Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Hail to the hornworts: New plant family tree sheds light on evolution of life cycles

06.10.2006
In the history of life on earth, one intriguing mystery is how plants made the transition from water to land and then went on to diversify into the array of vegetation we see today, from simple mosses and liverworts to towering redwoods.

A research team led by University of Michigan evolutionary biologist Yin-Long Qiu has new findings that help resolve long-debated questions about the origin and evolution of land plants. The work will be published online this week in the Proceedings of the National Academy of Sciences.

Two major steps kicked off the chain of events that helped land plants prosper, forming the basis for modern land-based ecosystems and fundamentally altering the course of evolution of life on earth, said Qiu. The first step was the colonization of land by descendents of aquatic plants known as charophyte algae. That event opened up a vast new world where the sun's intensity was undiminished by passage through water and where carbon dioxide—another essential ingredient for plant life—was abundant.

The second event was a key change in plant life cycles. Plants exhibit a phenomenon known as alternation of generations, in which two alternating forms with different amounts of DNA make up a complete life cycle. One form, known as a sporophyte, produces spores, which grow into individuals of the other form, called gametophytes. Gametophytes produce gametes—eggs and sperm—which unite to form a fertilized egg capable of becoming a new sporophyte, thus completing a life cycle. While all plants exhibit alternation of generations, some spend most of their life cycle as sporophytes, and others spend more time in the gametophyte phase.

"Early in the history of plant evolution, a shift occurred," said Qiu, an assistant professor of ecology and evolutionary biology. "If you look at the so-called 'lower' plants such as algae, liverworts and mosses, they spend most of their life cycle as gametophytes. But if you look at plants like ferns, pines and flowering plants, they spend most of their time as sporophytes. Geneticists, developmental biologists and evolutionists have been wondering how the switch happened and have put forth two competing hypotheses."

For each hypothesis, scientists have come up with an evolutionary scheme showing how different plant lineages should be related to explain the generation shift. Studies over the last century have produced conflicting results on relationships among early land plant lineages, leaving unanswered the most critical question of how the shift in alternation of generations occurred. Qiu's group used three complementary sets of genetic data, involving more than 700 gene sequences, to resolve relationships among the four major lineages of land plants: liverworts, mosses, hornworts and vascular plants (which include ferns, pines and flowering plants). Their analysis showed that liverworts—tiny green, ribbon-like plants often found along river banks—represent the first lineage that diverged from other land plants when charophyte algae first came onto land, and an obscure group called hornworts, often found in abandoned corn fields, represents the progenitors of the vascular plants.

"Basically we captured a few major events that happened in the first few tens of millions of years of land plant evolution," Qiu said. The results make sense in light of the plants' life cycle patterns. Charophyte algae, liverworts and mosses spend most of the cycle in a free-living gametophyte phase; the sporophyte is a small, short-lived organism that lives on the gametophyte. Vascular plants, on the other hand, spend most of their time as free-living sporophytes, with small, short-lived, gametophytes that often live on the sporophytes. Hornworts may hold a clue to understanding how this shift happened, as they spend most of their life cycle in the gametophyte phase, but their sporophytes---unlike those of liverworts and mosses—show a tendency to become free-living.

Understanding evolutionary relationships among plant groups is crucial to understanding their biology, just as understanding relationships among primates advances our knowledge of human behavior, anatomy and physiology, Qiu said.

"As humans, we're always interested in knowing where we came from and why we are different from other primates," Qiu said. "Now that we know, from phylogenetic analyses, that our closest relative is the chimpanzee, we can compare the chimpanzee genome with our own genome and compare the chimpanzee brain with our own brain and compare chimpanzee behavior with human behavior.

But this all assumes we know the chimpanzee is our brother. What if we didn't know? Understanding evolutionary history really is the foundation of biology, and with today's emphasis on biofuels and medically important plants, it should be clear how important it is to learn the evolutionary history of all the organisms on our planet."

Qiu collaborated on the project with 20 other researchers from the University of Michigan; the University of Massachusetts, Amherst; the Chinese Academy of Sciences; Universitat Bonn in Germany; the University of Chicago; Southern Illinois University; the University of Akron in Ohio; Freie Universitat Berlin in Germany; Dresden University of Technology in Germany and Harvard University. The U.S. National Science Foundation, the National Natural Science Foundation of China and the Michigan Society of Fellows provided funding.

Nancy Ross-Flanigan | EurekAlert!
Further information:
http://www.umich.edu

Further reports about: Algae Evolutionary Qiu gametophyte hornworts lineage liverworts mosses sporophyte

More articles from Life Sciences:

nachricht Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY

nachricht NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>