Anyone who has ever looked after a plant, whether in the field, in the garden or on the window sill, knows how mercilessly pest plants can attack plants. The culprits are quickly identified. Viruses, bacteria, fungi and insects destroy entire crops and benefit from climate change because they spread more in warm summers and suffer less in mild winters. Presently, these pests are mainly fought with pesticides. However, these substances also decimate beneficial insects, reduce biodiversity and pollute the soil and groundwater. Sustainable and environmentally sound solutions are sorely needed.
This is where the European SUSPHIRE project comes in, backed by a consortium from England, Spain, Slovenia and the Federal Republic of Germany. From the German side, three professors of the TU Darmstadt are involved: Heribert Warzecha, Professor of Plant Biotechnology, Andreas Jürgens, Professor of Chemical Plant Ecology, and Alfred Nordmann, Professor of Philosophy. The project has ambitious goals. In the future, moths, mealybugs and the like will no longer be killed by insecticides but prevented from propagating by the unorthodox use of pheromones. Typically, female insects invite males to mate through those sexual attractants, known as pheromones. Warzecha and his colleagues will modify plants by gene transfer in such a way that they also produce pheromones. This will confuse the males in such a way that they will miss the brief window of time for mating and no offspring will be produced. “
Because each species of insect synthesizes its own perfume to prepare for mating, pheromones can be used in a very targeted way to confuse and entice away individual species,” explains Professor Warzecha. “Such a perfume sometimes consists of a single pheromone, sometimes of several pheromones, but it works only for one species and not for others,” continues the pharmaceutical biologist. Pheromones are current ly already used in the form of pheromone traps or sprays. However, the production of these products is very expensive. That's because their chemical structure is complex. Many syntheses are complicated, and much is technically impossible. Therefore, Warzecha and his colleagues want to establish the production of plant pheromones.
Plants as perfect biofactories
Plants have long been used to produce complex proteins or substances because they are a renewable resource and their cultivation can be adapted to respective conditions. That makes them perfect biofactories. With the right construction manuals in the genome, they auto-synthesize even the most complicated molecules, requiring only an advantageous site with enough water, sunlight and carbon dioxide. Today, a whole range of technical enzymes are already produced in plants, as well as cosmetics and a drug for a rare disease.
The fact that plants can also produce insect pheromones was already demonstrated several years ago by the Spanish project partners and other working groups. Professor Diego Orzaez and his colleagues from the University of Valencia introduced the genes for the synthesis of moth pheromones into tobacco. They were able to show that the pheromones thus produced function and attract moths. However, these pheromones are not yet released into the air, but remain in the plant cells. Over time, the group intends to develop solutions. Because the moth males hold the pheromone-producing tobacco plant because of the pheromones for a female, this plant has been given the name “Sexy Plant”. This is a first important prototype. “We know from these results that the concept works in principle,” says Professor Warzecha. “So, we can equip plants to protect themselves from insects, thus giving them relevant agricultural added value.”
Warzecha and his colleagues pursue two fundamental strategies. To begin with, they are concerned with producing insect pheromones or their precursors inexpensively to fill pheromone traps with the isolated substances or use them in sprays. That would significantly reduce the cost of producing such products and make their use significantly more profitable. The long-term goal of the group, however, is to bring the pheromone-producing plants to the field along with the crops. Then, the pheromones would no longer need to be isolated, but could be released by the plants directly into the environment. However, such applications with genetically modified plants are currently subject to strict regulation. “We will not use feed or food plants for the production of the pheromones, but instead, tobacco, and could even bring the plants to the field in special containers,” says Warzecha. “In the coming years, we will work with the authorities to determine what is possible and what is not. The SUSPHIRE project will also address issues of responsible research and the economic consequences of this work”.
Pheromones of mealy bugs
Warzecha and his colleagues are currently also intensively searching for the pheromones of mealy bugs, the citrus mealybug (Planococcus citri). These bugs ruin many harvests by covering citrus plants with a waxy substance. However, before Warzecha and his colleagues can produce the pheromones of citrus mealybugs in plants, they must know the genes so that they can deposit the corresponding building instructions in the plants. “To identify pheromone genes, we will compare all messenger ribonucleic acids produced by fertilized and unfertilized females. In the pool of ribonucleic acids formed by unfertilized females, the blueprint for the pheromones should also be present. We will then transfer the gene with appropriate controls into tobacco plants. Then we must see if enough pheromones are formed and if this happens at the right time and in the right place,” Warzecha continues. He and his colleagues hope to be able to produce a range of pheromones in plants and tailor them for specific applications. The need is great. The world market for insecticides in 2022 should be 17.5 billion euros. The concepts of the consortium are much more environmentally friendly.