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Stefan Rensing investigates the evolutionary transition from algae to land plants

How did plants manage to move out of the ocean and start living on the land? How did flowering plants become so diverse? Comparative genomics is able to clarify the relationships between different species and between species groups and thus contribute to finding answers to the big questions of evolutionary biology. However, such questions can only be answered using bioinformatics. The biologist Prof. Dr. Stefan Rensing from the University of Freiburg has been involved in introducing the use of computers to the life sciences from the very beginning. His analyses of the moss genomes now help to close an important gap in evolutionary research: how did algae become land plants?

Prof. Dr. Stefan Rensing © private

Mosses are quasi-composite beings as they combine the characteristics of algae and higher plants. Moss morphology is not very complex, and mosses are closely related to water-dwelling green algae. In addition, they are physiologically well adapted to a broad range of different types of stress that only occur on land, for example dehydration. Mosses therefore represent a transition stage of evolution. “Algae evolved into flowering plants over a time period of around one billion years,” said Dr. Stefan Rensing, who is associate professor in the Faculty of Biology at the University of Freiburg.

“Mosses were the halfway point in the evolution of algae to land plants; moss-like green organisms were the first to colonise the land.” Amongst other things, Rensing is currently investigating the evolutionary processes that are thought to have taken place sometime between the development of pristine and more modern green plants. In order to find out exactly when this transition took place, researchers need to focus on a broad range of plants in order to find the phylogenetic links between them. This type of investigation involves the use of bioinformatics tools that enable scientists to compare DNA sequences, gene families or proteins. Such comparisons are a prerequisite for the clarification of phylogenetic relationships.

Recognised as an important model organism

The moss Physcomitrella patens has become an important model organism for laboratory investigations © Stefan Rensing

Stefan Rensing, who was born in Freiburg in 1967, was a major driver in the integration of the computer sciences into the field of biology. He studied biology in Freiburg from 1986 to 1993. During his doctoral thesis, which he completed in 1995, Rensing used newly emerging bioinformatics methods. He compared the sequence data of gene families of different algal species with each other in order to uncover the phylogenetic relationships between them. In 2004, Rensing and seven colleagues (including, amongst others, Prof. Dr. Ralf Reski from Freiburg) founded the International Moss Genome Consortium. He was also one of the researchers to decipher the first genome of a moss plant between 2005 and 2008. The moss Physcomitrella patens has since become an important model organism in laboratories around the world. Before the moss became a popular model organism, researchers tended to use either the gene sequences of flowering plants such as Arabidopsis thaliana, plants of economic interest such as rice or they concentrated on the genome of unicellular green algae, which enabled them to study molecular life processes in the laboratory. These investigations have since led to the clarification of important gaps in the evolution of algae to higher plants.

Selaginella moellendorffii - member of the clubmoss family. © Purdue Genomics

In 2007, Rensing habilitated in the field of comparative genomics. Rensing and his team of eight have participated in numerous genome sequence analyses. One of their latest achievements is the publication of the sequence of a member of the clubmoss family (Selaginella moellendorffii) in the renowned scientific journal Science, a study carried out in cooperation with around forty partners from around the world. The Freiburg researchers’ contribution to this project was an analysis that enabled contaminations in the DNA under investigation to be excluded. In addition, they also designed rules and standards that enable the detection of proteins that are involved in the transcription of genes, including a specifically designed computer programme that searches genomes for domains that code for transcription factors or proteins that control transcription. Rensing and his team then provide these data to the international research community. “A project that involves the analysis of genomes requires the cooperation of numerous scientists,” said Rensing highlighting the need to work together in larger research groups.

Complex signalling during evolutionary development

Rensing and his team not only focus on mosses; they also work with other plants including simple algae and higher flowering plants. The researchers are investigating the evolutionary relationships between these plant species, which requires them to take into consideration the full range of plants. Which genes were needed to enable plants to live on land? The comparison of the gene sequences of algae, mosses and flowering plants led to the discovery of stress tolerance genes that protect plants from dehydration and that are not found in algae. As a member of the Freiburg Initiative for Systems Biology (FRISYS), Rensing is also interested in the regulation of genes. An example of this work is a project being carried out in collaboration with Dr. Hauke Busch from the Center of Biological Systems Analysis (ZBSA) in Freiburg, which focuses on the complex signalling processes during the development of plant stem cells. The investigation of dynamic cellular processes on the molecular level also relies on the use of bioinformatics tools.

In 1997, Rensing and one of his university friends founded a company called dnaX. The biologists isolated, stained and embedded human DNA into transparent epoxide, so that people could have their DNA encased in a pendant on a necklace. The response to this offer was enormous. The company’s service was actually so popular that Rensing and his partner could have gone on to invest and expand. However, Rensing chose to become a full-time scientist rather than a full-time businessman. And his research activities are seemingly endless. In the not-too-distant future, the genome sequences of other organisms will be published, and Rensing and his team have once again contributed to the deciphering of these genomes. “Comparative genomics means the sequencing of as many genomes as possible and covering as many evolutionary points in time as possible,” said the biologist. It is worth noting that this type of research is not only of interest to a basic researcher attempting to answer the big questions of evolution. The example of stress tolerance genes highlights the importance of mosses and other plants in economic terms, as the understanding of how abiotic stress is regulated can help make crops more resistant to stress, hence increasing the yield.

Further information:

Apl. Prof. Dr. Stefan A. Rensing
Bioinformatics and Systems Biology
FRISYS, Faculty of Biology
University of Freiburg
Hauptstr. 1
D-79104 Freiburg
Tel.: +49 761/ 203 - 6974
E-mail: stefan.rensing(at)biologie.uni-freiburg.de

Website address: https://www.gesundheitsindustrie-bw.de/en/article/news/stefan-rensing-investigates-the-evolutionary-transition-from-algae-to-land-plants