Within the department of Plant Physiology we study and teach about plant signalling in response to various environmental factors. I focus on defence against pests via the production of secondary compounds in tomato glandular tissues. The general aim of my research is to explore natural variation in wild tomato trichomes, to identify metabolites, genes and regulatory elements needed to reconstruct natural and sustainable defence pathways in cultivated tomato.
A crop and it’s problems
Cultivated tomatoes, one of the world’s most important vegetable crops, are hampered in the ability to effectively defend themselves against agricultural pests. Tiny insects such as whiteflies cause large economic losses especially in production areas where tomatoes are grown outside, or semi-closed greenhouses. Conventional control of whiteflies is difficult. Outbreaks of specifically Bemisia tabaci are associated with the emergence of Gemini viruses which they vector.
Loss of traits in the cultivation process
Centuries of breeding selected on traits such as yield and fruit characteristics. Culturing in protected greenhouses and the (heavy) use of insecticides has led to a loss of natural insect resistance still accomplished in wild tomato ancestors via the production of secondary compounds. Wild tomatoes produce a wide variety of defence-related metabolites including flavonoids, acylsugars, alkaloids, ketones and a huge variety of terpenes and terpene-related compounds. These are mainly produced in specialised glandular hairs called trichomes. Trichomes are like biochemical factories, present on the surface of green tissues. Where wild tomato fruits are covered in trichomes, they are absent on ripe fruits of the cultivated tomato because the hairy fruit trait has been selected against.
Rearming the cultivated tomato plant
Previously we have shown that association between metabolome data and insect repellence can be a successful approach for the identification of defence compounds in wild tomato accessions. We identified specific terpenes with repellent properties to whitefly. To identify the terpene synthases responsible trichome-transcriptomes of several wild and cultivated tomatoes were created using an RNA-seq approach. This resulted in the identification of several trichome-specific sesquiterpene-synthases and by targeted mining of the public genome databases the collection was extended to 44 terpene synthases. Finally, this led to the discovery of 7-epizingiberene synthase, a novel type sesquiterpene synthase in wild tomato, that once introduced in the trichomes of cultivated tomato, led to enhanced resistance to pest organisms of different classes
The biosynthesis of defence compounds is costly and therefore under tight regulation. Whereas the biosynthetic genes for the production of terpenes are largely identified, not much is known about the regulation of these terpene biosynthetic pathways. To date only a few transcription factors involved in the regulation of metabolite production in plants are known. So, in order to re-introduce natural resistance knowledge on the biosynthetic pathways and how these are regulated in tomato trichomes is required. Using an ‘-omics approach’ in combination with natural variation in metabolite production and insect resistance, we aim to unravel causal metabolites and the genes that govern them. By linking defence-allele frequency to the resistance phenotype we will be able to apply our findings in the agricultural industry. Implementation of our findings will contribute to sustainable tomato production.
Application of findings in crops
One of my goals is to apply academic research findings to agricultural industry. My affiliation to the University of Amsterdam is uniquely combined with a position at the vegetable breeding company Enza Zaden in Enkhuizen, which allows for combining the best of both worlds. Enza Zaden is a technologically advanced and independent vegetable seed company that greatly values entrepreneurship, expertise and creativity.
I work in the Plant Physiology department headed by Prof. Dr. Michel Haring. Other staff members are:
Dr. Robert Schuurink (Plant volatile signaling),
Dr. Teun Munnik (phospholipid signaling in plant stress and development) and
Dr. Christa Testerink (osmotic stress induced signals that shape the plant root).