Category

Plant Science

saisies

Daisies that close at night have camouflaged petals to protect them from herbivores

By | News, Plant Science

Species of daisy that close their flowers at night, produce colour in their exposed lower petals that makes them harder to spot for herbivores, reducing herbivory rates of flowers. The findings are presented in the British Ecological Society journal Functional Ecology.

Researchers from Stellenbosch University, South Africa found that tortoises, one of the main herbivores of the daisies, were unable to distinguish the lower petal surfaces against a green leaf background. Tortoises prefer to eat protein-rich flowers over leaves, but when confronted with closed flowers, they showed no preference between them.

When the researchers modelled the colours of the lower petal surfaces in the vision of other herbivores, they also found these colours to be indistinguishable from leaves.

In contrast, species of daisy that do not close at night produced the same colouration on their lower petals as the upper petals exposed to pollinators.

Plants face an evolutionary conflict between having flowers that attract pollinators while avoiding herbivores. Often plants defend themselves chemically, but this can have adverse effects on pollination.

“When plants defend their flowers chemically, the pollination interactions can be negatively influenced. Our study shows a novel way in which flowers can avoid herbivores, without compromising pollination interactions.

– says Dr. Jurene Kemp, lead author of the study.

“These flowers can potentially circumvent the conflict of attracting both pollinators and herbivores by producing attractive colours on the surfaces that are exposed to pollinators (when flowers are open) and cryptic colours that are exposed when herbivores are active (when flowers are closed).”

In Namaqualand, South Africa, where the research took place, daises bloom annually in a spring flowering. This makes preserving flowers, responsible for reproduction, particularly important.

The researchers examined the colouration of 77 Asteraceae species, modelling how they appear in the visual systems of chameleons, horses and goats as proxies for tortoises and larger herbivores in the area, like springbok. They then tested the preferences of real tortoises with both open and closed flowers against leaf backgrounds.

Not all Asteraceae species that close their flowers had cryptically coloured lower petal surfaces, but in the experiments, the tortoises did not readily eat these flowers. Dr. Kemp said, “One interesting question would be to test whether non-cryptic flowers have chemical defences, and whether these chemical defences are absent in the cryptic flowers.”

On further research Dr. Kemp said “Unfortunately, we could only do this using one plant family in one botanical region, it would be great to see if other plant species also use colour to avoid herbivores.”

The researchers would also have liked to use larger herbivores such as springboks in their behavioural experiments, but Dr. Kemp adds that “this was practically not possible.”

Read the paper: Functional Ecology

Article source: British Ecological society Press Office

Image: Jurene Kemp


Spillover from remnant grasslands enhances plant diversity in restorations but the effect is context dependent and driven by wind-dispersed seeds, such as milkweed.

Grassland biodiversity is blowing in the wind

By | News, Plant Science

Temperate grasslands are the most endangered but least protected ecosystems on Earth. Grassland restorations are crucial for recovering this important but highly degraded ecosystem. Restored grasslands, however, tend to be more species poor and lose diversity through time as compared to remnant, or never-been plowed, grasslands.

Read More
phytoplankton

Phytoplankton more resilient to nutrient stress than previously thought

By | News, Plant Science, Research

An international team of Earth system scientists and oceanographers has created the first high-resolution global map of surface ocean phosphate, a key mineral supporting the aquatic food chain. In doing so, the University of California, Irvine-led group learned that marine phytoplankton – which rely on the trace nutrient – are a lot more resilient to its scarcity than previously thought.

The researchers’ findings, published today in Science Advances, have important implications for climate change predictions. Ocean algae, or phytoplankton, absorbs a significant amount of carbon dioxide from the Earth’s atmosphere, thereby providing a valuable service in regulating the planet’s temperature.

“Understanding the global distribution of ocean nutrients is fundamental to identifying the link between changes in ocean physics and ocean biology,” said lead author Adam Martiny, UCI professor of Earth system science and ecology & evolutionary biology. “One of the outcomes of having this map is that we can show that plankton communities are extremely resilient even in nutrient-deficient environments. As lower ocean nutrient availability is one of the predicted outcomes of climate change, this may be good news for plankton – and for us.”

Dissolved inorganic phosphate plays an important biogeochemical role in the ocean habitat but is notoriously difficult to detect. Phosphorus is a crucial element of essential-to-life molecules such as adenosine triphosphate, which stores and transfers chemical energy between cells, and those found in DNA. Earth has a finite amount of phosphorus – unlike many other nutrients useful to phytoplankton – and it’s rare in the ocean.

Knowing how much is out there, and where, helps scientists understand the dynamics of the ocean food web and how it will be affected by alterations in ocean chemistry brought on by climate change. Martiny and his colleagues analyzed more than 50,500 seawater samples collected on 42 research voyages covering all of Earth’s ocean basins.

Martiny said that in addition to identifying regions where the mineral is in short supply, the team was able to discover previously unknown patterns of phosphate levels in major ocean basins in the Atlantic and Pacific.

“We have for too long had this simplistic view of a nutrient-rich ocean at high latitudes and ocean deserts at low latitudes,” he said. “However, in this paper we argue that our current predictions of nutrient stress may be too dire and that marine organisms are able to handle a limited supply of phosphate better than we previously thought.”

Read the paper: Science Advances

Article source: University of California – Irvine

Image: ! ツ / Pixabay

CABMV symptoms

Technique combats widespread passion fruit disease

By | News, Plant Health, Plant Science, Research

Passion fruit woodiness caused by cowpea aphid-borne mosaic virus (CABMV), the disease that most affects passion fruit (Passiflora edulis) grown in Brazil, can be combated with a relatively simple technique.

A study published in the journal Plant Pathology shows that systematic eradication of plants with symptoms of the disease preserves the crop as a whole and keeps plants producing for at least 25 months.

The technique currently used to combat CABMV entails renewing the entire orchard every year. This is, of course, a costly procedure. According to the authors of the study, economic factors are critical for this crop, which is mostly grown by small producers.

CABMV occurs in all states of Brazil and impairs plant development. Passion fruit woodiness disease causes leaf mosaic, blisters, deformation and reduced fruit size, making the produce unmarketable. Vines are typically eliminated only when the disease is detected in the early stages of their life cycle. The researchers propose systematic roguing – removal of weak, diseased or abnormal plants – throughout the life of the crop.

The study was funded by FAPESP and CAPES, the Brazilian Ministry of Education’s Coordination for the Improvement of Higher Education Personnel. It was conducted by Brazilian researchers affiliated with the University of São Paulo’s Luiz de Queiroz College of Agriculture (ESALQ-USP), the Federal University of São Carlos (UFSCar) at Araras, the University of Southwest Bahia (UESB), and the Semiarid Agriculture Unit of the Brazilian Agricultural Research Corporation (EMBRAPA), as well as colleagues at Argentina’s National Agricultural Technology Institute (INTA).
“Roguing is a technique that has been used to combat papaya disease in Espírito Santo state since the 1980s. After several experiments, it was found to be the best way to control papaya ringspot virus type P [PRSV-P],” said Jorge Alberto Marques Rezende, Full Professor at ESALQ-USP and principal investigator for the study, which began in 2010.

CABMV is transmitted by aphid saliva and spreads throughout an orchard in a few months. The aphid species in question do not colonize the plants but merely visit them, and insecticide is not effective for control purposes.
“Insecticide affects their nervous system but takes hours to kill them. Meanwhile, they’re stimulated to feed on more plants, spreading the virus farther, so insecticide helps propagate the disease instead of controlling it,” said David Marques de Almeida Spadotti, first author of the article. The research was part of Spadotti’s postdoctoral fellowship at ESALQ-USP.
In previous experiments, the use of transgenic passion fruit plants and inoculation with attenuated variants of CABMV as a kind of vaccine also failed to control the disease. In this new study, an experimental orchard was planted in three areas belonging to ESALQ-USP in Piracicaba, São Paulo state, and two areas in Vitória da Conquista, southwestern Bahia. The experiments took place between 2013 and 2018. Approximately 100 healthy seedlings were planted in two areas of each city using trellises or T-shaped arbors connected by wires.

The vines were trained on the trellises and arbors for support but also to separate them so that the disease could easily be observed. Any buds with symptoms were identified and removed in weekly inspections.
In two other areas distant from the others, the same number of vines were planted using trellises and allowed to interlace without roguing, as in commercial plantations. The results of the two strategies were then compared.

In the absence of roguing, the virus spread throughout the crop in 120 days. In the areas submitted to systematic roguing, 8% of the vines were infected and removed after 180 days. In Piracicaba, only 16% had to be removed after 25 months, and the plants remained productive throughout this period.

The presence of CABMV in all infected or preventively removed vines was confirmed by PTA-ELISA serological testing.

“The symptoms appear eight days after inoculation of the virus on average. Roguing enables the grower to identify diseased plants visually and base control on visual inspection. Inspection should ideally be carried out at least once a week”

Spadotti said.

Cultural change

According to the researchers, the next step in the study entails larger pilot plantings of 1,000-2,000 passion fruit vines. In addition to eradicating diseased plants, they plan to replace them with healthy plants. The idea is to maintain the orchard for three to four years and compare it with another orchard maintained in the conventional manner, in which all plants are replaced every year.

“Because passion fruit is semiperennial, this longer production period is more advantageous from an economic standpoint than complete annual substitution,” said Rezende, principal investigator for the Thematic Project “Begomovirus and Crinivirus in Solanaceae”, which also relates to viruses in food crops.

The researchers stress, however, that if the strategy is to succeed, it should be implemented by all passion fruit growers in any given region. In addition to other plantations, the virus can spread from old or abandoned orchards, which should be eliminated.

CABMV-susceptible wild species of passion fruit in forests near plantations may also spread the disease. One of the experimental areas in Vitória da Conquista failed for this reason. When the wild plants were eliminated, the incidence of CABMV was considerably reduced.

According to IBGE, the national statistics and census bureau, Brazil is the world’s leading grower of passion fruit, with more than 550,000 metric tons produced in 2017.

Read the paper: Plant Pathology

Article source: Agência FAPESP

Author: André Julião

Image: Jorge Rezende

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