The ancient genetic mechanism used by primitive land plants to produce free-swimming plant sperm has been discovered by researchers.
Investigating the evolution of plant sperm has led to the information about the genetic mechanism which allowed land plants to adapt.
The origins of the ancient genetic mechanism
The team found that the DUO1 gene originated in the stoneworts. The stoneworts are an ancient group of aquatic algae. They diverged from land plants over 700 million years ago.
The new research suggests that a simple change in the DUO1 gene sequence allowed the algal ancestors of land plants to product small swimming sperm which increase the changes of fertilisation in an aquatic environment.
The DNA sequences of DUO1 were compared in primitive land plants, such as liverworts and mosses, to plants in freshwater algae. They were able to show that small genetic changes enabled DUO1 to control a gene network needed to make swimming sperm. They also observed that liverworts with a mutated DUO1 gene were infertile because they were unable to make active sperm.
Professor David Twell said: “It is heartening that a major event in the evolutionary history of plant sperm has been tracked down through international cooperation and the individual efforts of many researchers. Further team effort to assemble the fertility gene networks of our important crop plants, will uncover new ways to help plant breeders in their quest to maintain food security in the face of environmental change.”
The adaptation of the DUO1 gene
The DUO1 gene in plant sperm formation has adapted to the demands of plant life on land.While DUO1 is required to produce the whiplash flagella used for the propulsion of liverwort sperm, this is not the case in the flowering plant Arabidopsis thaliana (thale cress). The sperm of flowering plants do not swim. Instead, they are transported to the egg by a tube which grows out from each pollen grain. In these sperm, DUO1 has taken control of the specialised network of genes needed for the union of sperm and egg.