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Plant Science

stomata

How Plants Measure Their CO2 Uptake

By | News, Plant Science, Research

Plants face a dilemma in dry conditions: they have to seal themselves off to prevent losing too much water but this also limits their uptake of carbon dioxide. A sensory network assures that the plant strikes the right balance.

When water is scarce, plants can close their pores to prevent losing too much water. This allows them to survive even longer periods of drought, but with the majority of pores closed, carbon dioxide uptake is also limited, which impairs photosynthetic performance and thus plant growth and yield.

Plant accomplish a balancing act – navigating between drying out and starving in dry conditions – through an elaborate network of sensors. An international team of plant scientists led by Rainer Hedrich, a biophysicist from Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, has now pinpointed these sensors. The results have been published in the journal Nature Plants.

Microvalves control photosynthesis and water supply

When light is abundant, plants open the pores in their leaves to take in carbon dioxide (CO2) which they subsequently convert to carbohydrates in a process called photosynthesis. At the same time, a hundred times more water escapes through the microvalves than carbon dioxide flows in.

This is not a problem when there is enough water available, but when soils are parched in the middle of summer, the plant needs to switch to eco-mode to save water. Then plants will only open their pores to perform photosynthesis for as long as necessary to barely survive. Opening and closing the pores is accomplished through specialised guard cells that surround each pore in pairs. The units comprised of pores and guard cells are called stomata.

Guard cells have sensors for CO2 and ABA

The guard cells must be able to measure the photosynthesis and the water supply to respond appropriately to changing environmental conditions. For this purpose, they have a receptor to measure the CO2 concentration inside the leaf. When the CO2 value rises sharply, this is a sign that the photosynthesis is not running ideally. Then the pores are closed to prevent unnecessary evaporation. Once the CO2 concentration has fallen again, the pores reopen.

The water supply is measured through a hormone. When water is scarce, plants produce abscisic acid (ABA), a key stress hormone, and set their CO2 control cycle to water saving mode. This is accomplished through guard cells which are fitted with ABA receptors. When the hormone concentration in the leaf increases, the pores close.

Analysing the CO2-ABA network

The JMU research team wanted to shed light on the components of the guard cell control cycles. For this purpose, they exposed Arabidopsis species to elevated levels of CO2 or ABA. They did so over several hours to trigger reactions at the level of the genes. Afterwards, the stomata were isolated from the leaves to analyse the respective gene expression profiles of the guard cells using bioinformatics techniques. For this task, the team took Tobias Müller and Marcus Dietrich on board, two bioinformatics experts at the University of Würzburg.

The two experts found out that the gene expression patterns differed significantly at high CO2 or ABA concentrations. Moreover, they noticed that excessive CO2 also caused the expression of some ABA genes to change. These findings led the researchers to take a closer look at the ABA signalling pathway. They were particularly interested in the ABA receptors of the PYR/PYL family (pyrabactin receptor and pyrabactin-like). Arabidopsis has 14 of these receptors, six of them in the guard cells.

ABA receptors under the microscope

“Why does a guard cell need as many as six receptors for a single hormone? To answer this question, we teamed up with Professor Pedro Luis Rodriguez from the University of Madrid, who is an expert in ABA receptors,” says Hedrich. Rodriguez’s team generated Arabidopsis mutants in which they could study the ABA receptors individually.

“This enabled us to assign each of the six ABA receptors a task in the network and identify the individual receptors which are responsible for the ABA- and CO2-induced closing of the stomata,” Peter Ache, a colleague of Hedrich‘s, explains.

Guard cells use ABA as currency in calculations

“We conclude from the findings that the guard cells offset the current photosynthetic carbon fixation performance with the status of the water balance using ABA as the currency,” Hedrich explains. “When the water supply is good, our results indicate that the ABA receptors evaluate the basic hormonal balance as quasi ‘stress-free’ and keep the stomata open for CO2 supply. When water is scarce, the drought stress receptors recognise the elevated ABA level and make the guard cells close the stomata to prevent the plant from drying out.”

Next, the JMU researchers aim to study the special characteristics of the ABA and CO2 relevant receptors as well as their signalling pathways and components.

Read the paper: Nature Plants

Article source: UNIVERSITY OF WÜRZBURG

Image:  Rainer Hedrich & Peter Ache / Universität Würzburg

roots

Gene identified that will help develop plants to fight climate change

By | Climate change, News, Plant Science

Hidden underground networks of plant roots snake through the earth foraging for nutrients and water, similar to a worm searching for food. Yet, the genetic and molecular mechanisms that govern which parts of the soil roots explore remain largely unknown. Now, Salk Institute researchers have discovered a gene that determines whether roots grow deep or shallow in the soil.

In addition, the findings, published in Cell, will also allow researchers to develop plants that can help combat climate change as part of Salk’s Harnessing Plants Initiative. The initiative aims to grow plants with more robust and deeper roots that can store increased amounts of carbon underground for longer to reduce CO2 in the atmosphere. The Salk initiative will receive more than $35 million from over 10 individuals and organizations through The Audacious Project to further this effort.

“We are incredibly excited about this first discovery on the road to realizing the goals of the Harnessing Plants Initiative,” says Associate Professor Wolfgang Busch, senior author on the paper and a member of Salk’s Plant Molecular and Cellular Biology Laboratory as well as its Integrative Biology Laboratory. “Reducing atmospheric CO2 levels is one of the great challenges of our time, and it is personally very meaningful to me to be working toward a solution.”

In the new work, the researchers used the model plant thale cress (Arabidopsis thaliana) to identify genes and their variants that regulate the way auxin, a hormone that is a key factor in controlling the root system architecture, works. Though auxin was known to influence almost all aspects of plant growth, it was not known which factors determined how it specifically affects root system architecture.

“In order to better view the root growth, I developed and optimized a novel method for studying plant root systems in soil,” says first author Takehiko Ogura, a postdoctoral fellow in the Busch lab. “The roots of A. thaliana are incredibly small so they are not easily visible, but by slicing the plant in half we could better observe and measure the root distributions in the soil.”

The team found that one gene, called EXOCYST70A3, directly regulates root system architecture by controlling the auxin pathway without disrupting other pathways. EXOCYST70A3 does this by affecting the distribution of PIN4, a protein known to influence auxin transport. When the researchers altered the EXOCYST70A3 gene, they found that the orientation of the root system shifted and more roots grew deeper into the soil.

“Biological systems are incredibly complex, so it can be difficult to connect plants’ molecular mechanisms to an environmental response,” says Ogura. “By linking how this gene influences root behavior, we have revealed an important step in how plants adapt to changing environments through the auxin pathway.”

In addition to enabling the team to develop plants that can grow deeper root systems to ultimately store more carbon, this discovery could help scientists understand how plants address seasonal variance in rainfall and how to help plants adapt to changing climates.

“We hope to use this knowledge of the auxin pathway as a way to uncover more components that are related to these genes and their effect on root system architecture,” adds Busch. “This will help us create better, more adaptable crop plants, such as soybean and corn, that farmers can grow to produce more food for a growing world population.”

Other authors included Santosh B. Satbhai of Salk along with Christian Goeschl, Daniele Filiault, Madalina Mirea, Radka Slovak and Bonnie Wolhrab of the Gregor Mendel Institute in Austria.

About the Harnessing Plants Initiative:

Climate change poses an immediate threat to our future. Rising temperatures from excess carbon dioxide in the atmosphere has led to increasingly extreme and dangerous weather patterns that threaten animals and plants alike. The Salk Institute’s Harnessing Plants Initiative (HPI) is an innovative, scalable and bold approach to fight climate change by optimizing a plant’s natural ability to capture and store carbon and adapt to diverse climate conditions. This approach can help draw down and store more carbon and that—combined with other global efforts—will mitigate the disastrous effects of climate change while providing more food, fuel and fiber for a growing population.

Read the paper: Cell

Article source: Salk Institute

Image: Salk Institute

Genetic breakthrough in cereal crops could help improve yields worldwide

By | Agriculture, News, Plant Science

A team of Clemson University scientists has achieved a breakthrough in the genetics of senescence in cereal crops with the potential to dramatically impact the future of food security in the era of climate change.

The collaborative research, which explores the genetic architecture of the little understood process of senescence in maize (a.k.a. corn) and other cereal crops, was published in The Plant Cell, one of the top peer-reviewed scientific journals of plant sciences. Rajan Sekhon, a plant geneticist and an assistant professor in the College of Science’s department of genetics and biochemistry, is the lead and corresponding author of the paper titled “Integrated Genome-Scale Analysis Identifies Novel Genes and Networks Underlying Senescence in Maize.”

“Senescence means ‘death of a cell or an organ in the hands of the very organisms it is a part of,’ ” Sekhon said. “It happens pretty much everywhere, even in animals. We kill the cells we don’t need. When the weather changes in fall, we have those nice fall colors in trees. At the onset of fall, when the plants realize that they cannot sustain the leaves, they kill their leaves. It is all about the economy of energy.”

As a result, the leaves die off after their show of color. The energy scavenged from the leaves is stored in the trunk or roots of the plant and used to quickly reproduce leaves next spring. This makes perfect sense for trees. But the story is quite different for some other edible plants, specifically cereal crops like maize, rice and wheat.

“These crops are tended very carefully and supplied excess nutrients in the form of fertilizers by the farmers,” Sekhon said. “Instead of dying prematurely, the leaves can keep on making food via photosynthesis. Understanding the triggers for senescence in crops like maize means scientists can alter the plant in a way that can benefit a hungry world.”

Sekhon, whose research career spans molecular genetics, genomics, epigenetics and plant breeding, established his lab in 2014 as an assistant professor. He has played a key role in the development of a “gene atlas” widely used by the maize research community. He has published several papers in top peer-reviewed journals investigating the regulation of complex plant traits.

“If we can slow senescence down, this can allow the plant to stay green – or not senesce – for a longer period of time,” Sekhon said. “Plant breeders have been selecting for plants that senesce late without fully understanding how senescence works at the molecular level.”

These plants, called “stay-green,” live up to their name. They stay green longer, produce greater yields and are more resilient in the face of environmental factors that stress plants, including drought and heat.

But even with the existence of stay-green plants, there has been little understanding about the molecular, physiological and biochemical underpinnings of senescence. Senescence is a complex trait affected by several internal and external factors and regulated by a number of genes working together. Therefore, off-the-shelf genetic approaches are not effective in fully unraveling this enigmatic process. The breakthrough by Sekhon and his colleagues was the result of a systems genetics approach.

Sekhon and the other researchers studied natural genetic variation for the stay-green trait in maize. The process involved growing 400 different maize types, each genetically distinct from each other based on the DNA fingerprint (i.e., genotype), and then measuring their senescence (i.e., phenotype). The team then associated the “genotype” of each inbred line with its “phenotype” to identify 64 candidate genes that could be orchestrating senescence.

“The other part of the experiment was to take a stay-green plant and a non-stay-green plant and look at the expression of about 40,000 genes during senescence,” Sekhon said. “Our researchers looked at samples every few days and asked which genes were gaining expression during the particular time period. This identified over 600 genes that appear to determine whether a plant will be stay-green or not.

“One of the big issues with each of these approaches is the occurrence of false positives, which means some of the detected genes are flukes, and instances of false negatives, which means that we miss out on some of the causal genes.”

Therefore, Sekhon and his colleagues had to painstakingly combine the results from the two large experiments using a “steams genetics” approach to identify some high-confidence target genes that can be further tested to confirm their role in senescence. They combined datasets to narrow the field to 14 candidate genes and, ultimately, examined two genes in detail.

“One of the most remarkable discoveries was that sugars appear to dictate senescence,” Sekhon said. “When the sugars are not moved away from the leaves where these are being made via photosynthesis, these sugar molecules start sending signals to initiate senescence.”

However, not all forms of sugar found in the plants are capable of signaling. One of the genes that Sekhon and colleagues discovered in the study appears to break complex sugars in the leaf cells into smaller sugar molecules – six-carbon sugars like glucose and fructose – that are capable of relaying the senescence signals.

“This is a double whammy,” Sekhon said. “We are not only losing these extra sugars made by plants that can feed more hungry mouths. These unused sugars in the leaves start senescence and stop the sugars synthesis process all together.”

The implications are enormous for food security. The sugars made by these plants should be diverted to various plant organs that can be used for food.

“We found that the plant is carefully monitoring the filling of the seeds. That partitioning of sugar is a key factor in senescence. What we found is there is a lot of genetic variation even in the maize cultivars that are grown in the U.S.”

Some plants fill seeds and then can start filling other parts of the plant.

“At least some of the stay-green plants are able to do this by storing extra energy in the stems,” Sekhon said. “When the seed is harvested, whatever is left in the field is called stover.”

Stover can be used as animal feed or as a source of biofuels. With food and energy demand increasing, there is a growing interest in developing dual-purpose crops which provide both grain and stover. As farmland becomes scarce, plants that senesce later rise in importance because they produce more overall energy per plant.

The genes identified in this study are likely performing the same function in other cereal crops, such as rice, wheat and sorghum. Sekhon said that the next step is to examine the function of these genes using mutants and transgenics.

“The ultimate goal is to help the planet and feed the growing world. With ever-worsening climate, shrinking land and water, and increasing population, food security is the major challenge faced by mankind,” Sekhon said.

In addition to Sekhon, other contributors include Rohit Kumar, Christopher Saski, Arlyn Ackerman, William Bridges, Barry Flinn and Feng Luo of Clemson University; Timothy Beissinger of the University of Gottingen; and Matthew Breitzman, Natalia de Leon and Shawn Kaeppler of the University of Wisconsin-Madison.

Read the paper: The Plant Cell

Article source: Clemson University

Image: Clemson University/College of Science

seaweed

Scientists Discover the Biggest Seaweed Bloom in the World

By | News, Plant Science

Scientists led by the University of South Florida College of Marine Science used NASA satellite observations to discover the largest bloom of macroalgae in the world called the Great Atlantic Sargassum Belt (GASB), as reported in Science.

They confirmed that the belt of brown macroalgae called Sargassum forms its shape in response to ocean currents, based on numerical simulations. It can grow so large that it blankets the surface of the tropical Atlantic Ocean from the west coast of Africa to the Gulf of Mexico. This happened last year when more than 20 million tons of it – heavier than 200 fully loaded aircraft carriers – floated in surface waters and some of which wreaked havoc on shorelines lining the tropical Atlantic, Caribbean Sea, Gulf of Mexico, and east coast of Florida.

The team also used environmental and field data to suggest that the belt forms seasonally in response to two key nutrient inputs: one human-derived, and one natural.

In the spring and summer, Amazon River discharge adds nutrients to the ocean, and such discharged nutrients may have increased in recent years due to increased deforestation and fertilizer use. In the winter, upwelling off the West African coast delivers nutrients from deep waters to the ocean surface where the Sargassum grows.

“The evidence for nutrient enrichment is preliminary and based on limited field data and other environmental data, and we need more research to confirm this hypothesis,” said Dr. Chuanmin Hu of the USF College of Marine Science, who led the study and has studied Sargassum using satellites since 2006. “On the other hand, based on the last 20 years of data, I can say that the belt is very likely to be a new normal,” said Hu.

Hu spearheaded the work with first author Dr. Mengqiu Wang, a postdoctoral scholar in his Optical Oceanography Lab at USF. The team included others from USF, Florida Atlantic University, and Georgia Institute of Technology. The data they analyzed from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) between 2000-2018 indicates a possible regime shift in Sargassum blooms since 2011.

“The scale of these blooms is truly enormous, making global satellite imagery a good tool for detecting and tracking their dynamics through time,” said Woody Turner, manager of the Ecological Forecasting Program at NASA Headquarters in Washington.

In patchy doses in the open ocean, Sargassum contributes to ocean health by providing habitat for turtles, crabs, fish, and birds and producing oxygen via photosynthesis like other plants. “In the open ocean, Sargassum provides great ecological values, serving as a habitat and refuge for various marine animals. I often saw fish and dolphins around these floating mats,” Wang said.

But too much of this seaweed makes it hard for certain marine species to move and breathe, especially when the mats crowd the coast. When it dies and sinks to the ocean bottom at large quantities it can smother corals and seagrasses. On the beach, rotten Sargassum releases hydrogen sulfide gas and smells like rotten eggs, potentially presenting health challenges for people on beaches who have asthma, for example.

2011: A Tipping Point

Before 2011, most of the pelagic Sargassum in the ocean was primarily found floating in patches around the Gulf of Mexico and Sargasso Sea. The Sargasso Sea is located on the western edge of the central Atlantic Ocean and named after its popular algal resident. Christopher Columbus first reported Sargassum from this crystal-clear ocean in the 15th century, and many boaters of the Sargasso Sea are familiar with this seaweed.

In 2011, Sargassum populations started to explode in places it hadn’t been before, like the central Atlantic Ocean, and it arrived in gargantuan gobs that suffocated shorelines and introduced a new nuisance for local environments and economies. Some countries, such as Barbados, declared a national emergency last year because of the toll this once-healthy seaweed took on tourism.

“The ocean’s chemistry must have changed in order for the blooms to get so out of hand,” Hu said. Sargassum reproduces vegetatively, and it probably has several initiation zones around the Atlantic Ocean. It grows faster when nutrient conditions are favorable and when its internal clock ticks in favor of reproduction.

To unravel the mystery, the team analyzed fertilizer consumption patterns in Brazil, Amazon deforestation rates, Amazon River discharge, two years of nitrogen and phosphorus measurements taken from the central western parts of the Atlantic Ocean, among other ocean properties.

While the data are preliminary, the pattern seems clear: the explosion in Sargassum correlates to increases in deforestation and fertilizer use, both of which have increased since 2010.

A Recipe for a Doom and Gloom Bloom

The team identified key factors that are critical to bloom formation: a large seed population in the winter left over from a previous bloom, nutrient input from West Africa upwelling in winter, and nutrient input in the spring or summer from the Amazon River. In addition, Sargassum only grows well when salinity is normal and surface temperatures are normal or cooler.

The 2011 bloom was likely caused by Amazon River discharge in previous years, Wang said, but was driven to even larger proportions by the double whammy of upwelling in the eastern Atlantic and river discharge on the western Atlantic.

As noted in the satellite imagery, major blooms occurred in every year between 2011 and 2018 except 2013 – and the cocktail of ingredients necessary explains why. No bloom occurred in 2013 because the seed populations measured during winter of 2012 were unusually low, Wang said.

Hu also explained why the tipping point started in 2011 instead of 2010, even on the heels of significant Amazon discharge in 2009. Significant rain in 2009 introduced freshwater to the ocean, which reduced salinity. Plus, in 2010 the sea surface temperature was higher than normal. Sargassum didn’t bloom in either 2009 or 2010 because these conditions do not favor Sargassum growth.

“This is all ultimately related to climate change because it affects precipitation and ocean circulation and even human activities, but what we’ve shown is that these blooms do not occur because of increased water temperature,” Hu said. “They are probably here to stay.”

The team reports that a more detailed seasonal pattern likely to be recurring looks like this:

  • January: Sargassum in Central Atlantic provides the seeds for the subsequent spring-summer blooms
  • Jan-April: Sargassum develops into a bloom extending to the tropical Atlantic (some may reach Caribbean)
  • Apr – July: Blooms continue to develop into a Great Atlantic Sargassum Belt (extends northwestward by the North Brazil Current and North Equatorial Current, and eastward to the West Africa coast by the North Equatorial Counter Current)
  • After July: Bloom continues to the eastern Atlantic while overall abundance begins to decrease
  • Sept-Oct: Bloom gradually dissipates
  • Winter: Either the mats dissipate (as in 2012) or contribute to new blooms in the coming year

No Crystal Ball and More Work Needed

The Sargassum bloom in the Caribbean during the early parts of this year was even worse than last year, Hu said, and it’s likely to impact holiday vacations in the northern Caribbean and south Florida, including Dominican Republic, Puerto Rico, Jamaica, Quintana Roo, Florida Keys, Miami Beach, and Palm Beach.

In general, predicting future blooms is difficult, Hu said, because the blooms depend on a wide-ranging spectrum of factors that are hard to predict. There’s a lot left to understand, too, such as whether and how the Sargassum belt affects fisheries.

“We hope this provides a framework for improved understanding and response to this emerging phenomenon,” Hu said. “We need a lot more follow-on work.”

Read the paper: Science

Article source: University of South FLorida

Image: Brian Cousin, Florida Atlantic University’s Harbor Branch Oceanographic Institute

Plant nutrient detector breakthrough

By | Agriculture, News, Plant Science, Research

Findings from La Trobe University-led research could lead to less fertiliser wastage, saving millions of dollars for Australian farmers.

Published in the journal Plant Physiology, the findings provide a deeper understanding of the mechanisms whereby plants sense how much and when to take in the essential nutrient, phosphorus, for optimal growth.

Lead author Dr Ricarda Jost, from the Department of Plant, Animal and Soil Sciences at La Trobe University said the environmental and economic benefits to farmers could be significant.

“In countries like Australia where soils are phosphorus poor, farmers are using large amounts of expensive, non-renewable phosphorus fertiliser, such as superphosphate or diammonium phosphate (DAP), much of which is not being taken up effectively by crops at the right time for growth,” Dr Jost said.

“Our findings have shown that a protein called SPX4 senses the nutrient status – the ‘amount of fuel in the tank’ of a crop – and alters gene regulation to either switch off or turn on phosphorus acquisition, and to alter growth and flowering time.”

Using Arabidopsis thaliana (thale or mouse-ear cress) shoots, the research team conducted genetic testing by adding phosphorus fertiliser and observing the behaviour of the protein.

For the first time, the SPX4 protein was observed to have both a negative and a positive regulatory effect on phosphorus take-up and resulting plant growth.

“The protein senses when the plant has taken in enough phosphorus and tells the roots to stop taking it up,” Dr Jost said. “If the fuel pump is turned off too early, this can limit plant growth.

“On the other hand, SPX4 seems to have a ‘moonlighting’ activity and can activate beneficial processes of crop development such as initiation of flowering and seed production.”

This greater understanding of how SPX4 operates could lead to a more precise identification of the genes it regulates, and an opportunity to control the protein’s activity using genetic intervention – switching on the positive and switching off the negative responses.

La Trobe agronomist Dr James Hunt said the research findings sit well with the necessity for Australian farmers’ to be as efficient as possible with costly fertiliser inputs.

“In our no-till cropping systems, phosphorus gets stratified in the top layers of soil. When this layer gets dry, crops cannot access these reserves and enter what we a call a phosphorus drought,” Dr Hunt said.

“The phosphorus is there, but crops can’t access it in the dry soil. If we could manipulate crop species to take up more phosphorus when the top soil is wet, we’d be putting more fuel in the tank for later crop growth when the top soil dries out.”

The research team will now be investigating in more detail how SPX4 interacts with gene regulators around plant development and controlling flowering time.

The research was published in Plant Physiology with collaborators from Zhejiang University (China), Ghent University & VIB Center for Plant Systems Biology (Belgium), French Alternative Energies and Atomic Energy Commission (CEA) and the Australian Research Council Centre of Excellence in Plant Energy Biology.

Read the paper: Plant Physiology

Article source: La Trobe University

Image: Free-Photos / Pixabay

Researchers can finally modify plant mitochondrial DNA

By | News, Plant Science

Researchers in Japan have edited plant mitochondrial DNA for the first time, which could lead to a more secure food supply.

Nuclear DNA was first edited in the early 1970s, chloroplast DNA was first edited in 1988, and animal mitochondrial DNA was edited in 2008. However, no tool previously successfully edited plant mitochondrial DNA.

Researchers used their technique to create four new lines of rice and three new lines of rapeseed (canola).

“We knew we were successful when we saw that the rice plant was more polite – it had a deep bow,” said Associate Professor Shin-ichi Arimura, joking about how a fertile rice plant bends under the weight of heavy seeds.

Arimura is an expert in plant molecular genetics at the University of Tokyo and led the research team, whose results were published in Nature Plants. Collaborators at Tohoku University and Tamagawa University also contributed to the research.

Genetic diversity for the food supply

Researchers hope to use the technique to address the current lack of mitochondrial genetic diversity in crops, a potentially devastating weak point in our food supply.

In 1970, a fungal infection arrived on Texas corn farms and was exacerbated by a gene in the corn’s mitochondria. All corn on the farms had the same gene, so none were resistant to the infection. Fifteen percent of the entire American corn crop was killed that year. Corn with that specific mitochondrial gene has not been planted since.

“We still have a big risk now because there are so few plant mitochondrial genomes used in the world. I would like to use our ability to manipulate plant mitochondrial DNA to add diversity,” said Arimura.

Plants without pollen

Most farmers do not save seeds from their harvest to replant next year. Hybrid plants, the first-generation offspring of two genetically different parent subspecies, are usually hardier and more productive.

To ensure farmers have fresh, first-generation hybrid seeds each season, agricultural supply companies produce seeds through a separate breeding process using two different parent subspecies. One of those parents is male infertile – it cannot make pollen.

Researchers refer to a common type of plant male infertility as cytoplasmic male sterility (CMS). CMS is a rare but naturally occurring phenomenon caused primarily by genes not in the nucleus of the cells, but rather the mitochondria.

Green beans, beets, carrots, corn, onions, petunia, rapeseed (canola) oil, rice, rye, sorghum, and sunflowers can be grown commercially using parent subspecies with CMS-type male infertility.

Beyond green

Plants use sunlight to produce most of their energy, through photosynthesis in green-pigmented chloroplasts. However, chloroplasts’ fame is overrated, according to Arimura.

“Most of a plant isn’t green, only the leaves above the ground. And many plants don’t have leaves for half the year,” said Arimura.

Plants get a significant portion of their energy through the same “powerhouse of the cell” that produces energy in animal cells: the mitochondria.

“No plant mitochondria, no life,” said Arimura.

Mitochondria contain DNA completely separate from the cell’s main DNA, which is stored in the nucleus. Nuclear DNA is the long double-helix genetic material inherited from both parents. The mitochondrial genome is circular, contains far fewer genes, and is primarily inherited only from mothers.

The animal mitochondrial genome is a relatively small molecule contained in a single circular structure with remarkable conservation between species.

“Even a fish’s mitochondrial genome is similar to a human’s,” said Arimura.

Plant mitochondrial genomes are a different story.

“The plant mitochondrial genome is huge in comparison, the structure is much more complicated, the genes are sometimes duplicated, the gene expression mechanisms are not well-understood, and some mitochondria have no genomes at all – in our previous studies, we observed that they fuse with other mitochondria to exchange protein products and then separate again,” said Arimura.

Manipulating plant mitochondrial DNA

To find a way to manipulate the complex plant mitochondrial genome, Arimura turned to collaborators familiar with the CMS systems in rice and rapeseed (canola). Prior research strongly suggested that in both plants, the cause of CMS was a single, evolutionarily unrelated mitochondrial gene in rice and in rapeseed (canola): clear targets in the perplexing maze of plant mitochondrial genomes.

Arimura‘s team adapted a technique that had previously edited mitochondrial genomes of animal cells growing in a dish. The technique, called mitoTALENs, uses a single protein to locate the mitochondrial genome, cut the DNA at the desired gene, and delete it.

“While deleting most genes creates problems, deleting a CMS gene solves a problem for plants. Without the CMS gene, plants are fertile again,” said Arimura.

The fully fertile four new lines of rice and three new lines of rapeseed (canola) that researchers created are a proof of concept that the mitoTALENs system can successfully manipulate even the complex plant mitochondrial genome.

“This is an important first step for plant mitochondrial research,” said Arimura.

Researchers will study the mitochondrial genes responsible for plant male infertility in more detail and identify potential mutations that could add much-needed diversity.

Read the paper: Nature Plants

Article source: University of Tokyo

Image: Tomohiko Kazama

Even in jagged volcanic ice spires, life (i.e. snow algae) finds a way

By | News, Plant Science

High in the Andes Mountains, dagger-shaped ice spires house thriving microbial communities, offering an oasis for life in one of Earth’s harshest environments as well as a possible analogue for life on other planets.

The distinctive icy blade formations known as nieves penitentes (or, “penitent ones”) are named for their resemblance to praying monks in white robes and form in cold, dry conditions at elevations above 13,000 feet. The penitentes, which can range from a few inches to 15 feet high, are found in some of the most hostile conditions on Earth, with extreme winds, temperature fluctuations and high UV radiation exposure due to the thin atmosphere.

And yet, as a recently published study led by CU Boulder student researchers finds, these spires offer shelter for microbes by providing a water source in an otherwise arid, nutrient-poor environment.

In March 2016, CU Boulder students and faculty members traveled to Volcán Llullaillaco in Chile, the world’s second-highest volcano. The two-week expedition into the arid landscape, planned in collaboration with their Chilean colleagues, was no easy feat.

“This is a very remote area that’s difficult to access,” said Steve Schmidt, a professor in CU Boulder’s Department of Ecology and Evolutionary Biology (EBIO) and a co-author of the study. “The entire back of one of our pickup trucks had to be filled with barrels of drinking water. It’s no trivial thing to go out there, and that’s one of the reasons these formations haven’t been studied much.”

After reaching the penitente fields at 16,000 feet above sea level, the scientists noticed patches of red coloration, a telltale sign of microbial activity that has been previously observed in other snow and ice formations around the world.

Upon bringing back samples for analysis, the researchers confirmed the presence of algal species Chlamydomonas and Chloromonas in the ice, the first documentation of snow algae or any other life forms in the penitentes.

“Snow algae have been commonly found throughout the cryosphere on both ice and snow patches, but our finding demonstrated their presence for the first time at the extreme elevation of a hyper-arid site,” said Lara Vimercati, lead author of the study and a doctoral researcher in EBIO. “Interestingly, most of the snow algae found at this site are closely related to other known snow algae from alpine and polar environments.”

The new findings add to scientists’ understanding of the limits of life on Earth, says Alexandra Krinsky, a co-author of the study and an undergraduate in the Department of Molecular, Cellular and Developmental Biology who helped analyze the samples.

“From looking at the extreme environments of the dry Andes to the aquatic life roaming the sea floor, we have broken the original ideas of where life can and has been found,” she said.

The study may also have implications for the search for alien life. Penitente-like formations have recently been discovered on Pluto and are speculated to exist on Europa, one of Jupiter’s moons. The Atacama region in Chile is also considered to be the best Earth analogue for the soils of Mars.

“We’re generally interested in the adaptations of organisms to extreme environments,” Schmidt said. “This could be a good place to look for upper limits of life.”

“Our study shows how no matter how challenging the environmental conditions, life finds a way when there is availability of liquid water,” Vimercati said.

Additional co-authors of the research include Adam Solon of CU Boulder; John Darcy of the University of Colorado Denver; Dorota Porazinska of the University of Florida; and Pablo Arán and Cristina Dorador of the Universidad de Antofagasta (Chile).

Read the paper: Arctic, Antarctic, and Alpine Research

Article source: University of Colorado at Boulder

Image: Steve Schmidt/CU Boulder

These algae can live inside fungi. It could be how land plants first evolved.

By | News, Plant Science

Picture a typical documentary scene on the evolution of life. It probably starts with little bugs in a murky, primordial soup. Eons of time zip by as bugs turn into fish, fish swim to land as their fins morph into limbs for crawling animals, which then stand up on two legs, to finally end up with walking humans.

The picture is very animal-centric. But what about plants? They also made the jump from water to land. Scientists think that green algae are their water-living ancestors, but we are not sure how the transition to land plants happened.

New research from Michigan State University, and published in the journal eLife, presents evidence that algae could have piggybacked on fungi to leave the water and to colonize the land, over 500 million years ago.

“Fungi are found all over the planet. They create symbiotic relationships with most land plants. That is one reason we think they were essential for evolution of life on land. But until now, we have not seen evidence of fungi internalizing living algae,” says Zhi-Yan Du, study co-author and member of the labs of Christoph Benning, and now, Gregory Bonito.

Researchers selected a strain of soil fungus and marine alga from old lineages, respectively Mortierella elongata and Nannochloropsis oceanica.

When grown together, both organisms form a strong relationship.

“Microscopy images show the algal cells aggregating around and attaching to fungal cells,” Du says. “The algal wall is slightly broken down, and its fibrous extensions appear to grab the surface of the fungus.”

Surprisingly, when they are grown together for a long time – around a month – some algal cells enter the fungal cells. Both organisms remain active and healthy in this relationship.

This is the first time scientists have seen fungi internalize a expand iconeukaryotic, photosynthetic organism. They call it a ‘photosynthetic mycelium’.

“Both organisms get additional benefits from being together,” Du says. “They exchange nutrients, with a likely net flow of carbon from alga to fungus, and a net flow of nitrogen in the other direction. Interestingly, the fungus needs physical contact with living algal cells to get nutrients. Algal cells don’t need physical contact or living fungus to benefit from the interaction. Fungal cells, dead or alive, release nutrients in their surroundings.”

“Even better, when nutrients are scarce, algal and fungal cells grown together fend off starvation by feeding each other. They do better than when they are grown separately.”

Perhaps this increased hardiness explains how algae survived the trek onto land.

“In nature, similar symbiotic events might be going on, more than we realize,” Du adds. “We now have a system to study how a expand iconphotosynthetic organism can live inside a non-photosynthetic one and how this symbiosis evolves and functions.”

Both organisms are biotech related strains because they produce high amounts of oil. Du is testing them as a platform to produce high-value compounds, such as biofuels or Omega 3 fatty acids.

“Because the two organisms are more resilient together, they might better survive the stresses of bioproduction,” Du says. “We could also lower the cost of harvesting algae, which is a large reason biofuel costs are still prohibitive.”

Read the paper: eLife

Article source: MSU-DOE Plant Research Laboratory

Image: Zhi-Yan Du, colored by Igor Houwat; from eLife

Improved model could help scientists better predict crop yield, climate change effects

By | Climate change, News, Plant Science

A new computer model incorporates how microscopic pores on leaves may open in response to light—an advance that could help scientists create virtual plants to predict how higher temperatures and rising levels of carbon dioxide will affect food crops, according to a study published in a special issue of the journal Photosynthesis Research.

“This is an exciting new computer model that could help us make much more accurate predictions across a wide range of conditions,” said Johannes Kromdijk, who led the work as part of an international research project called Realizing Increased Photosynthetic Efficiency RIPE.

RIPE, which is led by the University of Illinois, is engineering crops to be more productive without using more water by improving photosynthesis, the natural process all plants utilize to convert sunlight into energy to fuel growth and crop yields. RIPE is supported by the Bill & Melinda Gates Foundation, the U.S. Foundation for Food and Agriculture Research (FFAR), and the U.K. Government’s Department for International Development (DFID).

The current work focused on simulating the behavior of what are known as stomata—microscopic pores in leaves that, in response to light, open to allow water, carbon dioxide, and oxygen to enter and exit the plant. In 2018, the RIPE team published a paper in Nature Communications that showed increasing one specific protein could prompt plants to close their stomata partially—to a point where photosynthesis was unaffected, but water loss decreased significantly. This study’s experimental data was used to create the newly improved stomata model introduced today.

“We’ve known for decades that photosynthesis and stomatal opening are closely coordinated, but just how this works has remained uncertain,” said Stephen Long, Ikenberry Endowed University Chair of Crop Sciences and Plant Biology at the University of Illinois. “With this new computer model, we have a much better tool for calculating stomatal movements in response to light.”

The ultimate goal, Long said, is to identify opportunities to control these stomatal gatekeepers to make drought-tolerant crops. “Now we’re closing in on the missing link: How photosynthesis tells stomates when to open.”

Computer modeling has been a major advance in crop breeding. The father of modern genetics, Gregor Mendel, made his breakthrough discovery that pea plants inherit traits from their parents by growing and breeding more than 10,000 pea plants over eight years. Today, plant scientists can virtually grow thousands of crops in a matter of seconds using these complex computer models that simulate plant growth.

Stomatal models are used together with models for photosynthesis to make wide-ranging predictions from future crop yields to crop management, such as how crops respond when there is a water deficit. In addition, these models can give scientists a preview of how crops like wheat, maize, or rice could be affected by rising carbon dioxide levels and higher temperatures.

“The previous version of the stomatal model used a relationship that wasn’t consistent with our current understanding of stomatal movements,” said Kromdijk, now a University Lecturer at the University of Cambridge. “We found that our new version needs far less tuning to make highly accurate predictions.”

Still, there’s a lot of work to be done to show that this modified model functions in a wide variety of applications and to underpin the relationship between stomata and photosynthesis further.

“We have to show that this model works for a diverse range of species and locations,” said former RIPE member Katarzyna Glowacka, now an assistant professor at the University of Nebraska-Lincoln. “Large-scale simulation models string together models for atmospheric turbulence, light interception, soil water availability, and others—so we have to convince several research communities that this is an improvement that is worth making.”

Read the paper: Photosynthesis Research

Article source: University of Illinois College of Agricultural, Consumer and Environmental Sciences ACES

Image: Brian Stauffer/University of Illinois