Polyspermy in plants, as investigated by a group led by Prof Groß-Hardt | Left: Plants can inherit the nuclear genome of three parents due to the rare event of supernumerary sperm fusion to one egg cell. Right: The scientists Dr. Dawit Tekleyohans, Thomas Nakel and Prof. Rita Groß-Hardt (from left to right).
We naturally associate the term "parents" with two individuals, one male and one female. Work at the University of Bremen now shows that this bi-organismic concept must be expanded when it comes to plants: The laboratory of Prof. Rita Groß-Hardt has identified genuine triparental plants, which contain the nuclear genome of one mother and two fathers (Nature Communications, DOI: 10.1038/s41467-017-01044-y).
As part of a European Research Council (ERC) funded project, the team investigates polyspermy, which is the fusion of an egg with more than one sperm. In many organisms including humans polyspermy is lethal. To investigate and monitor this rare event in plants, the Groß-Hardt lab made use of a genetic trick: They disconnected the two gene elements necessary to engineer herbicide resistance and introduced them separately into two different plants. These plants served as fathers and were used to pollinate a third, mother plant. In case of a regular fertilization event involving one sperm from a single father only, an incomplete copy of the gene is inherited, rendering the offspring herbicide sensitive. By contrast, polyspermy, involving sperm from both fathers restores gene function and triparental plants can be identified by herbicide treatment.
"I am extremely grateful for the support we get from the ERC on this project, which allows us to explore this uncharted territory" says Rita Groß-Hardt. "The results of our team, in particular Thomas Nakel and Dr. Dawit Tekleyohans, can have important implications for agriculture, as three-parent crosses provide a novel tool for plant hybridization." In addition, the findings of the scientists shed new light on the evolution of flowering plants: The increase in genomic copies is considered a major driving force for plant evolution and the novel results now suggest that polyspermy has contributed to the amazing flowering plant diversity that shapes our planet.
(© Universität Bremen)