Research team from the Kiel Plant Center investigated how plant cell wall components support adaptation to land-based life
The transition from aquatic to terrestrial life was one of the greatest challenges during the evolution of plants. About 500 million years ago, some evolutionary ancestor of today's land plants succeeded in making this drastic change in habitat, thus creating the basis of today's plant diversity. Researchers from the Department of Pharmaceutical Biology at the Pharmaceutical Institute of Kiel University led by Professor Birgit Classen are studying the adaptation of the plant cell wall to these changed conditions. As an interface between plants and the environment, the cell wall is of major importance. A deeper understanding of the transition to terrestrial life and the new stress factors associated with it also allows conclusions about how plants can adapt to global change. As part of a new research project, the scientists, who are also active in the Kiel Plant Center (KPC), were able to gain new insights into the evolution of individual cell wall components and thus learn more about the relationships and origins of algae and land plants. Together with a multidisciplinary team from Hamburg and Innsbruck, the Kiel researchers recently published their new results in The Plant Journal.
Freshwater algae provide information about adaptation processes millions of years ago
The Kiel research team with Dr Lukas Pfeifer and Professor Classen is investigating this particular research question also in the framework of the priority programme of the German Research Foundation (DFG) "MAdLand: Molecular Adaptation to the Land: Evolutionary Adaptation of Plants to Change". The collaborative research project aims to shed more light on this transition and the necessary changes at the molecular level.
In the new study, the researchers focused on characterising the cell walls of Nitellopsis obtusa (Charophyceae) and Spirogyra pratensis (Zygnematophyceae). Both groups of freshwater algae show a close evolutionary relationship with land plants, although it has recently been shown that the evolutionary ancestor of land plants was closer to the Zygnematophyceae. In particular, the so-called arabinogalactan-proteins (AGPs) were of great interest to the Kiel researchers, as they are present in all land plants and play an important role in various processes of the seed plant life cycle.
The analytical investigations showed that similar structures are present in the more closely related algae species Spirogyra pratensis, while they are not present in the somewhat more distantly related species Nitellopsis obtusa. "Interestingly, at first glance, the carbohydrate structures from Spirogyra hardly differed in their basic structure from those of land plants. However, closer examination revealed that the essential name-giving monosaccharide arabinose was almost completely absent in Spirogyra and replaced by another sugar monomer called rhamnose," says Pfeifer, first author of the study. Therefore, the researchers propose the name rhamnogalactan-proteins (RGP) for this unusual group of molecules. The scientists from Innsbruck involved in the work supplemented the laboratory work on the cultivated Spirogyra sample from the Hamburg algae collection with wild-collected Spirogyra samples from Tyrol.
Possible involvement of the molecules in the sexual reproduction of the algae
With the help of a specific staining of the AGPs, the research team was able to show that the detected molecules were found in larger quantities in the corresponding cells during sexual reproduction of the algae. "What is primarily done in land plants by pollinating insects or by the wind, is done in this group of algae by the individual algae themselves by forming solid bonds between two algae - so-called conjugation bridges", explains Pfeifer.
"Our results are also very interesting because AGPs are considered important signalling molecules in land plants in the process of sexual reproduction. Apparently, the precursor molecules of AGPs, i.e. the newly discovered rhamnogalactan-proteins, were already important for sexual reproduction in these Spirogyra algae. Our new results lead us another step closer to a better understanding of the evolution and function of these molecules," Classen summarises. The research team hopes to be able to successfully continue the investigation of these cell wall components, which are apparently essential for life on land, in a future continuation of the DFG priority programme.
Prof. Birgit Classen
Kiel Plant Glycan Group, Pharmaceutical Biology,
Pharmaceutical Institute, Kiel University:
+49 (0) 431 880-1130
The interdisciplinary centre for applied life sciences – Kiel Life Science (KLS) – links research at the CAU from the fields of agricultural and nutritional sciences, the natural sciences and medicine. It forms one of four research focus areas at Kiel University, and is aimed at achieving a better understanding of the cellular and molecular processes with which organisms respond to environmental influences. The research is focussed on issues such as how agricultural crop plants adapt to specific growth conditions, or how illnesses can arise through the interaction of genes, individual lifestyle and environmental factors. Health is always viewed holistically in the context of evolution. Under the research focus’ name, there are currently around 80 scientists from 40 institutes and six faculties from Kiel University working collaboratively as full members.