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Research identifies mechanism that helps plants fight bacterial infection

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A team led by a plant pathologist at the University of California, Riverside, has identified a regulatory, genetic mechanism in plants that could help fight bacterial infection.

“By better understanding this molecular mechanism of regulation, we can modify or treat crops to induce their immune response against bacterial pathogens,” said Hailing Jin, a professor of microbiology and plant pathology, who led the research.

Working on Arabidopsis thaliana, a small flowering plant widely used by biologists as a model species, Jin’s research team found that Argonaute protein, a major core protein in the RNA interference machinery, is controlled by a process called “post-translational modification” during bacterial infection.

This process controls the level of the Argonaute protein and its associated small RNAs — molecules that regulate biological processes by interfering with gene expression. This provides double security in regulating the RNA interference machinery. RNA interference, or RNAi, is an important cellular mechanism that many organisms use to regulate gene expression. It involves turning off genes, also known as “gene silencing.”

A previous study in Jin’s lab identified that one of 10 Argonaute proteins in Arabidopsis is induced by bacterial infection and contributes to plant immunity — the higher the level of the protein, the higher the plant immunity. A high level of the protein, however, can limit the plant’s growth.

Under normal plant growth conditions, the Argonaute protein and its associated small RNAs are well controlled by arginine methylation – a type of post-translational modification of the Argonaute protein. This regulates the Argonaute protein and prevents it from accumulating to high levels. The small RNAs associated with the Argonaute protein are also prevented from accumulating to higher levels, allowing the plant to save energy for growth.

During bacterial infection, however, arginine methylation of the Argonaute protein is suppressed, which leads to the accumulation of the Argonaute protein and its associated small RNAs that contribute to plant immunity. Together, these two changes allow the plant to both survive and defend itself.

“If the Argonaute protein and the associated small RNAs were to remain at such high levels after normal conditions returned, it would be detrimental to plant growth,” Jin said. “But post-translational modification of the Argonaute protein, restored under normal conditions, decreases these levels to promote plant growth.”

Study results appear in Nature Communications.

Jin explained that all plants possess the RNAi machinery, as well as the equivalent plant-immunity-related Argonaute protein. RNA silencing is seen in all mammals, plants, and most eukaryotes.

“Until our study, how the Argonaute protein got controlled during a pathogen attack was unclear, and just how plants’ immune responses got regulated by the RNAi machinery was largely a mystery,” said Jin, who holds the Cy Mouradick Endowed Chair at UCR and is a member of UCR’s Institute for Integrative Genome Biology. “Ours is the first study to show that post-translational modification regulates the RNAi machinery in plant immune responses.”

Jin was joined in the study by UCR’s Po Hu, Hongwei Zhao, Pei Zhu, Yongsheng Xiao, Weili Miao, and Yinsheng Wang.

Read the paper: Nature Communications

Article source:University of California – Riverside

Image credit: Alexey Kuzmin in Pixabay

How Capsella followed its lonely heart

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The Brassicaceae plant family boasts a stunning diversity of fruit shapes. But even in this cosmopolitan company the heart-shaped seed pods of the Capsella genus stand out.

An estimated 8 million years ago Capsella embarked on a different evolutionary pathway from its close relatives Arabidopsis and Camelina.

This led to radically different shapes in the fruits which in these plants form pods that enclose the seeds prior to dispersal or dehiscence. Arabidopsis fruits are cylindrical, Camelina’s are spherical, while Capsella conspicuously follows its own heart.

Most of the diversity in the Brassicaceae occurs in one part of the fruit called the valves or seed pod walls. But until now it was not clear which mechanisms lay behind these differences.

Research, published in the journal Current Biology uncovers key processes involved in this genetic journey and offers evidence as to how and why these shapes occur.

The team from the John Innes Centre used gene-editing technology, transgenic plants and molecular reporting techniques to show that a well characterised gene called INDEHISCENT (IND) lay at the heart of the matter.

In the model plant Arabidopsis, this gene is locally expressed only in strips of cells that regulate seed dispersal or pod shatter.

In Capsella, experiments here show that IND has expanded its local expression into the upper part of the valves, the shoulders that give the plant its characteristic heart shaped fruits. Gene-edited mutant lines without the IND gene showed significantly reduced shoulders compared to the wild type.

Previous studies showed that IND regulates the plant growth hormone auxin. Here the team used two reporter genes with fluorescent tags which highlighted distinct spots or maxima of auxin at the twin shoulders of Capsella’s heart-shaped pods. However, these maxima were absent in plants without IND activity.

“So, we can say clearly that IND is important for the Capsella fruit shape and it mediates its effects by directly upregulating auxin biosynthesis in these pods to pilot growth towards these peaks,” explains Prof Lars Ostergaard of the John Innes Centre, an author on the study.

“That is what makes this study so exciting. Not only have we found out that IND has at least a partial role in creating the shape, but we have also found out what the gene does in the tissue that allows this shape to form,” he adds.

But why have these mysterious shapes evolved over the past 8 million years?

“Of the carbons and sugars that are produced in the pod from captured sunlight during photosynthesis about 50 per cent go into growing the seeds. So, we could imagine an evolutionary edge for Capsella due the its larger, flatter shape,” says Professor Ostergaard.

The Brassicaceae family includes a host of economically important domestic crops such as oilseed rape and it is possible that these latest findings in Capsella could find expression in commercial crops of tomorrow:

“By using this fundamental knowledge and translating it into the commercial crop we may be able to create a denser oilseed rape canopy with a bigger pod surface area so that seeds grow bigger and yields increase,” says Professor Ostergaard.

The findings support a growing number of studies in developmental biology which show that changes in regulatory DNA sequence in key controlling genes such as IND can lead to diverse expression patterns responsible for changes in organ shape both in natural evolution and in the domestication of crops.

Read the paper: Current Biology

Article source:John Innes Centre

Image credit: Andrew Davis

How fungi influence global plant colonisation

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The symbiosis of plants and fungi has a great influence on the worldwide spread of plant species. In some cases, it even acts like a filter. This has been discovered by an international team of researchers with participation from the University of Göttingen. The results appeared in the journal Nature Ecology & Evolution.

In the colonisation of islands by plant species, it isn’t just factors like island size, isolation and geological development that play an important role, but also the interactions between species. The scientists found that the symbiosis of plant and fungus – the mycorrhiza – is of particular importance. The two organisms exchange nutrients via the plant's fine root system: the fungus receives carbohydrates from the plant; the plant receives nutrients that the fungus has absorbed from the soil.

"For the first time, new data on the worldwide distribution of plant species in 1,100 island and mainland regions allows us to investigate the influence of this interaction on a global scale," says Dr Patrick Weigelt from the University of Göttingen’s Department of Biodiversity, Macroecology and Biogeography, who worked on the study. The results: mycorrhiza-plant interactions, which are naturally less frequent on islands because the two organisms rely on each other, mean that the colonisation of remote islands is hindered. The lack of this symbiotic relationship may act like a brake on the spread of the plants. This is not the case for plant species introduced by humans, as fungi and plants are often introduced together. Head of Department, Professor Holger Kreft, adds, "The proportion of plant species with mycorrhiza interactions also increases from the poles to the equator". One of the most prominent biogeographic patterns, the increase in the number of species from the poles to the tropics, is closely related to this symbiosis.

Dr Camille Delavaux, lead author from the University of Kansas (US), explains, “We show that the plant symbiotic association with mycorrhizal fungi is an overlooked driver of global plant biogeographic patterns. This has important consequences for our understanding of contemporary island biogeography and human-mediated plant invasions.” The results show that complex relationships between different organisms are crucial for understanding global diversity patterns and preserving biological diversity. "The absence of an interaction partner can disrupt ecosystems and make them more susceptible to biological invasions," Weigelt stresses.

Read the paper: Nature Ecology & Evolution

Article source:Georg-August-Universität Göttingen

Image credit: Holger Kreft

Scientists discover that some plants are capable of ‘rubbing’ themselves in order to achieve self fertilization

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A research team led by the University of Granada (UGR) has described a novel reproductive mechanism which actively promotes self‑pollination in certain plant species. They have called this mechanism ‘anther rubbing’.

Their study, published in the renowned journal The American Naturalist, represents the discovery of a previously unknown, unique phenomenon in the field of botany.

The mechanism consists of coordinated movements, repeated for hours, of the anthers (the end of the stamen, the part of the flower in which pollen is produced) over the stigma (the flower’s female reproductive system).

“Most plants have developed mechanisms to prevent self‑fertilization and the detrimental effects of inbreeding. However, some plants have specialized in selfing (also called ‘autogamy’), that is to say, fertilizing themselves without the need of crossing whit another plant,” explains Mohamed Abdelaziz Mohamed, professor from the UGR Department of Genetics and main author of this study.

Plants using selfing mechanisms are derived from the ones that use cross‑fertilization. Therefore, mechanisms favoring autogamy should be frequently found in nature, but such frequency has not been found. Most of the few selfing mechanisms found are passive.

“Plant movement is generally not obvious and tends to go unnoticed. Few cases present repeated and coordinated movements,” Francisco Perfectti and Mohammed Bakkali, two of the authors of this study and professors from the UGR Department of Genetics, explain.

The research, which counts with the participation of José María Gómez (CSIC) and Enrica Olivieri (UGR student), shows that anther rubbing causes self‑pollen deposition on stigmas and is sufficient to achieve maximal reproductive output, with values similar to those achieved by artificial pollination or outcrossing fertilization.

The present discovery opens a new way to understand plant reproduction and, therefore, plant evolution.

Read the paper: The American Naturalist

Article source: University of Granada

Image credit: Victor M. Vicente Selvas

Nitrogen-fixing trees “eat” rocks, play pivotal role in forest health

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By tapping nutrients from bedrock, red alder trees play a key role in healthy forest ecosystems, according to a new study.

The study published in the journal Proceedings of the National Academy of Sciences.

Researchers from Oregon State University and the U.S. Geological Survey determined red alder, through its symbiotic relationship with nitrogen-fixing bacteria, taps nutrients that are locked in bedrock, such as calcium and phosphorus. This process accelerates rock dissolution, releasing more mineral nutrients that allow plants and trees to grow.

The study addresses the long-term implications of how nutrients make their way into ecosystems, which sustain their long-term growth and productivity and ultimately store carbon, said Julie Pett-Ridge, a geochemist in OSU’s College of Agricultural Sciences and a co-author on the study.

The research also furthers the understanding of a specific set of trees that are known for their ability to naturally fertilize forests by converting atmospheric nitrogen into forms available for other plants. This process, called nitrogen fixation, is essential for natural ecosystems.

“Nitrogen mostly comes from the atmosphere, but more than 20 other nutrients mostly come from rock,” Pett-Ridge said. “We’ve established a connection between those two processes. Nitrogen-fixing trees, which we knew were special for how they bring in nitrogen from the atmosphere, also have a unique ability to accelerate the supply of rock-derived nutrients.”

Red alder is a deciduous broadleaf tree native to western North America. It is closely related to other species of alder around the world. Like all alder species, red alder can release nitrogen into soil through nodules on its roots.

In a way, red alder “eats” rocks, said Steven Perakis, an ecologist with the USGS and lead author on the National Science Foundation-funded study.

“These trees not only can add nitrogen to ecosystems, they also can add all the other nutrients that forests require to grow and store carbon,” Perakis said. “That knowledge can contribute to the sustainability of forest practices in managed forests. Farmers figured out a long time ago that nutrients were essential for maintaining productivity. These processes take a little bit longer to show themselves in forests.”

Nitrogen is the most important nutrient for plant life. But atmospheric nitrogen is useless unless its chemical bond is broken down by bacteria. Some tree species such as red alder have formed a symbiotic relationship with nitrogen-fixing bacteria. The bacteria have an enzyme that converts atmospheric nitrogen into ammonia, which promotes plant growth.

In the study, Pett-Ridge and Perakis looked at six different species of trees growing in the Tillamook State Forest in the Oregon Coast Range: Sitka spruce, Douglas-fir, western hemlock, western redcedar, bigleaf maple and red alder.

They collected leaves to analyze their strontium isotope composition, which reveals tree nutrient sources. They determined that the red alder leaves showed a stronger fingerprint of rock-derived nutrients than the other trees.

The isotope analyses were made in the W. M. Keck Collaboratory for Plasma Spectrometry at OSU. Pett-Ridge is an adjunct professor in OSU’s College of Earth, Ocean, and Atmospheric Science. Perakis is a research ecologist with the USGS Forest and Rangeland Science Center in Corvallis and a courtesy faculty member in OSU’s College of Forestry.

Read the paper: PNAS

Article source:Oregon State University

Image credit: Steven Perakis, U.S. Geological Survey

Plants’ drought alert system has unlikely evolutionary origin: underwater algae

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Plants’ water-to-land leap marks one of the most important milestones in the evolution of life on Earth. But how plants managed this transition when faced with unfamiliar challenges such as drought and bright light has been unclear.

Now, a new study shows that the built-in alert system that enables land plants to sense and respond to drought has an unlikely origin: their aquatic algal ancestors.

Researchers found that the signaling pathway that triggers plants’ drought defenses has remained virtually unchanged for hundreds of millions of years, first appearing in freshwater-dwelling streptophyte algae and later co-opted by land plants to tackle the stress of their new terrestrial environment. Today, the same pathway exists across the vast majority of the plant tree of life, from mosses, liverworts and ferns to crops and other flowering plants.

“The evolution of this pathway is one of the key events in the history of life on Earth,” said Douglas Soltis, the study’s co-corresponding author, a Florida Museum of Natural History curator and distinguished professor in the University of Florida department of biology. “Even though these algae lived underwater, they hit on some of the features that would ultimately allow plants to deal with the stress of desiccation on land. We wouldn’t be here if they hadn’t figured that out.”

Understanding the molecular details of how plants evolved this pathway is crucial as we head into a future projected to have longer and more severe droughts that could threaten our food supply, Soltis said.

“Maintaining or increasing crop yields under drought conditions, which will be exacerbated by climate change, is one of the keys to the future of agriculture,” he said. “It’s not an easy problem to solve, but it’s a big one for human health and well-being. Now that we have a blueprint for the pathway that controls plants’ drought tolerance, we may be able to manipulate it.”

Because plants can’t flee drought, they deploy an array of survival strategies while awaiting better growing conditions. Their short-term drought defense is to close their stomata – small holes that “exhale” water – and to seal moisture inside leaves with a layer of wax. During longer droughts, plants channel water and nutrients away from leaves and stems to seeds and buds, reservoirs for new growth.

One of the alert systems that coordinates plants’ detection and response to drought is known as the chloroplast retrograde signaling network. When one part of a plant senses drought or excess light, this network dispatches enzymes to carry a message to the plant’s “mainframe,” which can activate a defense strategy.

Co-corresponding authors Zhong-hua Chen of Western Sydney University and Barry Pogson of the Australian National University were studying chloroplast retrograde signaling in land plants’ stomata when Chen sent Soltis a data set that showed whether certain enzymes were absent, present and at what levels in a variety of green plant lineages. Chen included several species of algae as outgroups, organisms outside a target study group that can act as comparatives.

When Soltis downloaded the data set, it was late at night, and he was tired. But as he scanned the data, his eyes suddenly locked on the levels of two groups of enzymes in streptophyte algae, the ancestors of land plants. Why would drought-related enzymes show up in aquatic algae?

“I made sure I had the lines straight and said, ‘Whoa, this is pretty cool,’” Soltis said. “I wrote Zhong-hua back right away and said, ‘I think you’ve got something big here.’”

Streptophyte algae are freshwater plants that can survive in tough environments, including volcanic crater lakes, marine habitats and ephemeral or temporary bodies of water. Known for pioneering their way into new places, they’re also members of the lineage that gave rise to land plants. Unlike most other algae, they have protective structures around their egg and sperm cells, which Soltis cited as an example of the algae evolving features to defend themselves from stress.

While streptophyte algae don’t often face the threat of drought, Soltis said that the harsh growing conditions in some of their habitats have many of the same effects.

“High salinity is basically desiccation,” he said. “These algae may have developed some of these signal pathways because they were living in these ephemeral, salty habitats and, in the process, stumbled upon something that could be co-opted for life on land.”

Chen ’s initial hypothesis was that this drought signaling pathway had first evolved in early land plants, making it at least 450 million years old. Finding it in streptophyte algae, however, indicates that it long predates plants’ transition to land and the development of stomata.

“If this signaling pathway originated in streptophyte algae, it could potentially push the evolution of this pathway back to 580 million years ago,” said Chen, an associate professor of plant physiology and cell biology. “Of course, we will need more research to validate that.”

The research team’s analysis of the genes and proteins associated with this signaling pathway shows that they have been remarkably conserved in a variety of plant lineages. While the pathway has been studied in model plant species and crops, Soltis said streptophyte algae had simply been overlooked.

“We know so much about flowering plants, but these algae are poorly understood,” he said. “This is a great example of the value in taking a step back and seeing the bigger evolutionary picture. It gives us a deeper perspective of how this puzzle was put together to begin with.”

Given the multistep, sophisticated nature of the pathway, Chen said it would be a mistake to think of the early ancestors of land plants as primitive.

“We clearly showed that two species of streptophyte algae have evolved as many important genetic features as so-called ‘higher’ plants,” he said. “They enabled the move from an aquatic environment to land.”

Read the paper: PNAS

Article source:Florida Museum of Natural History

Image credit: CCO Public domain

With nanotubes, genetic engineering in plants is easy-peasy

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Inserting or tweaking genes in plants is more art than science, but a new technique developed by University of California, Berkeley, scientists could make genetically engineering any type of plant—in particular, gene editing with CRISPR-Cas9—simple and quick.

To deliver a gene, the researchers graft it onto a carbon nanotube, which is tiny enough to slip easily through a plant’s tough cell wall. To date, most genetic engineering of plants is done by firing genes into the tissue—a process known as biolistics—or delivering genes via bacteria. Both are successful only a small percentage of the time, which is a major limitation for scientists seeking to create disease- or drought-resistant crops or to engineer plants so they’re more easily converted to biofuels.

Nanotubes, however, are highly successful at delivering a gene into the nucleus and also into the chloroplast, a structure in the cell that is even harder to target using current methods. Chloroplasts, which have their own separate, though small, genome, absorb light and store its energy for future use, releasing oxygen in the process. An easy gene-delivery technique would be a boon for scientists now trying to improve the efficiency of light energy capture to boost crop yields.

The nanotube not only protects the DNA from being degraded by the cell, but also prevents it from being inserted into the plant's genome. As a result, the technique allows gene modifications or deletions that in the United States and countries other than the European Union would not trigger the designation "genetically modified," or GMO.

"One of the advantages is just the time saved with a technology like this," said Markita Landry, a UC Berkeley assistant professor of chemical and biomolecular engineering. "But I think the major advances are going to be the ability to quickly and efficiently deliver genes to plants across species and in a way that could enable the generation of transgenic plant lines without integration of foreign DNA into the plant genome."

A key use would be CRISPR-Cas9 gene editing: delivering the gene for Cas9, which is the enzyme that targets and cuts DNA, along with the DNA encoding guide RNA–Cas9's address label–to edit specific genes with high precision. And DNA bound to a nanotube is very hardy.

"We assessed the stability of the constructs and the cost and, on both counts, this is amenable for garage science," Landry said. "You can put these things in an envelope and mail them just about anywhere. You don't need a fridge, a gene gun, bacteria; you don't need very much to work with them, and they are stable for months. We can generate them at scale, freeze them, thaw them–they are robust little things."

Landry and her colleagues report their results in the journal Nature Nanotechnology.

CRISPR delivery

Landry discovered that nanotubes easily slip though plant cell walls, which are known for their tough layers, while trying to label cells with nanotube sensors. The sensors ended up inside the cell, not on the cell surface.

She immediately saw how to flip this around to deliver genes into plants. Current methods are cumbersome and can be low-yield. Using gene guns is destructive; it's like blowing a hole in a plant cell and hoping your gene and the cell both survive. Not all plants can be infected by gene-carrying Agrobacterium, and another technique, using pathogenic viruses to carry genes, works for an even narrower range of plants and risks inserting viral DNA into the plant's genome. All have to be customized for each plant, and the DNA delivered is integrated into the genome: the definition of GMO.

Eager to give it a try, Landry and her colleagues wrapped the gene for green fluorescent protein (GFP) around a nanotube and injected it into an organic arugula leaf purchased from a local Whole Foods Market. Within a day, the plant cells glowed green under UV light, indicating that the GFP gene had been transcribed and translated into protein, as if it were the plant's own gene.

The effect lasted only a few days, however, probably because the proteins get recycled, and the DNA slowly degrades.

A short lifetime is not a drawback, however.

"Part of what makes the platform unique is that the expression is transient. When we look in the microscope seven to 10 days later, the expression is gone, the fluorescence is gone. That is not the case with Agrobacterium," Landry said. For scientists studying how plants work, expressing a gene for a short time can tell them a lot about the gene's role in the cell.

"For this to be a widely useful platform, however, we need to express a protein that in and of itself has a permanent effect on the nuclear genome," she added.

Her plan is to package DNA into a single-stranded plasmid that is then attached to a carbon nanotube. Within two or three days after diffusing into the cell, both the Cas9 protein and CRISPR guide RNA would be expressed, allowing them to link up to form a ribonucleoprotein complex that edits the genome, permanently. She has not found any toxic effects from the nanotube.

"So, now you have a plant that is edited, but that would be considered non-GMO outside of Europe," she said.

Charging up the nanotube

She and her colleagues tested nanotube delivery in other plants: tobacco, a workhorse of plant genetics; cotton, whose genome is notoriously hard to crack; and wheat. Genetically engineered versions of these plants are already on the market, but a simplified technique could speed the introduction of new and beneficial genes. Tobacco, for example, has been engineered to produce pharmaceuticals such as anticancer drugs.

Though Landry and her colleagues do not yet fully understand how nanotube delivery works, the easy entry of nanotubes is not a total surprise, she said. The cell walls of plants let things slip in easily if they are smaller than about 5 to 20 nanometers, which is much less than the 500 nanometer-size limit of mammalian cells. The nanotubes are about 1 nanometer in diameter, though they're some 300 nanometers long: enough room to attach dozens of genes. Plant cells are on the order of 10,000 nanometers across.

She and her lab colleagues tried various techniques for attaching DNA to nanotubes and found that the tightest binding worked best. When the researchers gave the nanotube a positive charge before introducing the DNA, it stuck like paper to a comb charged with static electricity.

She is now conducting experiments with DNA origami nanoparticles to better understand what is happening inside the plant cells after the nanotube and DNA enter, and is experimenting with nanotube delivery into plants of other types of molecules, specifically RNA and proteins.

"The amazing thing about these carbon nanotubes is that they're able to get past the cell wall and go into the nucleus or into the chloroplasts. It's a novel advance that's allowing us to really put in place the tools for genome editing," said Brian Staskawicz, a professor of plant and microbial biology and the scientific director for agriculture of the Innovative Genomics Institute, which is funding further work on CRISPR delivery by Landry and her team. "The next steps would be, can we deliver ribonucleic proteins or can we deliver mRNA or DNA that would actually encode CRISPR-Cas9?"

Read the paper: Nature Nanotechnology

Article source:UC Berkeley

Image credit: Ella Marushchenko

New pathway that may help develop more resilient crop varieties

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Researchers from the Department of Plant Sciences, University of Oxford, have discovered a new biochemical pathway in plants which they have named CHLORAD.

By manipulating the CHLORAD pathway, scientists can modify how plants respond to their environment. For example, the plant’s ability to tolerate stresses such as high salinity can be improved.

The researchers hope that their results, published in Science, will open the way to new crop improvement strategies, which will be vital as we face the prospect of delivering food security for a population that is projected to reach nearly 10 billion by 2050.

The CHLORAD pathway helps to regulate structures inside plant cells called chloroplasts. Chloroplasts are the organelles that define plants. Along with many other metabolic, developmental and signalling functions, chloroplasts are responsible for photosynthesis – the process whereby sunlight energy is harnessed to power the cellular activities of life.

Consequently, chloroplasts are essential, not only for plants but also for the myriad ecosystems that depend on plants, and for agriculture.

Chloroplasts are composed of thousands of different proteins, most of which are made elsewhere in the cell and imported by the organelle. These proteins must all be very carefully regulated to ensure that the organelle keeps functioning properly. The CHLORAD pathway works by removing and disposing of unnecessary or damaged chloroplast proteins; hence the name CHLORAD, which stands for “chloroplast-associated protein degradation”.

Professor Paul Jarvis, lead researcher, said: ‘Two decades on from the identification of the chloroplast protein import machinery – which delivers new proteins to chloroplasts – our discovery of the CHLORAD pathway reveals for the first time how individual, unwanted proteins are removed from chloroplasts.’

Researcher, Dr Qihua Ling, said: ‘Our previous studies showed that proteins in the chloroplast membranes are digested by a protein degradation system outside of chloroplasts. So, the key question was: How are chloroplast proteins extracted from the membrane to enable this to happen? Our discovery of the CHLORAD system answers this question, and we identified two novel proteins that act in the process.’

Co-researcher, Dr William Broad, added: ‘Chloroplasts are eukaryotic organelles that originated more than a billion years ago from photosynthetic bacteria, by a process called endosymbiosis. Remarkably, the CHLORAD system contains a mix of components of eukaryotic origin and bacterial origin. This provides a fascinating example of how eukaryotic host cells have evolved gradually, co-opting available tools in novel ways, to govern their endosymbiotic organelles.’

Peter Burlinson, Frontier Bioscience Lead at the Biotechnology and Biological Sciences Research Council, said: ‘The discovery of this biochemical pathway is a good example of how insights from fundamental plant biology research can reveal potential new strategies to develop crops that are more productive and resilient. This helps illustrate the value of basic science in contributing to addressing key global challenges including a rising global population, environmental stresses and an increased demand to deliver food security.’

By the year 2050, the current level of food production must increase by at least 70% to meet the demands of a growing world population and shifting dietary preferences towards more animal products, while 38% of the world’s land and 70% of fresh water are already used for agriculture. Abiotic stresses, including drought, high and low temperatures, soil salinity, nutrient deficiencies, and toxic metals, are the leading cause of yield loss, decreasing crop productivity by 50–80% depending on the crop and geographical location.

Thus, developing stress-resistant crops that can have stable yields under stress conditions is an important strategy to ensure future food security. This need is particularly urgent considering the increased frequency of extreme weather conditions that accompany global climate change, which cause more severe environmental stresses, more frequent plant disease outbreaks, and reduced yield and harvest quality.

Read the paper: Science

Article source:University of Oxford

Image credit: CCO Public domain

How plants learned to save water

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Plants that can manage with less water could make agriculture more sustainable. This is why a research team at the University of Würzburg is investigating how plants control their water balance.

Tiny pores on the leaves of plants, called stomata, have a huge influence on the state of our planet. Through the stomata, plants absorb carbon dioxide, which is incorporated into carbohydrates, and release oxygen. But they also lose water through open pores, which can be life-threatening for plants in dry conditions.

Plants therefore have developed complex signalling pathways that optimize the opening width of stomata to match the environmental conditions. In response to changes in the availability of light, carbon dioxide and water, they can open or close these pores. How did the signalling pathways that are responsible for this regulation evolve? This is being investigated at Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, in the team of the plant scientist Rainer Hedrich.

"We are currently collecting and analyzing data from different plant species," says Professor Hedrich. He explains that this research also has relevance for agriculture: "Knowledge about the evolution of these signalling pathways could feed into breeding efforts to develop crops that can grow with less water.” After all, the majority of the drinking water supplied to plants via irrigation systems is lost through stomatal pores. In view of climate change, plant varieties that can cope well with drought are highly sought-after.

History of important genes reconstructed

In the journal Trends in Plant Science, JMU researchers Dr. Frances Sussmilch, Professor Jörg Schultz, Professor Hedrich, and Dr. Rob Roelfsema now summarize the current state of knowledge on the signalling pathways that plants use to regulate their water balance.

The Würzburg team has reconstructed the evolutionary history of important genes that control the movement of leaf pores in flowering plants. It turned out that most of these genes belong to old gene families that occur in all plant groups, including green algae. These gene families probably developed before the first plants colonized the land.

The researchers also found out that some specific genes that control the opening and closing of leaf pores in response to light and carbon dioxide probably only developed in seed plants or flowering plants after they had been separated in evolution from a common ancestor with ferns.

Specific signalling genes in adjustable guard cells

In their work, the JMU scientists look closely at the plants’ guard cells. These two cells surround each leaf pore. When hydraulic pressure rises in the guard cells, the pores open. If the pressure decreases, the pore closes.

In the guard cells of flowering plants, the products of certain key signalling genes have unique properties or are found in much higher concentrations than in the surrounding leaf cells. The specificity of these genes is likely important for controlling the hydraulic pressure in the guard cells.

The researchers have also examined related genes using available data for the moss Physcomitrella patens. "We found out that none of the moss genes of interest were specific for stomatal-bearing tissue, but instead all these genes were also expressed in tissues without these pores," said Frances Sussmilch. Rob Roelfsema and Jörg Schultz add: "Signalling genes with specific roles in guard cells probably arose later in plant evolution after the divergence of mosses from an ancestor they share with flowering plants.”

Read the paper: Nature Ecology and Evolution

Article source:Julius-Maximilians-Universität Würzburg (JMU)

Image credit: Stephan Liebig

Complete world map of tree diversity: New statistical model eliminates blank spaces

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The biodiversity of our planet is one of our most precious resources. However, for most places in the world, we only have a tiny picture of what this diversity actually is. Researchers at the German Centre for Integrative Biodiversity Research (iDiv) and Martin Luther University Halle-Wittenberg (MLU) have now succeeded in constructing, from scattered data, a world map of biodiversity showing numbers of tree species. With the new map, the researchers were able to infer what drives the global distribution of tree species richness. Climate plays a central role; however, the number of species that can be found in a specific region also depends on the spatial scale of the observation, the researchers report in the journal Nature Ecology and Evolution. The new approach could help to improve global conservation.

Around the world, biodiversity is changing dramatically and its protection has become one of the greatest challenges mankind is facing. At the same time, we still know very little about why some places are biologically diverse while others are poor, and where are the most biodiverse places on Earth. Also, the reasons why some areas are more species-rich than others are often unclear: what role do environmental factors like climate play, and how important are historical factors like past ice ages for the biodiversity we are observing today? Our knowledge is based on scattered local surveys and is full of gaps; especially in tropical regions, where biodiversity can be particularly high. Closing all gaps by comprehensively surveying the whole planet, is, however, simply impossible.

Satellite imagery can close some data gaps; for example, when collating information on forest cover, but these techniques have their limits. “We don’t have to just count the trees, we also need to identify what species they are,” explains Dr Petr Keil, lead author of the new study. “In the tropics, we find hundreds of different tree species in a single hectare. We can identify these only on site. Therefore, most areas haven’t been surveyed for biological diversity – and probably never will be.” Keil and co-author Prof Jonathan Chase are scientists at the German Centre for Integrative Biodiversity Research (iDiv) and at the Martin Luther University Halle-Wittenberg (MLU).

Despite the patchy data, Keil and Chase wanted to create a world map of tree species richness. In a first step, they compiled well over 1,000 lists of tree species. These came either from small forest plots which had been surveyed in previous studies, or from whole countries. For most countries in the world, it is known which tree species can be found there, but not where exactly, and also it is often unclear whether specific species are rare or common. In order to be able to calculate the number of tree species for the extensive blank spaces on the map, the researchers developed a statistical model. The trick is that the model combines the available patchy information on the surveyed plots with the information on the country level and also integrates established data on environmental factors like climate. The result is a complete map of biodiversity in all the forested areas in the world.

“It was like a 1000-piece puzzle that we only had a few pieces of, and we didn’t even know what the big picture was,” says Jonathan Chase. “With our approach, we were able to calculate the missing pieces and put the puzzle together.” Using the new method, the researchers can calculate the number of tree species for areas of different sizes; a nature reserve, a country or an entire continent. This enabled them to investigate the underlying causes of the variation of tree diversity on our planet. Their analysis revealed that climate is the most important factor; the highest number of tree species can be found in the hot, humid tropics. Nevertheless, the number of tree species also varies across different places with the same climate, in some cases quite substantially. In southern China, for example, the researchers see a much higher diversity than in other regions with a similar climate.

Importantly, however, just how much ‘extra’ diversity one finds in places like China depends on the view of the observer. “If you’re standing in a forest counting the number of species around you, you might not even notice the difference between China and other climatically similar areas. However, when you move from one site to the next and add up species observed across many sites, the difference really pops out”, Jonathan Chase says.

This disparity between adjacent areas is called beta diversity. Within a larger region it leads to a high total diversity. Keil and Chase have shown in their analysis that this measure of diversity is particularly high in the dry (not wet) tropics, especially in mountainous areas like in southern China, Mexico, or in the Ethiopian highlands. One reason for this high beta-diversity might be events in the geological past, like ice ages. “During the last glaciation, the trees could survive only in mountain valleys, and different populations were isolated from each other as a result,” explains Petr Keil . “If you stand in one of these valleys today, you see a medium number of tree species. But if you climb over the ridge and hike down into the neighbouring valley, you find different tree species, and still others in the next valley.”

Keil and Chase are primarily concerned with understanding how biodiversity is distributed on the planet and what factors are driving it. But their model can also be useful for developing strategies for conservation, especially in forests where tree diversity has not been heavily influenced by humans. For example, in the case of the mountains of China, protecting only one valley is not enough; it is the diversity of different valleys which gives this area its high biological value. “In order to really understand and protect biodiversity, we have to look at the local and regional scale at the same time,” says Keil. “That is, we need both the perspective of a naturalist standing in a forest and the big picture of an entire country. Our approach now enables that”.

Read the paper: Nature Ecology and Evolution

Article source:German Centre for Integrative Biodiversity Research (iDiv)

Image credit: Petr Keil and Jonathan Chase