbivory in Brassica rapa. Front. Plant Sci. doi: 10.3389/fpls.2019.01653
  • Touw, A. J.; van Dam, N. M. (2022) How Do Plants Defend Themselves From Root-Eating Creatures?. Front. Young Minds. doi: 10.3389/frym.2022.660701