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 For a chimpanzee, one good turn deserves another
27.06.2017 | Max-Planck-Institut für Mathematik in den Naturwissenschaften (MPIMIS)

nachricht New method to rapidly map the 'social networks' of proteins
27.06.2017 | Salk Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>