Ancestors of land plants revealed

Scientists identify freshwater green algae as the base form of all land plants


All land plants share a common ancestor in the freshwater green algae of the lineage zygnematales (conjugales). This is the result of research undertaken by scientists of the Botanical Institute of the University of Cologne, the Fritz Lipmann Institute in Jena and Université de Montrèal in Montréal, Canada. The findings of the study refute the current hypothesis on land plants. Up until now it was assumed that charales were the closest sister group of land plants as they are the most morphologically complex freshwater algae and share structural similarities with land plants. The result of the research is an important step in the understanding of the evolution of land plants. The study was published in the journal BMC Evolutionary Biology. The Cologne botanist Dr. Burkhard Becker is in charge of the project.

The objective of the project was to clarify the phylogenetic relationships within orders of algae that educed land plants. In doing so, the so-called sister group of land plants needed to be identified – the algae groups, with whom land plants are most closely related. In order to do this, the biologists examined the DNA of forty types of green algae and land plants. The scientists identified a sequence of 129 proteins. By comparing the proteins of land plants and green algae they were able to draw conclusions about the evolutionary history and phylogeny of the examined algae. “And then the surprising finding was revealed, that is, that conjugales (zygnematales), rather than charales, are the sister group of land plants,” says Burkhard Becker.

This new finding is important for evolutionary biology: “If one wishes to understand the biology of land plants today, it has to be done within the context of their evolution,” explains the botanist. “The developmental history is important for [study of] features of today’s land plants.” This is because if one wishes to understand the developmental history properly, then one has to know which algae groups are the mostly closely related because these algae groups possess many features that decisively influenced many further developments on land. The study is also interesting because it corrects the widely assumed misunderstanding that evolution always results in more complicated organisms.
In the case of zygnematales algae it becomes clear that this does not always hold true. “Today’s zygnematophyceae have a decidedly more simple make-up than charales,” says Burkhard Becker. “In evolutionary science it is increasingly seen that there is also 'reductive evolution' where evolution simplifies complexity.” Zygnematophyceae are a favourite object, even for amateurs, of microscopy due to their beautiful form.

In the future the researchers plan to continue their research of this group of algae in order to answer the fascinating question: what makes this algae so different that land plants could develop from it? As land plants are monophyletic, which means that they descended from a common evolutionary ancestor, the features of zygnematophyceae are of special significance, says Becker: “Can one explain why land plants were educed from this algae group in particular and not another?”

Fuente: University of Cologne, Universität zu Köln