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Insight Into Evolution Of First Flowers


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Bianca
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« on: May 19, 2009, 08:14:42 pm »








This flower from an avocado tree (Persea americana) shows the characteristics of ancient flowering-plant lineages. Its petals (colorful in most flowers) and sepals (usually a green outer layer) are combined into one organ.

A new study led by University of Florida researchers provides insight into how the first flowering plants emerged from non-flowering plants and began evolving about 130 million years ago.



(Credit:
Image courtesy of
University of Florida)
« Last Edit: May 19, 2009, 08:25:05 pm by Bianca » Report Spam   Logged

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Bianca
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« Reply #1 on: May 19, 2009, 08:21:33 pm »










                                          Insight Into Evolution Of First Flowers





ScienceDaily
(May 19, 2009)

Charles Darwin described the sudden origin of flowering plants about 130 million years ago as an abominable mystery, one that scientists have yet to solve.

But a new University of Florida study, set to appear in the online edition of the Proceedings of the National Academy of Sciences, is helping shed light on the mystery with information about what the first flowers looked like and how they evolved from nonflowering plants.

"There was nothing like them before and nothing like them since," said Andre Chanderbali, lead author of the study and a postdoctoral associate at UF's Florida Museum of Natural History. "The origin of the flower is the key to the origin of the angiosperms (flowering plants)."

The goal of this research is to understand the original regulatory program, or set of genetic switches, that produced the first flower in the common ancestor of all living flowering plants, said Pam Soltis, study co-author and curator of molecular systematics and evolutionary genetics at the Florida Museum. Better understanding of these genetic switches could one day help scientists in other disciplines such as medicine or agriculture, including help in growing plants used to fight disease or developing more drought-resistant crops.

The flower is one of the key innovations of evolution, responsible for a massive burst of evolution that has resulted in perhaps as many as 400,000 angiosperm species. Before flowering plants emerged, the seed-bearing plant world was dominated by gymnosperms, which have cone-like structures instead of flowers and include pine trees, sago palms and ginkgos. Gymnosperms first appeared in the fossil record about 360 million years ago.

The new study provides insight into how the first flowering plants evolved from pre-existing genetic programs found in gymnosperms and then developed into the diversity of flowering plants we see today.
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« Reply #2 on: May 19, 2009, 08:27:24 pm »









The study compares the genetic structure of two vastly different flowering plants to see whether differences exist in the set of circuits that create each species' flower. Researchers examined the genetic circuitry of Arabidopsis thaliana, a small flowering plant commonly used as a model organism in plant genetics research, and the avocado tree Persea americana, which belongs to an older lineage of so-called basal angiosperms.

"What we found is that the flower of Persea is a genetic fossil, still carrying genetic instructions that would have allowed for the transformation of cones into flowers," Chanderbali said.

Advanced angiosperms have four organ types: female organs (carpels), male organs (stamens), petals (typically colorful) and sepals (typically green). Basal angiosperms have three: carpels, stamens and tepals, which are typically petal-like structures. The researchers expected each type of organ found in Persea's flowers would have a unique set of genetic instructions. Instead they found significant overlap among the three organ types.

"Although the organs are developing to ultimately become different things, from a genetic developmental perspective, they share much more than you would expect," Chanderbali said. "As you go back in time, the borders fade to a blur."

"With these facts established, we can now think about the vast space open to natural selection to establish ever more rigid borders," said Virginia Walbot, a biology professor at Stanford University who is familiar with the research. The selection process arrived at a "narrow solution in terms of four discrete organs but with fantastic diversity of organ numbers, shapes and colors that provide the defining phenotypes of each flowering plant species."

Researchers don't know exactly which gymnosperms gave rise to flowering plants, but previous research suggests some genetic program in the gymnosperms was modified to make the first flower, Soltis said. A pine tree produces pine cones that are either male or female, unlike flowers, which contain both male and female parts. But a male pine cone has almost everything that a flower has in terms of its genetic wiring.

Douglas Soltis, chairman of the UF botany department, emphasized that the study highlights the importance of studying primitive flowering plants such as the avocado to gain insight into the early history of the flower. Survivors of ancient lineages represent a crucial link to the first flowers and provide insight that cannot be obtained by studying highly derived models such as Arabidopsis, he said.


--------------------------------------------------------------------------------

Journal reference:

1.Chanderbali et al. Transcriptional signatures of ancient floral developmental genetics in avocado (Persea americana; Lauraceae). Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0811476106
Adapted from materials provided by University of Florida.
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http://www.sciencedaily.com /releases/2009/05/090518172453.htm
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« Reply #3 on: May 19, 2009, 08:32:05 pm »



The Amborella plant.

(Photo by
Tom Lemieux)








                      South Pacific Plant May Be Missing Link In Evolution Of Flowering Plants






ScienceDaily
(May 17, 2006)

A new University of Colorado at Boulder study involving a "living fossil plant" that has survived on Earth for 130 million years suggests its novel reproductive structure may be a "missing link" between flowering plants and their ancestors.

The Amborella plant, found in the rain forests of New Caledonia in the South Pacific, has a unique way of forming eggs that may represent a critical link between the remarkably diverse flowering plants, known as angiosperms, and their yet to be identified extinct ancestors, said CU-Boulder Professor William "Ned" Friedman. Angiosperms are thought to have diverged from gymnosperms -- the dominant land plants when dinosaurs reigned in the Cretaceous and Jurassic periods -- roughly 130 million years ago and have become the dominant plants on Earth today.

"One of the biggest challenges for evolutionary biologists is understanding how these flowering plants arose on Earth," said Friedman, a professor in CU-Boulder's ecology and evolutionary biology department, whose study appears in the May 18 issue of Nature. "The study shows that the structure that houses the egg in Amborella is different from every other flowering plant known, and may be the potential missing link between flowering plants and their progenitors."

In basic terms, Amborella has one extra sterile cell that accompanies the egg cell in the female part of its reproductive apparatus known as the embryo sac, according to the study. The discovery of the unique configuration of the egg apparatus, which is thought to be a relic of intense evolutionary activity in early angiosperm history, "is akin to finding a fossil amphibian with an extra leg," according to a May 18 Nature perspective piece accompanying Friedman's article.

The novel embryo sac described in Nature is the first new type of egg-bearing apparatus to be discovered in flowering plants in more than 50 years, according to Friedman. "The unique four-celled egg apparatus in Amborella could represent a critical link between angiosperms and gymnosperms," he wrote in Nature.

The study was funded by the National Science Foundation.

The origin and evolution of flowering plants has long confounded scientists, he said. Nearly 130 years ago, Charles Darwin, known for developing the theory of natural selection, called the appearance of flowering plants "an abominable mystery."

The surprising new finding suggests flowering plants may have arisen on Earth during a time when plant evolution was "particularly flexible," Friedman said.

The peculiar egg-forming structure seen in Amborella may eventually link the odd South Pacific shrub to gymnosperms such as conifers, said Friedman. "We associate this structure with a relatively primitive reproductive process," he said.

Amborella is a small shrub with tiny greenish-yellow flowers and red fruit that grows only in the understory of New Caledonia rain forests. Amborella plants are unisexual, meaning they will produce either all male or female flowers. Cross-pollination between plants is required for fruit production.

Plants used in the study were from both New Caledonia and from specimens cultivated in a CU-Boulder greenhouse. Friedman used a combination of laser, fluorescence and electron microscope techniques during the study.

"My research and teaching go hand in hand, and this is the kind of science that goes directly into the classroom," said Friedman, who oversees the work of six CU-Boulder undergraduates and graduate students. "The kinds of discoveries we make in the lab have a profound effect on the material taught in my courses."

Friedman, who also is a co-investigator at CU-Boulder's Astrobiology Center, directs several NSF-funded research efforts. He is the chief scientist for NSF's Molecular and Organismic Research in Plant History, or MORPH project that supports training opportunities around the country for students, postdoctoral fellows and early career professionals. MORPH focuses on the diversification of plant forms on Earth over the past 500 million years.


--------------------------------------------------------------------------------

Adapted from materials provided by University of Colorado at Boulder.
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 MLA University of Colorado at Boulder (2006, May 17). South Pacific Plant May Be Missing Link In Evolution Of Flowering Plants. ScienceDaily. Retrieved May 19, 2009, from



http://www.sciencedaily.com /releases/2006/05/060517181205.htm
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« Reply #4 on: May 19, 2009, 08:38:07 pm »








Phylogenetic relationships among the major lineages of flowering plants based on plastid genome sequences.

Pictured counter-clockwise from the root at the base of the circle tree are:



Amborella trichopoda,

Nymphaea odorata,

Illicium floridanum,

Chloranthus angustifolius,

Piper longum,

Liriodendron tulipifera,

Ceratophyllum demersum,

Ranunculus ficaria,

Pelargonium exstipulatum,

Helianthus annuus,

Yucca filamentosa,

Triticum aestivum, and

Acorus americanus.



New Caledonia, home to Amborella trichopoda, is shown in the background. (Credit: Gwen Gage)
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« Reply #5 on: May 19, 2009, 08:45:12 pm »










                                  Flowering Plants Evolved Very Quickly Into Five Groups






ScienceDaily
(Nov. 27, 2007)

University of Florida and University of Texas at Austin scientists have shed light on what Charles Darwin called the "abominable mystery" of early plant evolution.

The scientists are reporting that the two largest groups of flowering plants are more closely related to each other than any of the other major lineages. These are the monocots, which include grasses and their relatives, and the eudicots, which include sunflowers and tomatoes.

Doug and Pam Soltis, a UF professor of botany and curator at UF's Florida Museum of Natural History, respectively, also showed that a stunning diversification of flowering plants they are referring to as the "Big Bang" took place in the comparatively short period of less than 5 million years -- and resulted in all five major lineages of flowering plants that exist today.

"Flowering plants today comprise around 400,000 species," said Pam Soltis. "So to think that the burst that give rise to almost all of these plants occurred in less than 5 million years is pretty amazing -- especially when you consider that flowering plants as a group have been around for at least 130 million years."

The lead author of the UF paper is Michael Moore, a former postdoctoral associate in the Soltis lab and current faculty member at Oberlin College. Charles Bell, the fourth author, is another former Soltis postdoctoral associate, now at the University of New Orleans.

Robert Jansen, professor of integrative biology at The University of Texas at Austin, said the two papers set the stage for all future comparative studies of flowering plants.

"If you are interested in understanding the evolution of flowering plants, you can't do that unless you understand their relationships," he said.

Botanists predating Darwin have long recognized that flowering plants, which comprise at least 60 percent of all green plant species, diversified abruptly shortly after they appeared.

The details, and especially the cause of, this diversification -- Darwin's "abominable mystery" -- has been a hot topic in botany ever since.

"One of the reasons why it's been hard to understand evolutionary relationships among the major groups of flowering plants is because they diversified over such a short time frame," Jansen said.

Seeking to distill the cloudy picture into a clear one, the UF and UT researchers analyzed DNA sequences from the completely sequenced genomes of the chloroplast. That organelle, responsible for plants' ability to photosynthesize, is shared by all green plants.

Jansen and his UT Austin colleagues analyzed DNA sequences of 81 genes from the chloroplast genome of 64 plant species, while the UF researchers analyzed 61 genes from 45 species. The two groups also performed a combined analysis, which produced evolutionary trees that included all the major groups of flowering plants.

The analyses also confirmed that a unique species of plant called Amborella, found only on the Pacific island of New Caledonia, represents the earliest diverging lineage of flowering plants.

By laboriously arranging the sequences, the researchers slowly built a kind of family tree for plants -- a diagram of relationships among plant lineages showing diversification over the eons. Based on known rates of genetic change double-checked against fossils of known ages, they established a time scale that revealed the dates of major branching events.

Based on the Soltises' and their collaborators' research in previous years, it was known that flowering plants split into three branches shortly after they appeared about 130 million years ago. That process was relatively gradual, at least compared with the rapid radiation that happened next. The details of that radiation have long been murky. The latest research clears the picture by showing that all plants fall into five major lineages that developed over the relatively short period of 5 million years, or possibly even less.

As for the diversification's cause, it remains mysterious, Pam and Doug Soltis said.

It's possible it was spurred by some major climatic event. It's also possible that a new evolutionary trait -- a water-conducting cell that transfers water up plant stems -- proved so effective that it spurred massive plant species diversification. The cell is either not present, or is poorly developed, in the first three flowering plant lineages, Doug Soltis said. The earliest flowering plant lineages also did not have a completely fused ovary, which in later flowering plants may better protect the seeds, Pam Soltis said.

Two papers on this research are set to be published in the beginning of December in the Proceedings of the National Academy of Sciences.


--------------------------------------------------------------------------------

Adapted from materials provided by University of Florida,
via EurekAlert!,
a service of AAAS.
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« Reply #6 on: May 19, 2009, 08:47:26 pm »








This image shows pollen tubes extending from grains of pollen in the rare vine Austrobaileya.

University of Tennessee, Knoxville, researcher Joe Williams found that the tubes' ability to grow quickly played a major role in the evolution of the large variety of flowering plants.



(Credit:
Joe Williams/
University of Tennessee,
Knoxville)
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« Reply #7 on: May 19, 2009, 08:51:54 pm »









                                    Unexpected Key To Flowering Plants' Diversity






ScienceDaily
(July 29, 2008)

What began with an off-the-cuff curiosity eventually led Joe Williams to hang from the limbs of a tree 80 feet above the soil of northeastern Australia.

The things Williams, a University of Tennessee, Knoxville, researcher found there may help explain the amazing diversity in the world's flowering plants, a question that has puzzled scientists from the time of Charles Darwin to today.

Williams' findings, published online this week by the Proceedings of the National Academy of Sciences, show that the ability of flowering plants -- known as angiosperms -- to quickly and efficiently move sperm from pollen to egg through a part of the plant was the key to their evolutionary diversity.

His curiosity was based in the time it takes from when pollen lands on a plant to the time that its' seed is fertilized. Williams noticed a recurring theme in the research papers he read:

"They would usually describe how fertilization was occurring, but they never tell you much about timing," said Williams, an assistant professor of ecology and evolutionary biology at UT Knoxville.

For a seeded plant to fertilize, pollen that lands on the flower must grow a tube to carry sperm to the egg. In non-flowering plants, the pathway is usually short, because the pollen tube must destroy cells in its path, which is a time-consuming process. In flowering plants, though, pollen tubes are able to cover longer distances to the egg by essentially "squeezing" between cells. It is a trait that Williams says is vital to their diversification.

"The longer a plant takes to fertilize, for the pollen to reach the egg," said Williams, "the more chance there is for it to die."

When he studied the data he had collected through the years, Williams found that older lineages of flowering plants -- those on lower branches of the angiosperms' evolutionary family tree -- grew shorter tubes of pollen than those that went on to evolve into the diverse array of flowering plants that exist today.

That's what brought Williams to a harness in the rainforest of Australia. To confirm what he found in the data analysis, he pollinated -- by hand -- an ancient vine known as Austrobaileya that grows high in the canopy. He chose that plant, along with another plant found only on the Pacific island of New Caledonia and a water lily that grows high in the Colorado mountains, to test because they developed as species early in flowering plants' evolution.

He found that, when compared to more recently evolved species of angiosperms, the older plants grew shorter pollen tubes and took longer to do so than more diverse modern species. According to Williams, this indicates that these pollen tubes likely played a previously unknown role in spurring the evolution of the roughly 250,000 species of flowering plants we see today.

"As these plants gained the ability to grow pollen tubes faster and over longer distances," said Williams, "It gave them the ability to develop the much larger and more complex flowers as well as deeper ovaries with more seeds -- that is to say, larger fruits -- that we see around us today."

Williams' work was funded by UT Knoxville and the National Science Foundation.


--------------------------------------------------------------------------------

Adapted from materials provided by University of Tennessee at Knoxville, via EurekAlert!, a service of AAAS.
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 MLA University of Tennessee at Knoxville (2008, July 29). Unexpected Key To Flowering Plants' Diversity. ScienceDaily. Retrieved May 19, 2009, from



 http://www.sciencedaily.com /releases/2008/07/080728192946.htm
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