Potsdam plant scientists receive Jeff Schell Award for outstanding research achievements

The Max Planck Institute for Molecular Plant Physiology honors excellent young scientists for their research on mobile CRISPR/Cas gene scissors and for revelations on the inheritance of plastids.

June 28, 2023

The Jeff Schell Prize of the Max Planck Institute of Molecular Plant Physiology, endowed with 2500€, is awarded annually in a ceremony at the Max Planck campus in Golm. On June 28, 2023, the institute honored two young scientists, Dr. Lei Yang and Dr. Kin Pan Chung, for their excellent research in recent years.

Dr. Lei Yang developed a mobile genetic scissors to create genetically modified plants that are indistinguishable from plants bred in the traditional way in just one generation.

The development of so-called CRISPR/Cas gene scissors enabled enormous advances in biological research in recent years. In view of advancing climate change and the associated requirement for breeding research to generate varieties that keep pace with changing environmental conditions, this is urgently needed.
With the aid of genetic scissors, it is possible to induce targeted genetic changes in plants. However, this method has the side effect that selection markers and the DNA sequence of the genetic scissors themselves have to be introduced into the plant genome. After the process, the plant thus contains foreign DNA components that have to be crossed out of the plants again over many generations in a laborious and time-consuming process. This prevents the use of this method for breeding plants that have long generation times, such as grapevines or fruit trees.

Migrating scissors
Dr. Yang has been instrumental in developing a new method that can rapidly accelerate the CRISPR/Cas method for such plants by eliminating the need to cross out the foreign DNA from the gene-edited plant. In fact, it is not incorporated in the first place.

Dr. Yang uses two different plants for this purpose. The first plant is genetically modified in the classic way and, as usual, contains the blueprint of a gene scissors in the form of DNA in its cell nuclei. Normally, this blueprint is translated into a short-lived transport form, RNA, which is then used to assemble the functioning gene scissors in the cytoplasm of the plant cell. The finished gene scissors finally modify the DNA at a specific location in the cell nucleus.

Dr. Yang's gene scissors, however, are special. It is designed so that its RNA transport form doesn't just stay in the cell where it is created. Instead, it is transported throughout the plant from the root, all the way into the flowers.

A fusion of modern genetic engineering and traditional grafting
Now Dr. Yang is using an ancient breeding technique that has been used on grapevines and fruit trees for thousands of years – Grafting. It involves combining two plants by grafting the shoot of one plant onto the root of the other. The two parts grow back together, creating a mixed plant with root and shoot from different individuals.
When Dr. Yang grafts the shoot of a second, genetically unmodified plant, onto the roots of the plant with his migrating gene scissors, the RNA blueprint of the gene scissors is transported all the way into the flowers of the unmodified plant. There, the gene scissors are then assembled and modify the DNA of the developing seeds. 

The scissor’s DNA never enters the seeds
Since only the short-lived RNA of the gene scissors migrates, but not the DNA of the gene scissors from the cell nucleus, the DNA of the gene scissors is never incorporated into the seeds of the plant. Thus, the next generation immediately carries the desired gene modification, but no foreign DNA. This makes this plant indistinguishable from conventionally bred plants. 

"Dr. Yang played a major role in developing this process. It is a breakthrough for plant breeding, especially for plants in which breeding successes usually take decades due to long generation times. Since joining my research group as a PhD student in 2013, Mr. Yang has driven our research with great dedication, great ideas, and excellent skills in the lab. I count Lei Yang among the best PhD students and postdocs I ever had the honor to work with," says Dr. Friedrich Kragler, head of the research group for Intercellular Macromolecular Transport, which developed the new method.

About Dr. Lei Yang
Dr. Lei Yang studied in China until 2013, at the Hebei Agriculture University, and at the Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, University of Chinese Academy of Sciences. Since 2013, he has been conducting research on mobile RNA and macromolecule transport in plants at the Max Planck Institute of Molecular Plant Physiology in the research group of Dr. Friedrich Kragler.

Dr. Kin Pan Chung was able to disprove the general assumption that chloroplasts, the solar power plants of plant cells, are solely inherited from the mother.

Plants conduct photosynthesis in chloroplasts to store solar energy. This energy is then consumed in mitochondria to fuel their cells. Chloroplasts and mitochondria originated from bacteria, which have formed a symbiotic relationship with plant cells for more than a billion years and are now inextricably intertwined with the cells of higher plants. Due to their origin, both chloroplasts and mitochondria still contain their own genetic material, which plays a decisive role in determining the properties of a plant.

Unlike the genetic material in the nucleus of plant cells, the chloroplasts and mitochondria genomes are not passed on equally from father and mother to offspring. Instead, they are passed on exclusively by the mother. So we thought.

A way to detect the inheritance of paternal chloroplasts
Despite the common belief that all chloroplasts are inherited from the mother, Dr. Chung and his colleagues were able to show that chloroplasts can indeed be passed on by the father at low temperatures. In the experiments, the research team genetically engineered father plants to make their chloroplasts resistant to an antibiotic. These engineered father plants were grown at low temperatures. Later their pollen was used to pollinate unmodified mother plants that contained normal chloroplasts. Seeds obtained from the cross were then germinated on a nutrient medium supplemented with the appropriate antibiotic, on which only the resistant paternal chloroplasts could survive. Plants with chloroplasts inherited from the father therefore appeared green, while all plants with maternally inherited chloroplasts turned white. 

A higher chance of getting chloroplasts from the father
Since the inheritance of paternal chloroplasts is very rare, Dr. Chung and his colleagues had to check nearly 4 million seedlings to find that the proportion of paternally inherited chloroplasts was about 150 times higher at low temperatures than at normal temperatures. In further experiments, Dr. Chung was then able to identify an enzyme involved in blocking the paternal inheritance of chloroplasts. When father plants with the defective enzyme are grown at low temperatures, 2-3% of the offspring carry paternal chloroplasts, which is around a thousand times more often than usual.

"For breeders, whole new worlds open up if they can use environmental conditions to pass on chloroplasts from the father as well. It now seems possible for the first time to inherit chloroplasts and mitochondria separately. This was previously unattainable as long as both were simply always passed on from the mother. A whole host of other research groups have been trying unsuccessfully for decades to take the first steps toward the molecular mechanisms that control the inheritance of chloroplasts and mitochondria. Dr. Chung is the one who finally made the breakthrough! He is smart, highly motivated and a brilliant scientist, someone who will go wherever the problem leads. A scientist very much in the spirit of Jeff Schell’s research,” Prof. Ralph Bock, head of the Organelle Biology, Biotechnology and Molecular Ecophysiology group who led the project.

“I am glad I had the opportunity to work on this project. The discovery we made is of course exciting, but more importantly, our work is a showcase of extensive scientific collaboration. 
The other two co-first authors Dr. Enrique Gonzalez-Duran and Dr. Stephanie Ruf contributed their expertise, and I’m really happy to see the outcome of our joint effort
,” says the awardee Kin Pan Chung about his work in the project.

About Dr. Kin Pan Chung
Kin Pan Chung studied molecular biotechnology in Hong Kong at the Chinese University of Hong Kong. He obtained his PhD there in 2017, with his doctoral work focusing on autophagy and protein trafficking in plants. Since 2018, Dr. Chung has been conducting research on organelle biology and cytoplasmic inheritance at the Max Planck Institute of Molecular Plant Physiology in the group of Prof. Dr. Ralph Bock.

Jeff Schell, the eponym of the award, revolutionized plant research
The award is named after the Belgian molecular biologist Jozef Stefaan (Jeff) Schell (1935 - 2003). He studied zoology and microbiology at Ghent University, where he worked as a professor from 1967 to 1995. From 1978 to 2000, he was director and head of the department "Molecular Basis of Plant Breeding" at the Max Planck Institute for Plant Breeding Research in Cologne.

Schell was one of the pioneers of biotechnology. As a microbiologist, he was interested in the interactions between plants and soil bacteria. His studies on the formation and development of plant tumors showed that Agrobacterium tumefaciens, which is widespread in the soil, can transfer genes to plants. Subsequently, these research findings led to the possibility of using this bacterium to introduce targeted genes into plants.

The process of transforming plants has since revolutionized plant research, as it can be used to determine the function of genes, enabling plant researchers worldwide to better understand metabolic processes, plant growth and plant development.

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