A researcher, DNA and rye under stress
When people hear the word “agronomist”, they often think of someone who stands in a field or a barn wearing rubber boots; someone who conducts field trials and only shows up at the office when results have to be put down on paper. Dr Steven Dreissig does not live up to this cliché: “I don’t actually know much about field trials,” admits the agricultural scientist from the University of Halle. His work is done on the computer and yet has the potential to provide valuable insights for agriculture of the future.
The Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) has also seen this potential and has been funding Dreissig’s work since January of this year through an Emmy Noether junior research group. Over a six-year period, the group will receive up to 1.8 million euros to conduct its research.
When he was at school, Steven Dreissig never imagined that his career would one day lead him into research. “I wasn't really interested in science. I almost didn’t pass eleventh grade because of biology,” he recalls. That changed when he got his hands of a copy of the book “Measuring the World” by Daniel Kehlmann. The novel deals with the lives of two of the most famous German scientists: Alexander von Humboldt and Carl Friedrich Gauss. One travelled and explored the world, the other explored it from his desk as a mathematician. The book managed to get Dreissig excited about science. Interested in ecology, he began his bachelor’s degree in agricultural sciences at the University of Halle in 2008. It was there that he developed a serious desire to go into research.
Dreissig also completed his master’s degree in crop science at the University of Halle, during which he took a detour of several months to the University of Dundee. At a lecture, he met his future doctoral supervisor Professor Andreas Houben from the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), who was teaching at the University of Halle at the time. “I approached him after the lecture to see if he had a PhD position for me,” Dreissig recounts, “and was successful!”
At IPK, he was to develop a method to study meiotic recombination in barley pollen. Houben submitted the project proposal - which was subsequently rejected. “The reason they gave was that the proposed method was far too complex and that established methods already existed.” Dreissig’s doctorate received funding from another source. Now he can laugh about the rejection as it is precisely this method that is being used by the Emmy Noether group.
The driving force behind evolution
The junior research group is investigating the interaction between environmental conditions, especially nutrient deficiency, and so-called meiotic recombination. Meiosis (see info box) is the process of cell division in which one cell with a double set of chromosomes becomes four germ cells with a single set of chromosomes. “Recombination occurs in which the arms of two adjacent chromosomes, on which the genetic material is located, overlap and individual gene sequences swap places,” explains Dreissig. This can produce different characteristics in the organism depending on how the gene sequences are exchanged. “I have two daughters. One looks more like my wife, the other more like me,” says the researcher. “Suppose we had 100 children. They would all look relatively similar, but no two would look completely alike, even though they came from the same genetic material.”
This is exactly what happens in all living creatures - especially when they are exposed to adverse conditions. “It is advantageous because the more often genes recombine, the more the offspring generation will differ and the greater the chance it will have of survival,” explains the agricultural scientist. “For example, high temperatures lead to longer chromosome arms. This allows gene strands to better overlap and potentially more recombination takes place.”
According to Dreissig, the methods for finding out what takes place in the genome during meiosis used to be much more time-consuming. “It used to be that plants had to be crossbred, their seeds cultivated and then the genome of the fully grown plant sequenced before any conclusions could be drawn.” His own method is faster. “We know of 80 gene sequences that undergo meiotic recombination.” These produce proteins that the researchers label with fluorescent dyes. This enables them to use a special fluorescence microscope to see which recombination events have taken place and where. “If we only take the pollen and analyse its set of genes, we save having to go through the phases of fertilisation, seed formation and growth.”
As a postdoc at IPK, one of the topics Dreissig has studied is the difference between meiotic recombination in wild and cultivated barley. “Cultivated barley is grown in a relatively protected environment. Wild barley is exposed to a whole range of environmental influences.” In fact, the researchers have found a correlation between the frequency of recombination, its location on the chromosome arms, and external environmental influences.
The advantage of Eternal Rye
In 2019 Dreissig returned to the University of Halle and Professor Klaus Pillen’s plant breeding group. “The work here is going wonderfully. Professor Pillen was extremely supportive of my research right from the start and has given me a lot of freedom.” He has since swapped his position as a research assistant and the possibility of a post-doctoral degree with that of leader of the Emmy Noether group, which also qualifies him for a professorship. At the Institute of Agricultural and Nutritional Sciences, Dreissig will now study how environmental influences change the DNA of rye. Halle is the ideal location for this: the permanent field experiment “Eternal Rye Cultivation” has been conducted here since 1878. This is a test field where, among other things, rye has been grown as a monoculture for more than 140 years. Because the soil in one plot is not fertilised, nutrients here are scarce. This is precisely what interests Dreissig. “Halle provides a unique opportunity to observe, under stable experimental conditions, nutrient deficiency as a stress factor.”
Dreissig harvests the rye pollen from the unripe ears. Working with IPK, the pollen is individually sorted in several steps into mini-reaction vessels. “The genome of each pollen undergoes different forms of meiotic recombination. Therefore, each reaction vessel can contain only one grain of pollen.” After propagating and sequencing the DNA, Dreissig uses bioinformatics to identify where genes recombine. “Normally, this happens one to three times per chromosome.”
Dreissig also wants to observe the selection process over the course of the next few years. “We are saving the harvested seeds and sowing them again next year. That way we can understand which gene sequences will prevail.” The research group’s findings could be incorporated into breeding programmes and improve them. “We can also find out how different gene variants influence evolutionary processes. This is also decisive in determining how resistant a species is to changing environmental conditions,” says the researcher - something which is particularly important in light of the drastic climate change that is currently happening.