Drive to survive: The seemingly impossible reproduction of dogroses hinges on a centromere trick

An international research team led by Dr. André Marques from the Max Planck Institute for Plant Breeding Research in Cologne, Prof. Dr. Christiane Ritz from the Senckenberg Museum of Natural History in Görlitz and Dr. Aleš Kovařík from the Institute of Biophysics of the Czech Academy of Sciences has achieved a significant breakthrough in research into the reproduction of dogrose. The study, which has now been published in the renowned journal "Nature", shows how differences in the size of the centromeres - the central docking sites for chromosomes - play a decisive role in the extraordinary chromosome inheritance of these plants. In the long term, the results could open up new avenues for the development of more robust crops.

The dogrose’s secret

The dogrose (Rosa canina) is by far the most common wild rose in Central Europe. Its fruits, known as "rose hips", are used in a variety of ways - from fruit tea blends to the production of "itching powder". "The plant is not only pretty to look at and can be used for all kinds of purposes, but has also developed a special form of reproduction," explains Prof. Dr. Christiane Ritz from the Senckenberg Museum of Natural History in Görlitz and continues: "While most plants and animals each have two sets of chromosomes, the dogrose has five. This makes their reproduction more complicated. An odd number of chromosome sets even often leads to infertility in many plants because the chromosomes cannot be evenly paired and distributed during meiosis - the formation of egg and sperm cells."

However, in the course of their evolution, the dogrose has developed an ingenious solution that still enables the plant to reproduce sexually. In the so-called Canina meiosis or balanced heterogamy, only two of the plant's five chromosome sets mate regularly and are passed on via egg cells and pollen. The other three sets remain unpaired, so-called univalents, and are passed on exclusively via the egg cell - without being changed. "In this way, the plant combines sexual and clonal reproduction," explains Dr. André Marques from the Max Planck Institute for Plant Breeding Research in Cologne and continues: "Although this reproductive system has been known for over 100 years, little was known about the mechanisms of this method. The role of the centromeres - the central chromosome regions that are important for distribution during cell division - was also unclear. In our study, we examined genomes of pentaploid dogroses - plants with five complete chromosome sets - in high resolution down to the level of individual chromosome sets and their origin."

The power of centromeres

The researchers' aim was to find out what enables dogroses to transport their unpaired chromosomes into the egg cell in a targeted manner - a process that was not fully understood until now. The scientists found the answer in the structure of the centromeres, the DNA segments to which the spindle fibers attach during cell division. Spindle fibers are part of a spindle apparatus that moves chromosomes during mitosis and meiosis to ensure an even distribution of chromosomes between the daughter cells.

"Our analysis of the three different pentaploid dog rose species showed that the univalent chromosomes have strikingly large centromeres with multiple repetitions of a rose-specific DNA sequence. These larger centromeres also increasingly bind the protein CENH3, which plays a key role in binding the spindle," says Dr. Aleš Kovařík from the Institute of Biophysics of the Czech Academy of Sciences. This means that the centromere size could be a decisive factor in ensuring that certain chromosomes are retained during asymmetric cell divisions. "By tweaking their centromere size and strength, these plants can literally bias which chromosomes get inherited", adds Marques.

Why it matters

"The simultaneous coexistence of sexual and clonal reproduction in the same genome - controlled by differences in the centromere structure - is a fascinating biological mechanism. However, the discovery not only provides new insights into the fascinating world of plant genetics, but also has practical significance for breeding", says Ritz. Many cultivated plants have more than two sets of chromosomes. This makes their reproduction susceptible to errors, but can also bring advantages such as greater resistance. A better understanding of dog rose reproduction could help to make targeted use of these advantages and stabilize the fertility of polyploid plant species. Marques concludes: "In the long term, our findings could open up new avenues for the development of more robust crops."

END