Algae bear genes for shore leave
The genetic strategy that plants adopted when they conquered the land 500 million years ago can be seen in their genes. Marburg cell biologist Professor Dr. Stefan Rensing and colleagues from all over the world report that genes of Charophyceae algae contain numerous evolutionary innovations that enabled their common ancestor with land plants to colonise and then spread in terrestrial habitats. Today, they published their results in the leading scientific journal Cell where they show that many traits once thought to be land plant-specific were actually present in the genome of their algal ancestor that lived long before life existed on land.
Land plants form an extraordinarily diverse group of living organisms, which exhibit a plethora of adaptations to very different habitats - mighty giant trees are just as much a part of it as tender herbs, mosses as well as flowering plants. "The land plants share a common ancestor with Charophyceae," explains senior author Stefan Rensing from the University of Marburg. The two lines separated more than 500 million years ago. Charophyceae live in fresh water and some of them develop more complex morphology than other related algal species.
When the first plants went ashore, they were confronted with an entirely new set of environmental conditions. For example, the pioneers had to protect themselves from drying out once they left the water. "Several groups of algae colonised the land, but only one group radiated into a diversity of forms that you see growing on the surfaces of continents today – the large group of land plants," explains Rensing. What genetic adjustments occurred when plants left the wet water and moved to the dry land?
An international group of researchers led by the Marburg cell biologist has decoded the genome of Chara braunii, an alga closely related to land plants. By comparing the list of genes that they identified in this aquatic alga with the list of genes found in land plants the team were able to identify the genetic changes that occurred when plants colonized the land. "Our comparative analysis reveals genes that originated in the common ancestors of Charophyceae and land plants," explains the leader of the international programme. Some of these genes have been preserved for hundreds of millions of years. Some new genes evolved after algae and land plants went their separate ways. "These genes represent evolutionary changes associated with the emergence of a diverse morphological complexity as we know it from land plants”.
One of the most striking discoveries that the team of scientists discovered was that these algae use the same genes to control cell division as land plants. "Similar to land plants, Charophyceae carry out cell division in which special proteins assemble a cell plate which develops into a new transverse wall," write the scientists.
"Our data show a number of genes that were previously considered typical for terrestrial plants can already be found in these algae," explains Rensing. “This means that some important processes that occur when land plants grow are much more ancient than previously believed. In fact, some of these characters evolved before land plants even existed.”
However, there are also innovations in Chara braunii that are not present in the land plants and have been lost in related lineages. This means that plants picked some genes to take and left other genes behind when they left the water and colonized the land 500 million years ago.
The University of Marburg cell biologist has made the first steps in understanding one of the key events of life on Earth. Stefan Rensing teaches plant cell biology at the University of Marburg in Germany and is also associated member of the cluster of excellence BIOSS Centre for Biological Signalling Studies at the University of Freiburg. In addition to his research group, scientists from numerous countries participated in the research on which the publication is based. The German Research Foundation, the European Research Council, the Leibniz Association, the US National Science Foundation and research sponsors from Japan, Belgium and Denmark supported the work financially.
Original publication:
The Chara genome: secondary complexity and implications for plant terrestrialization