Fungus and bees help orchids diversify


Scientists have discovered why orchids are one of the most successful groups of flowering plants – it is all down to their relationships with the bees that pollinate them and the fungi that nourish them.

The orchid family is one of the largest groups of flowering plants, with over 22,000 species worldwide. Today’s research suggests that there is such a huge range of species because orchids are highly adaptable and individual species can interact with bees, and other pollinators, in different ways.

For example, when orchids Pterygodium pentherianum and Pterygodium schelpei live side by side, Pterygodium pentherianum puts its pollen on the bee’s front legs, whereas Pterygodium schelpei puts it on the bee’s abdomen. This means that one bee can carry pollen from two distinct species without mixing it.

The study also shows how orchids are able to live harmoniously together, with different species working in partnership with different microscopic fungi in the soil, ensuring they do not compete with each other.

Prior to today’s study, it was known that orchids have strong interactions with bees, which pollinate the flowers in return for food such as nectar or oils, and also with fungi, which supply minerals to the roots in return for sugars. These relationships are amongst the best examples of nature’s system of ‘mutual benefit’ and are believed to have been important for enabling orchids to evolve into so many different species. However, the mechanisms by which these relationships affect the number of plant species, and these species’ ability to coexist, had remained obscure.

The group studied 52 orchid species in a small region of South Africa, which all secrete oil inside their flowers that female bees collect to feed to their larvae. In order to investigate which pollinating bees were visiting the different species, they collected orchid pollen from the bees for DNA sequencing and analysis. They found strong evidence that when an orchid moved to a new geographical area it adapted to a different pollinating bee species, and interestingly, some competing orchid species were able to adapt by placing pollen on different body parts of the same bee.

“What is remarkable in these orchids is that diversity is generated not only through switches between bees, but also by switches between different body parts of the same bee, so two closely related orchids might place pollen on different segments of one bee’s front leg,” added Professor Barraclough. “It’s given us a fundamental insight into how so many new species can originate, and once they originate how they are able to coexist without exchanging genes.”

The researchers also studied the microscopic fungi living on the roots of the orchid, to see how this relationship was affecting plant diversity. Most flowering plants host microscopic fungi in their roots that help the plant take up nutrients from the soil. Until now it has been difficult to investigate this interaction, as most of the fungi belong to species that are difficult to culture. The researchers overcame this challenge by combining a molecular technique known as DNA barcoding with field experiments. In contrast to the bees, where co-occurring orchid species normally share the same insect pollinator, the plants needed to use different fungal partners in order to coexist in the same region.

“By tapping into different kinds of fungi, different plant species access different pools of nutrients and so the problem of living together without competing for the same resources is solved,” said Professor Barraclough. However, the same fungal partners are found in different geographical areas and so orchid species that originate in different areas, by adapting to different pollinators, tend still to use the same fungi.

The team’s fieldwork shows that shifts in pollination traits were important for bringing about new species and allowing coexistence in a diverse group of orchids, whereas shifts in fungal partner were important for coexistence but not for speciation. Many other groups of flowering plants enter into similar relationships with pollinators and fungi, and both the origins and the future survival of that diversity could depend critically on understanding these relationships.

source

The Effects of Above- and Belowground Mutualism on Orchid Speciation and Coexistence

Orchid lives its life underground

Rhizanthella gardneri is a cute, quirky and critically endangered orchid that lives all its life underground. It even blooms underground, making it virtually unique amongst plants.

Last year, using radioactive tracers, scientists at The University of Western Australia showed that the orchid gets all its nutrients by parasitising fungi associated with the roots of broom bush, a woody shrub of the WA outback.

Now, with less than 50 individuals left in the wild, scientists have made a timely and remarkable discovery about its genome.

Despite the fact that this fully subterranean orchid cannot photosynthesise and has no green parts at all, it still retains chloroplasts – the site of photosynthesis in plants.

“We found that compared with normal plants, 70 per cent of the genes in the chloroplast have been lost,” said Dr Etienne Delannoy, of the ARC Centre for Excellence in Plant Energy Biology, the lead researcher of a study published in Molecular Biology and Evolution. “With only 37 genes, this makes it the smallest of all known plant chloroplast genomes.”

“The chloroplast genome was known to code for functions other than photosynthesis, but in normal plants, these functions are hard to study,” said ARC Centre Director Professor Ian Small.

“In Rhizanthella, everything that isn’t essential for its parasitic lifestyle has gone. We discovered that it has retained a chloroplast genome to make only four crucial proteins.

Our results are relevant to understanding gene loss in other parasites, for example, the Plasmodium parasite that causes malaria.”

Associate Professor Mark Brundrett from the Wheatbelt Orchid Rescue Project describes Rhizanthella as one of the most beautiful, strange and iconic orchids in the world.

“Combining on-the-ground conservation efforts with cutting edge laboratory technologies has led to a great discovery with impacts for both science and conservation. The genome sequence is a very valuable resource, as it makes it possible to estimate the genetic diversity of this Declared Rare plant”.

Professor Brundrett has been working with the Department of Environment and Conservation and volunteers from the West Australian Native Orchid Study and Conservation Group to locate these unique orchids.

“We needed all the help we could get since it often took hours of searching under shrubs on hands and knees to find just one underground orchid!”
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Why do plants with too little light get leggy?

In short: Plants measure the amount of red and blue light reaching their leaves. When that light falls to too low of a level the plant releases hormones which allow it to shoot up past the plants around it so it may get more light.

OLYMPUS DIGITAL CAMERA

Plants grow in dense vegetations at the risk of being out-competed by neighbors. To increase their competitive power, plants display adaptive responses, such as rapid shoot elongation (shade avoidance) to consolidate light capture.

These responses are induced upon detection of proximate neighbors through perception of the reduced ratio between red (R) and far-red (FR) light that is typical for dense vegetations. The plant hormone auxin is a central regulator of plant development and plasticity, but until now it has been unknown how auxin transport is controlled to regulate shade-avoidance responses.

Here, we show that low R:FR detection changes the cellular location of the PIN-FORMED 3 (PIN3) protein, a regulator of auxin efflux, in Arabidopsis seedlings. As a result, auxin levels in the elongating hypocotyls are increased under low R:FR. Seedlings of the pin3-3 mutant lack this low R:FR-induced increase of endogenous auxin in the hypocotyl and, accordingly, have no elongation response to low R:FR.

We hypothesize that low R:FR-induced stimulation of auxin biosynthesis drives the regulation of PIN3, thus allowing shade avoidance to occur. The adaptive significance of PIN3-mediated control of shade-avoidance is shown in plant competition studies. It was found that pin3 mutants are outcompeted by wild-type neighbors who suppress fitness of pin3-3 by 40%. We conclude that low R:FR modulates the auxin distribution by a change in the cellular location of PIN3, and that this control can be of great importance for plants growing in dense vegetations. paper

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’.
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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

Venus Flytraps are even creepier than we thought

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