It was previously thought that land plants evolved from stonewort-like algae. However, new research published in BioMed Central's open access journal BMC Evolutionary Biology shows that the closest relatives to land plants are actually conjugating green algae such as Spirogyra. Ancestors of green plants began to colonise the land about 500 million years ago and it is generally accepted that they evolved from streptophyte algae (a group of green, fresh water algae). But this group of algae is very diverse and currently ranges from simple, one cell, flagellates to more complex, branching, algae such as stoneworts (Chara). It was thought that Charales were the closest relatives to land plants because they share (amongst other characteristics) a similar method of fertilisation, oogamy, with a large egg and small swimming sperm. For flowering plants this sperm is contained within pollen grains. In contrast, another type of streptophytes, the Zygnematales, use conjugation, a method of reproduction where the gametes are of equal size, isogamy, and one or both crawl, amoeba-like, into a fertilization tube where they meet and fuse. Some phylogenetic analysis had been done previously, on a smaller number of genes, which seemed to support the Charales theory. However, a multinational team, involving researchers in Germany and Canada, analysed genetic divergence in 129 genes from 40 different green plant taxa. This data showed that, despite the differences in reproductive strategy, the closest living relatives to land plants are in fact the Zygnematales. Dr Becker explained, "It seems that Zygnematales have lost oogamy and their ability to produce sperm and egg cells, and instead, possibly due to selection pressure in the absence of free water, use conjugation for reproduction. Investigation of such a large number of genes has shown that, despite their apparent simplicity, Zygnematales have genetic traces of other complex traits also associated with green land plants. Consequently Zygnematales true place as the closest living relative to land plants has been revealed." Media Contact Dr Hilary Glover Scientific Press Officer, BioMed Central Tel: +44 (0) 20 3192 2370 Email:
Embargoed until: 2:00 P.M., ESTDecember 13, 2001NSF PR 01-104 Media contact:Cheryl Dybas (703) 292-8070/[email protected] Program contact:James Rodman(703) 292-8481/[email protected] RESEARCHERS FIND CLOSEST LIVING RELATIVE OF FIRST LAND PLANTS Some 470 million years ago, the first land plants emerged from prehistoric waters, put down roots in soil and ended up ruling the plant world. But scientists haven't been certain about the family history of those pioneer plants. By studying gene sequences of common fresh water algae, a team of University of Maryland researchers, funded by the National Science Foundation (NSF) has traced this family tree and identified a group of algae that are the closest living relatives of the first land plants. The scientists have moved a step closer to understanding how land plants evolved and came to dominate the terrestrial biosphere. "What used to be a very short story - land plants evolved from aquatic algae - just became a much more interesting narrative," said James Rodeman, program director in NSF's division of environmental biology. "The new details in this part of the Tree of Life will guide research on how photosynthesizing organisms conquered the land." In a study published in the Dec. 14 issue of the journal Science, Maryland scientist Charles Delwiche and doctoral student Kenneth Karol confirm that the closest living relative of the first land plants is a group of green algae called the Charales, which survives today in fresh water around the world. "Science has long believed that land plants are derived from primeval algae that became adapted to live on land, but we weren't sure exactly how this happened, or which living algae were most closely related to land plants," said Delwiche. "It's an important part of the Tree of Life that has been unresolved." Although both the Charales and land plants can be traced back in the fossil record over a period of more than 400 million years, their common ancestor has been extinct for even longer and hasn't been identified in the fossil record. "Our data confirm that land plants and the Charales both evolved from a common ancestor that was a fairly complex organism," said Delwiche. "We now can make specific inferences about what this organism looked like. It wasn't just some sort of amorphous pond scum. It was made up of branching threads and reproduced with eggs and sperm." Scientists have thought that Charales and another group of algae called the Coleochaetales were almost equal cousins of the first land plants. Both groups share with land plants similar characteristics of growth, reproduction and cell division. But it wasn't until Delwiche and Karol, along with collaborator Richard M. McCourt at the Academy of Natural Sciences in Philadelphia and University of Maryland student Matthew T. Cimino, studied the DNA sequences of four genes from 40 different plants and algae that the lineage could be traced with certainty. "Plants didn't write diaries or letters for us to study, but they do have genetic sequences that can reveal their evolutionary history," said Karol. "The DNA of the Coleochaeteles shows many similar characteristics to land plants, but the Charales are even more closely related. The genes we examined show not only that the Charales are related to the first land plants, but that they are the closest living relatives." "These findings can help us understand what properties allowed land plants to dominate the biosphere," said Delwiche. "It's really exciting to know that we still have plants that look like the ancestors that were underfoot when the dinosaurs roamed the earth." The study was funded by the "Partnership for Enhancing Expertise in Taxonomy" program of the National Science Foundation. -NSF- It was previously thought that land plants evolved from stonewort-like algae. However, new research published in BioMed Central's open access journal BMC Evolutionary Biology shows that the closest relatives to land plants are actually conjugating green algae such as Spirogyra.
Ancestors of green plants began to colonise the land about 500 million years ago and it is generally accepted that they evolved from streptophyte algae (a group of green, fresh water algae). But this group of algae is very diverse and currently ranges from simple, one cell, flagellates to more complex, branching, algae such as stoneworts (Chara). It was thought that Charales were the closest relatives to land plants because they share (amongst other characteristics) a similar method of fertilisation, oogamy, with a large egg and small swimming sperm. For flowering plants this sperm is contained within pollen grains. In contrast, another type of streptophytes, the Zygnematales, use conjugation, a method of reproduction where the gametes are of equal size, isogamy, and one or both crawl, amoeba-like, into a fertilization tube where they meet and fuse. Some phylogenetic analysis had been done previously, on a smaller number of genes, which seemed to support the Charales theory. However, a multinational team, involving researchers in Germany and Canada, analysed genetic divergence in 129 genes from 40 different green plant taxa. This data showed that, despite the differences in reproductive strategy, the closest living relatives to land plants are in fact the Zygnematales. Dr Becker explained, "It seems that Zygnematales have lost oogamy and their ability to produce sperm and egg cells, and instead, possibly due to selection pressure in the absence of free water, use conjugation for reproduction. Investigation of such a large number of genes has shown that, despite their apparent simplicity, Zygnematales have genetic traces of other complex traits also associated with green land plants. Consequently Zygnematales true place as the closest living relative to land plants has been revealed."
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Published: March 10, 2011 Matthew Von Konrat, Head of Botanical Collections; McCarter Collections Manager, Bryophytes and Pteridophytes, Gantz Family Collections Center Alert
A rare collection of 13 publications in a broad-based botanical journal is solely dedicated to these remarkable early land plants. A recent issue of Phytotaxa is dedicated to a group of green land plants commonly referred to as bryophytes. A broad consensus confirms that bryophytes may not be monophyletic, but rather represent three paraphyletic lines, i.e., Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses). Together, bryophytes are the second largest group of land plants after flowering plants, and are pivotal in our understanding of early land plant evolution. A growing body of evidence is now supporting liverworts as the earliest diverging lineage of embryophytes, i.e., sister to all other groups of land plants. Bryophytes are important components of the vegetation in many regions of the world, constituting a major part of the biodiversity in moist forest, wetland, mountain and tundra ecosystems. Together, the three lineages, play a significant role in the global carbon budget and CO2 exchange, plant succession, production and phytomass, nutrient cycling and water retention. Bryophyte communities offer microhabitats that are critical to the survival of a tremendous diversity of organisms such as single-celled eukaryotes, protozoa and numerous groups of invertebrates. These groups of plants are also important environmental indicators and have been used as predictors of past climate change, to validate climate models and as potential indicators of global warming. The compilation of this volume can be attributed to a community effort and the high quality of papers is the product of all those who participated as reviewers, contributors and editorial support. In preparing for the volume, it became evident that the study of liverworts, hornworts, and mosses remains strong and has a healthy future as evidenced by contributions from senior scientists, post-doctoral researchers and doctoral students. We include 13 scientific papers from 35 authors. We hope the broad scope of papers will draw wide appeal and interest beyond the study of bryophytes. The papers include a broad array of disciplines and subjects, including biogeography, checklists and distribution, conservation, delimitation of species, fungal symbioses in bryophytes, molecular phylogenetics, species richness and systematics. The papers include a broad array of disciplines and subjects, including biogeography, checklists and distribution, conservation, delimitation of species, fungal symbioses in bryophytes, molecular phylogenetics, species richness and systematics. The entire issue is open access. |
What are the closest living relatives of land plants?
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