What pine cones reveal about the evolution of flowers

From southern Africa’s pineapple lily to Western Australia’s swamp bottlebrush, flowering plants are everywhere. Also called angiosperms, they make up 90 percent of all land-based, plant life.

New research published this week in the Proceedings of the National Academy of Sciences provides new insights into their genetic origin, an evolutionary innovation that quickly gave rise to many diverse flowering plants more than 130 million years ago. Moreover, a flower with genetic programming similar to a water lily may have started it all.

“Water lilies and avocado flowers are essentially ‘genetic fossils’ still carrying genetic instructions that would have allowed the transformation of gymnosperm cones into flowers,” said biologist Doug Soltis, co-lead researcher at the University of Florida in Gainesville.

Gymnosperms are a group of seed-bearing plants that include conifers and cycads that produce “cones” as reproductive structures, one example being the well-known pine cone. “We show how the first flowering plants evolved from pre-existing genetic programs found in gymnosperm cones and then developed into the diversity of flowering plants we see today,” he said. “A genetic program in the gymnosperm cone was modified to make the first flower.”

But, herein is the riddle. How can flowers that contain both male and female parts develop from plants that produce cones when individual cones are either male or female? The solution, say researchers, is that a male gymnosperm cone has almost everything a flower has in terms of its genetic wiring.

Somehow a genetic change took place allowing a male cone to produce female organs as well–and, perhaps more importantly, allowed it to produce showy petal-like organs that enticed new interactions with pollination agents such as bees.

Analyzing genetic information encoded in a diverse array of evolutionarily distant flowers–water lily, avocado, California poppy and a small flowering plant frequently used by scientists as a model, Arabidopsis–researchers discovered support for the single cone theory.

A non-flowering seed plant, a cycad named Zamia, which makes pine cone-like structures instead of flowers, was also examined in the study.

“We extracted an essential genetic material, RNA, from the flowers’ specific floral organs and in the case of Zamia, its cones, to see which genes were active,” said co-lead investigator Pam Soltis, a curator at the Florida Museum of Natural History and an evolutionary geneticist at the University of Florida.

Researchers then compared the organs’ profiles to a range of species representing ancient and more recent lineages of flowering plants. “This comparison allowed us to see aspects of the floral genetic program that are shared with gymnosperms, where they came from and also which aspects are shared among different groups of flowering plants and which differ,” she explained.

The flowers of most angiosperms have four distinct organs: sepals, typically green; petals, typically colorful; stamens, male organs that produce pollen; and carpels, female organs that produce eggs. However, the flowers of more ancient lineages of angiosperms have organs that intergrade, or merge into one another through a gradual series of evolutionary reforms. For example, a stamen of a water lily produces pollen but it may also be petal-like and colorful and there is often no distinction between sepals and petals–instead, early flowers have organs called tepals.

The research team found a very significant degree of genetic overlap among intergrading floral organs in water lilies and avocado but less overlap in poppy and Arabidopsis. “In other words, the boundaries between the floral organs are not all that sharp in the early angiosperm groups-the organs are still being sorted out in a sense,” said Doug Soltis.

The finding challenged researcher expectations that each floral organ in early angiosperms would have a unique set of genetic instructions as is the case in the evolutionarily derived Arabidopsis. Instead, the finding increased the likelihood that a single male cone was responsible for the world’s first flowering plants owing to the elasticity of their genetic structure.

“In early flowers, a stamen is not much different genetically speaking than a tepal,” said Doug Soltis. “The clearly distinct floral organs we all know and love today came later in flowering plant evolution–not immediately.”

Researchers say better understanding of these genetic switches in early angiosperm flowers could one day help scientists in other disciplines such as medicine or agriculture.

This project was conducted in collaboration with scientists at Penn State University, University at Buffalo, University of Georgia, and Fudan University in Shanghai, China. It was funded in part by the National Science Foundation’s Directorate of Biological Sciences.

-NSF- source

New Species of Carnivorous Plant found


A new species of carnivorous pitcher plant has been found by Fauna & Flora International (FFI) in Cambodia’s remote Cardamom Mountains.

The discovery of Nepenthes holdenii is an indicator of both the stunning diversity and lack of research in the forests of the Cardamom Mountains.

The large red and green pitchers that characterize Nepenthes holdenii are actually modified leaves designed to capture and digest insects. The pitchers can reach up to 30 cm long. The carnivorous strategy allows the plants to gain additional nutrients and flourish in otherwise impoverished soils.

A further unusual adaptation seen in this new species is its ability to cope with fire and extended periods of drought. Cambodia’s dry season causes forests to desiccate and forest fires are common.

Nepenthes holdenii exploits the clearings caused by these regular blazes by producing a large underground tuber which sends up a new pitcher-bearing vine after the fires have passed.

British photographer Jeremy Holden, who first found the plant on the FFI survey and after whom it is named, said: ‘The Cardamom Mountains are a treasure chest of new species, but it was a surprise to find something as exciting and charismatic as an unknown pitcher plant’.

This discovery is the latest in a series of new species described from the Cardamom Mountains, including a green-blooded frog and a number of new reptiles.

Jenny Daltry, FFI Senior Conservation Biologist said: ‘The flora of Cambodia is still poorly known and potentially holds many new species for researchers to discover’.
source

Venus flytrap chemical triggers discovered

Venus FlyTrap

The Venus flytrap has a “memory”. In order to avoid reacting to a “false alarm”, the plant does not snap shut at the first touch of the sensory hairs. Instead, there must be at least two stimulations of the hairs within 30 seconds. After that, the trap closes fast so that the prey cannot make a last-gasp escape. How does the trap’s memory work? The hypothesis is that certain messenger chemicals are released every time the hairs are stimulated, and these substances accumulate in the trap. Only when these substances reach a certain threshold concentration does an ion channel open – like the mechanism used to transmit signals in our nerve cells—producing an action potential that allows the leaves of the trap to shut.

The trap snaps shut

Trap closing chemical factors

Researchers isolate the substance that causes Venus Flytraps to close

100 Million year old mutation leads to sex differentiation


Research by University of Leeds plant scientists has uncovered a snapshot of evolution in progress, by tracing how a gene mutation over 100 million years ago led flowers to make male and female parts in different ways.

The findings — published in the Proceedings of the National Academy of Sciences (PNAS) Online Early Edition — provide a perfect example of how diversity stems from such genetic ‘mistakes’. The research also opens the door to further investigation into how plants make flowers — the origins of the seeds and fruits that we eat.

In a number of plants, the gene involved in making male and female organs has duplicated to create two, very similar, copies. In rockcress (Arabidopsis), one copy still makes male and female parts, but the other copy has taken on a completely new role: it makes seed pods shatter open. In snapdragons (Antirrhinum), both genes are still linked to sex organs, but one copy makes mainly female parts, while still retaining a small role in male organs — but the other copy can only make male.

“Snapdragons are on the cusp of splitting the job of making male and female organs between these two genes, a key moment in the evolutionary process,” says lead researcher Professor of Plant Development, Brendan Davies, from Leeds’ Faculty of Biological Sciences. “More genes with different roles gives an organism added complexity and opens the door to diversification and the creation of new species.”

By tracing back through the evolutionary ‘tree’ for flowering plants, the researchers calculate the gene duplication took place around 120 million years ago. But the mutation which separates how snapdragons and rock cress use this extra gene happened around 20 million years later.

The researchers have discovered that the different behaviour of the gene in each plant is linked to one amino acid. Although the genes look very similar, the proteins they encode don’t always have this amino acid. When it is present, the activity of the protein is limited to making only male parts. When the amino acid isn’t there, the protein is able to interact with a range of other proteins involved in flower production, enabling it to make both male and female parts.

“A small mutation in the gene fools the plant’s machinery to insert an extra amino acid and this tiny change has created a dramatic difference in how these plants control making their reproductive organs,” says Professor Davies. “This is evolution in action, although we don’t know yet whether this mutation will turn out to be a dead end and go no further or whether it might lead to further complexities.

“Our research is an excellent example of how a chance imperfection sparks evolutionary change. If we lived in a perfect world, it would be a much less interesting one, with no diversity and no chance for new species to develop.”

The researchers now plan to study the protein interactions which enable the production of both male and female parts as part of further investigation into the genetic basis by which plants produce flowers. source 1, source 2, source 3

Single amino acid change alters the ability to specify male or female organ identity
Mutant snapdragons revealing the secret life of plants

Bees prefer stripes

All else being equal red and striped flowers attract more bees, at least in snapdragons.


Nuffield Bursary students spent successive summers observing the foraging patterns of bumblebees on snapdragon plants grown on a plot near Norwich. The students compared the number of visits by bumblebees to various cultivars of the common snapdragon and the number of flowers visited per plant. Red flowers and those with venation patterning were visited significantly more frequently than white or pink. More flowers were visited per plant too.

“Stripes provide a visual guide for pollinators, directing them to the central landing platform and the entrance to the flower where the nectar and pollen can be found,” said Professor Martin.

“We examined the origin of this trait and found that it has been retained through snapdragon ancestry. The selection pressure for this trait is only relaxed when full red pigmentation evolves in a species.”

Bumblebees are the main pollinators for snapdragon because the weight of the bee is needed to open the closed flower. Pollinators learn and memorize floral signals, such as flower shape, scent, colour and patterns of pigmentation. They return to flowers from which they have previously found food. Simple changes due to single gene changes can have dramatic effects on which pollinators visit and how often.

Using phylogenetics to detect pollinator-mediated floral evolution

Tallow tree continues its rapid spread through Gulf Coast

I know every year I’m here in The Woodlands I see more and more tallow trees appearing in parks and other wooded areas.

A study by a USDA Forest Service Southern Research Station scientist shows the numbers of nonnative Chinese tallowtree in Louisiana, Mississippi and east Texas grew by about 370 percent over a 16-year period. The spread of the invasive plant may create problems for plants and wildlife along the Gulf coast.

Tallowtree is a deciduous plant with heart-shaped leaves that grows to 60 feet in height. It invades stream banks, riverbanks, and wet areas like ditches as well as upland sites. Large seeds containing oil are spread by numerous large bird species. The tree is native to China and was introduced to South Carolina in the 1700s. There are approximately 457,000 acres of tallowtree in nine of the 13 southern states. Experts say tallowtree can change the chemical properties of soil and alter the composition and structure of native plant communities. Additionally, litter from the plant may alter habitat in invaded wetland areas, which could affect some frog and other amphibian species.

From 1994 to 2006, the number of tallowtree plants increased by 445 percent in Mississippi. In east Texas, the number increased by 174 percent between 1992 and 2007.

Jim Miller, a Forest Service ecologist and leading expert on invasive plants in the South, says the expansion of tallowtree in Louisiana, Mississippi and east Texas could adversely affect flora and fauna along the Gulf of Mexico and beyond.

“This is the first report to show how infestations are composed of thousands of small stems per acre that tightly grip lands in a near monoculture, excluding diversity with little potential for wood resource value,” said Miller. “The crisis is worsened by the plant’s rapid occupation of the highly diverse wetland prairies and marshes in east Texas and Louisiana, which are special habitats for many rare plants and animals and often productive native grasslands.”

Tallowtree is moderately difficult to control, but Miller says there is a new herbicide that targets the species specifically and leaves most other native trees and plants unharmed. He says landowners can help prevent the spread of tallowtree by not purchasing and planting the tree for ornamental or other purposes. Miller encourages landowners who already have tallowtree on their property to remove the tree and replace it with native species. He says landowners can work with a consulting forester to develop a control or prevention program if the species threatens to spread onto a landowner’s property. Miller believes organization of a coordinated tallowtree management program among impacted states is needed to safeguard the biosecurity of southern and eastern forests.

Miller believes the rapid spread of tallowtree poses a serious threat to the diversity and productivity of the South’s forests. He says as temperatures rise because of climate change, the probability of tallowtree moving farther north increases. Miller adds that bird-carried seed and ornamental plantings by unsuspecting homeowners will likely contribute to the northward spread of tallowtree. source

Invasion of tallow tree into southern US forests: influencing factors and implications for mitigation

Wasps battle wasps over wiliwili and coral bean trees


A black, two-millimeter-long wasp from East Africa is helping wage war on one of its own kind—the Erythrina gall wasp, an invasive species that’s decimated Hawaii’s endemic wiliwili (Erythrina sandwicensis) and introduced coral bean trees (Erythrina spp.).

Hawaii Department of Agriculture (HDOA) officials “recruited” the beneficial wasp, Eurytoma erythrinae, and first released it in November 2008 after evaluating its host specificity as a biocontrol agent. U.S. Department of Agriculture (USDA) entomologist Michael Gates’ scientific description and naming of the species, together with a collaborator, helped HDOA obtain the necessary federal approvals to make the release.

Female E. erythrinae wasps deposit their eggs inside galls where the pest larvae feed. Upon hatching, E. erythrinae larvae eat the gall wasp larvae. They pupate and emerge two weeks later as adults. The parasites don’t attack native wasps or other nontarget insects.

The HDOA found its “gall wasp gladiator” after dispatching two entomological teams to the pest’s native Africa in search of natural enemies, starting in spring 2006. In January 2007, Gates and Delvare were asked to identify the specimens collected based on their taxonomic expertise.

Gall-wasp parasitism has been as high as 70 percent at some release sites, but continued data collection will be necessary to correlate E. erythrinae’s rise to declines in tree damage.
Wasps wage war on behalf of Wiliwili trees

More information
Hawaii hosts wasp on wasp battle royale