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Plants grow less in hotter temperatures

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Plants have developed a robust system that stops their cell cycle in hostile environments such as abnormally hot temperatures. In response, they direct their energy to survival rather than growth. A new study led by scientists at the Nara Institute of Science and Technology (NAIST) reports in eLife that two transcription factors, ANAC044 and ANAC085, are critical for this response in the flowering plant Arabidopsis. The findings give clues on ways to modulate the growth of crops and other agriculture products.

Upon DNA damage, plants and animals halt cell division and execute DNA repair. This response prevents the damaged cells from proliferating. NAIST Professor Masaaki Umeda has made a career studying the molecular biology behind this protective measure.

“We reported that SOG1 is activated by DNA damage and regulates almost all genes induced by the damage,” he says. Another study from the lab showed “Rep-MYBs are stabilized in DNA damage conditions to suppress cell division,” he adds.

In the laboratory’s newest study, Umeda’s research team shows that ANAC044 and ANAC085 act as a bridge between SOG1 and Rep-MYB.

The scientists disrupted DNA in Arabidopsis cells by treating the cells with bleomycin, a compound commonly used to halt the growth of human cancer cells. The Arabidopsis cells failed to proliferate as expected unless they possessed a mutation in ANAC044 or ANAC085. In the mutant cases, the cells proliferated as though they were never exposed to bleomycin.

“We found that ANAC044 and ANAC085 are essential for root growth retardation and stem cell death, but not for DNA repair,” says Umeda.

Specifically, ANAC044 and ANAC085 were responsible for preventing the cell cycle from proceeding from G2 phase to mitosis in response to the DNA damage.

Rep-MYBs cause the same arrest in the cell cycle. Consistently, in normal cells, bleomycin caused a rise in the accumulation of Rep-MYBs, but not in cells with ANAC044 and ANAC085 mutations. These findings suggest ANAC044 and ANAC085 act as a bridge between SOG1 and Rep-MYBs in the halting of the cell cycle upon DNA damage.

DNA damage is just one form of stress that can cause the cell cycle to pause. To investigate whether ANAC044 and ANAC085 act in response to other forms of external stress, the researchers exposed the cells to different temperatures and osmotic pressure which cause the retardation in G2 and G1 progression, respectively.

Growth arrest was observed in both mutant and normal cells at a high osmotic pressure, but higher temperatures only caused pauses in the cell cycle in normal cells, indicating that ANAC044 and ANAC085 act as gatekeepers in the progression from the G2 phase in the cell cycle under abiotic stress conditions.

The fact that ANAC044 and ANAC085 operate in response to different types of abiotic stress suggests to Umeda that they may be at the core of new technologies designed to modulate plant growth.

“The research illuminates a new mechanism that optimizes organ growth under stressful conditions. When trying to increase plant productivity, scientists should consider ANAC044 and ANAC085,” he says.

Read the paper: eLife

Article source: Nara Institute of Science and Technology (NAIST)

Image: Masaaki Umeda

Insect-deterring sorghum compounds may be eco-friendly pesticide

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Compounds produced by sorghum plants to defend against insect feeding could be isolated, synthesized and used as a targeted, nontoxic insect deterrent, according to researchers who studied plant-insect interactions that included field, greenhouse and laboratory components.

The researchers examined the role of sorghum chemicals called flavonoids –specifically 3-deoxyflavonoid and 3-deoxyanthocyanidins — in providing resistance against the corn leaf aphid, a tiny blue-green insect that sucks sap from plants. To defend against pests like the aphids, sorghum has evolved defenses that includes biosynthesis of secondary metabolites, including flavonoids to poison the pests.

A previous Penn State study showed that in sorghum, accumulation of these flavonoids is regulated by a gene called yellow seed1 that controls responses to stresses such as fungal pathogens, noted Surinder Chopra, professor of maize genetics, Penn State. His research group in the College of Agricultural Sciences led both studies.

In the current research carried out at the University’s Russell E. Larson Agricultural Research Center, researchers grew two nearly identical lines of sorghum — one with a functional _y1_ gene that produced flavonoids, and the other a mutant called null y1, which did not possess the functional yellow seed1 gene responsible for producing the flavonoids.

When they compared the two lines of plants, researchers found that a significantly higher number of adult corn-leaf aphids colonized null y1 plants compared to the plants with functional _y1_ gene that produced flavonoids. The aphids actively fed on the null y1 plants to where some of them showed signs of stress with yellowed leaves. The functional sorghum plants that produced the flavonoids had much lower aphid numbers and showed no ill effects from aphid feeding.

Greenhouse experiments with similar potted sorghum plants demonstrated that the aphids clearly preferred to feed and reproduce on null y1 plants, and the adults produced many more nymphs.

In a companion laboratory experiment, researchers fed two groups of adult aphids diets of sorghum leaf tissues — but to one they added an extract containing the flavonoids. After a few days, most of the aphids that fed on the flavonoid-enriched leaf tissue died and reproduction was curtailed — none of those aphids had nymphs before they succumbed.

Perhaps surprisingly, Chopra explained, the flavonoids are not present in the phloem — vascular tissue in plants that conducts the sugars aphids seek — but are in the epidermal cells that form the outermost layer of defense. When aphids repeatedly probe and puncture the epidermal cells with their stylets, or beaks, they take up the flavonoids that lead to their demise.

The findings, published online in the Journal of Chemical Ecology, indicate flavonoids can potentially be deployed as potent insect deterrents to protect crops, Chopra suggested.

“Sorghum plants have evolved to precisely emit compounds offering defenses against harmful predatory insects that threaten them, and yet these chemicals in their defenses don’t hurt beneficial insects,” said Chopra. “If we could develop nontoxic insecticides, it would be a game changer — given that the toxicity of synthetic pesticides is of great concern, and they are considered to be dangerous to human health.”

Chopra, supported by Penn State, has applied for a patent on using flavonoids as insect deterrents. He pointed out that while much more research needs to be done, the most important consideration is that flavonoids are natural plant products that do not cause any pollution and are not harmful to human or animal health.

This research may be an early step toward developing new phytochemicals for crop defenses, Chopra believes. “How well the flavonoids work against other herbivores is being researched, but we know with corn leaf aphids they are very, very potent,” he said.

Read the paper: Journal of Chemical Ecology

Article source: Penn State

Image: USDA

New Pathways for Sustainable Agriculture

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Hedges, flowering strips and other seminatural habitats provide food and nesting places for insects and birds in agricultural landscapes. This also has advantages for agriculture: bees, flies, beetles and other animal groups pollinate crops and control pest insects in adjacent fields.

But how much of these habitats is necessary and how should they be arranged to make use of these nature-based ecosystem services?

This question has been addressed by a new study from the Chair of Animal Ecology and Tropical Biology at the Biocenter of Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany. The results are published in the journal “Ecology Letters”.

Small-scale land use is advantageous

According to the study, biodiversity, pollination, and pest control can be improved in landscapes even with a relatively small amount of non-crop habitat. To reach this effect, these habitats must be arranged to create a small-scale agricultural landscape.

For this study, Dr. Emily A. Martin‘s team took a closer look at data from ten European countries and 1,515 different agricultural landscapes. This clearly showed that small-scale land use is advantageous: it leads to a greater density of beneficial insects and spiders. And it increases the services provided by ecosystems for agriculture – pollination and natural pest control.

Creating a web of seminatural habitats

“In order to reduce pests and promote biodiversity, increasing the density of seminatural habitat elements can be an ideal solution for farms. You don’t have to remove much land from cultivation to reach a significant effect,” says Dr. Martin.

“The implementation of these findings would be an important step forward in the effort to achieve a sustainable and biodiversity-friendly agriculture”, Professor Ingolf Steffan-Dewenter, head of the Chair of Animal Ecology and Tropical Biology and co-author of the study, emphasises.

The JMU research team is now focusing on intensified cooperation with agricultural and environmental stakeholders. The scientists want to help implement a landscape management system that benefits everyone – nature and mankind.

Read the paper: Ecology Letters

Article source: University of Würzburg

Image: Matthias Tschumi

Knowing how cells grow and divide can lead to more robust and productive plants

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A large portion of a plant is hidden below the ground. This buried root system is essential for the plant: it provides stability, water, and food. In contrast to mammals, where the body plan is final at birth, the formation of new root branches ensures that the root system keeps growing throughout a plant’s life. The labs of Prof. Ive De Smet and Prof. Tom Beeckman (VIB-UGent Center for Plant Systems Biology), together with researchers from the University of Nottingham (UK), Heidelberg University (Germany) and the University of Copenhagen (Denmark) identified a novel component that controls the development of root branches supporting plants. Their findings will be published in the journal Proceedings of the National Academy of Sciences of the United States of America.

Prof. Ive De Smet and his team investigate how plants deal with changing environments, specifically with temperature extremes and drought stress. Prof. Tom Beeckman and his team explore how (lateral) roots evolved and develop. In plants, new organs are formed all the time. To do this, there must be a tight regulation of when and where a new organ is formed, and of how the cells that will make up this organ need to grow and divide.

To investigate organ formation in plants, the researchers used root branching as a model system. This process occurs continuously along the growing root, endlessly increasing the root system, and requires an extremely fine-tuned coordination of asymmetric cell divisions in cells that can give rise to new roots, together with the synchronization of processes in surrounding tissues. This ensures that the roots grow in the best possible way to take advantage of the nutrients and water in the soil.

Dr. Ramakrishna (University of Nottingham), who is the first author of the study, explains how the team discovered a new component through which plants control this: “To identify novel factors involved in governing root branching, we explored which genes are expressed during the early stages of the process. This led to the identification of a cell wall modifying enzyme – a molecule that regulates chemical reactions – that controls the cell divisions leading to the growth of a new root. Mutations in the gene that codes for this enzyme led to swelling of root cells that give rise to a new lateral root and resulted in subsequent defects in the first asymmetric cell divisions during the formation of root branches.”

These results show that a very tight regulation of cell size impacts the position of cell divisions, and thus the location and growth of new root branches. The identification of a cell wall enzyme acting in the extracellular space mediating plant stem cell divisions suggests we need to take into account a much broader range of proteins in our future search to disentangle the process of root branching.

Prof. Tom Beeckman (VIB-UGent) adds: “Identifying this enzyme is only a first step. The next challenge is to unravel how these cell wall modifications control cell size and how this is coordinated with other molecular processes during root branching.”

Prof. Ive De Smet (VIB-UGent) continues: “Ultimately, we strive to understand how plants respond to their ever-changing environment. Improving root architecture can contribute to stabilization of plant yield under adverse environmental conditions.”

This study, and the new research avenues it opens up, could lead to innovative techniques to improve root architecture in favor of higher crop yields and plants more resistant to drought and nutrient stress.

Read the paper: PNAS

Article source: VIB-UGent

Image: Pixabay

Local plant-microbe alliances shape global biomes

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Dense rainforests, maple-blanketed mountains and sweeping coniferous forests demonstrate the growth and proliferation of trees adapted to specific conditions. The regional dominance of tree species we see on the surface now, however, might actually have been determined underground long ago.

Princeton University researchers report that the organization of forests worldwide — such as conifers in northern boreal forests or the broad-leafed trees of the tropics — are based on the ancient relationships that plant species forged with soil-dwelling microbes such as fungi and bacteria. These tiny organisms, known as symbionts, enhance the roots’ uptake of the crucial nutrients nitrogen and phosphorus.

The researchers reported in the journal Nature Ecology and Evolution that trees and shrubs came to dominate specific biomes by evolving the most competitive arrangement with local soil microbes — and cutting competing plants out of the action.

The biome-specific dynamics between plants and soil microbes could help scientists understand how ecosystems may shift as climate change brings about warmer temperatures that alter the interplay between trees, microbes and soil, the researchers report. Because the most competitive symbiotic arrangements for a particular biome triumph, scientists would only need to understand how an ecosystem is changing to gauge which vegetation will be moving in and which will be moving out. The research was supported by the Carbon Mitigation Initiative based within the Princeton Environmental Institute (PEI).

“The pattern we found can be used to tell us the landscapes that are more sensitive to human disturbance,” said senior author Lars Hedin, the George M. Moffett Professor of Biology and professor of ecology and evolutionary biology and the Princeton Environmental Institute. “It will predict what communities of trees will go where, their effect on the environment, and how they will respond in the future to climate change and increased carbon dioxide.”

First author Mingzhen Lu, a postdoctoral research associate in the Hedin lab, said that symbioses arose because plants needed microbes to unlock the nutrients — particularly nitrogen and phosphorus — released through soil decomposition. In return, the fungi and bacteria thrive on the carbohydrates that plants provide from photosynthesis. Lichen — the frilly white-green algae-fungus amalgamations that grow on rocks and trees — are an early example of this cooperation.

“The moment plants colonized the land, they formed symbioses,” Lu said. “The evolution of those new, powerful symbioses allowed plants to colonize new lands. This biology powers the global carbon and nutrient cycle.”

Lu and Hedin focused on trees and shrubs and found that as the plants spread across the globe, they carved out biomes using the nutrient advantage their relationship with microbes bestowed on them, Lu said. For example, maple trees will set conditions so that competing trees can’t grow in the areas maples inhabit.

“This is a perfect example of how biological organisms can shape the surrounding environment in favor of themselves,” Lu said. “This suggests to us that once the correct biological mechanisms are included, changes in the land can be predicted, but those forecasts need to capture belowground dynamics. By figuring out the most competitive symbiosis under specified conditions, we can determine how plant communities will evolve and develop in that biome in the future.”

Lu and Hedin used a game-theory model that allowed plants to use different belowground strategies for acquiring nutrients. Their model examined trees and shrubs — known as dominant vegetation — in tropical, temperate and boreal forests. They looked at biome conditions such as sunlight and nutrient turnover to examine the most competitive symbioses that will emerge if ecosystems are allowed to change and mutate naturally. They factored in the amount of carbon and nutrients that cycle through a particular biome, as well as how it responds to disturbances and how plant populations replace each other through succession.

Their model revealed that specific local interactions between plants, soil and nutrients are suitable for those areas. For instance, boreal trees have developed symbiotic relationships tailored for spongy boreal soils, but not the sodden soil of a tropical forest.

“Our findings show that the relationship between plants and their symbionts is central to understanding the organization and history of the land biosphere,” Hedin said.

The Hedin lab at Princeton previously found that plants may have a more active role in their evolution — and the formation of natural systems — than they are given credit for. In February 2018, Hedin and Lu reported in the journal Natur that the proliferation of plant life across the globe may have been propelled by root adaptations that allowed plants to become more efficient and independent.

In 2015, a paper in Nature Plants suggested that plants found in areas otherwise unsuitable for them — such as nitrogen-poor rainforest soils — use secretions to invite soil bacteria known as rhizobia to infect their roots cells. In a give-give relationship similar to that described in the latest publication, the rhizobia convert atmospheric nitrogen into fertilizer in exchange for carbohydrates. This interplay creates a nitrogen cycle that benefits surrounding vegetation.

“Plants have long created the conditions for their own success. What’s important is that we are now better understanding how this works based on our models,” Hedin said.

“Our new model shows that plants have competed for soil resources and in doing so they have harnessed the help of symbiosis and this has made them successful,” he said. “The resulting relationship has been so powerful that not only have they helped other trees and plants, but they also have transformed the environment.”

Read the paper: Nature Ecology and Evolution

Article source: Princeton University

Image: Mingzhen Lu, Princeton Ecology and Evolutionary Biology

In Frontiers in Plant Science: Pre-Crop Values from Satellite Images to Support Diversification of Agriculture

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Pre-crop values for a high number of previous and following crop combinations originating from farmers’ fields are, for the first time, available to support diversification of currently monotonous crop sequencing patterns in agriculture. The groundbreaking method utilizing satellite images was developed by Natural Resources Institute Finland (Luke) in collaboration with Finnish Geospatial Research Institute (FGI).

Luke has developed together with FGI a dynamic method to derive Normalized Difference Vegetation Index (NDVI) values to estimate pre-crop values on a field parcel scale from open Copernicus Sentinel-2 data. “The method is based on estimation of NDVI-gap, which was originally developed for Luke’s Land Use Optimization -tool available for each Finnish farmer on EconomyDoctor-portal”, says Research Professor Pirjo Peltonen-Sainio.

Pre-crop value is a measure that indicates the benefits of a previous crop for a subsequent crop in crop sequencing. Thereby, understanding on pre-crop values facilitates diversification of crop production. This again is a core measure for sustainable intensification of agricultural systems.

Digitalization can replace resource intensive field experimentation

Traditionally, long-term multi-locational field experiments are needed to identify pre-crop values. Such experiments are very resource intensive and therefore, they evaluate pre-crop values only for a limited number of previous and subsequent crops. With the new method data on pre-crop values can be updated and expanded every year, and implemented across continents.

“To develop the novel method, a total of 240.000 NDVI-values were used. With such vast data pre-crop values were determined for an exceptionally high number of previous and subsequent crop combinations”, describes Luke’s Senior Scientist Lauri Jauhiainen.

For the test-region in the South-West of Finland, the pre-crop values ranged from +16% to -16%. Especially grain legumes and rapeseed were valuable as pre-crops, which is well in line with results from field experiments.

Many opportunities – also rising from limitations

The method had some limitations as well. “For example, there is insufficient data on crops mostly cultivated in monoculture rotations for estimation of the value of a high number of alternative previous crops”, says Peltonen-Sainio. This was especially true for potatoes and sugar beet in Finland, for which spring and winter cereals were the only pre-crops with sufficient data for their pre-crop values.

“Data on pre-crop values can, however, be updated and regionally expanded every year. Now we just concentrated on developing the method per se”, reminds Jauhiainen. Scarce knowledge on pre-crop choices may limit farmers’ actions towards diversification of monotonous potato and sugar beet sequencing. On the other hand, these findings emphasize that the future experiments should focus on estimating pre-crop values for such previous and following crop combinations which suffer from insufficient on-farm data.

Read the paper: Frontiers in Plant Science

Article source: Natural Resources Institute Finland (Luke)

Image: CCO Public domain

Editing of RNA may play a role in chloroplast-to-nucleus communication

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What will a three-degree-warmer world look like? How will plants fare in more extreme weather conditions? When experiencing stress or damage from various sources, plants use chloroplast-to-nucleus communication to regulate gene expression and help them cope.

Now, Salk Institute researchers have found that GUN1—a gene that integrates numerous chloroplast-to-nucleus retrograde signaling pathways—also plays an important role in how proteins are made in damaged chloroplasts, which provides a new insight into how plants respond to stress. The paper was published in the Proceedings of the National Academy of Sciences (PNAS), and may help biologists breed plants that can better withstand environmental stressors.

“Climate change holds the potential to affect our food system dramatically. When plants are stressed, like in a drought, they produce lower crop yields. If we understand how plants respond to stress, then perhaps we can develop a way to increase their resistance and keep food production high,” says Salk Professor Joanne Chory, director of the Plant Molecular and Cellular Biology Laboratory and senior author of the paper.

In plant cells, structures called chloroplasts convert energy from sunlight into chemical energy (photosynthesis). Normally, the nucleus of the cell transmits information to the chloroplasts to maintain steady energy production. However, in a stressful environment, chloroplasts send an alarm back to the cell nucleus using retrograde signaling (creating a chloroplast-to-nucleus communication feedback loop). This SOS prompts a response that helps regulate gene expression in the chloroplasts and the nucleus to optimize energy production from sunlight.

Previously, the Chory lab identified a group of genes, including GUN1, that influence other genes’ expression in the cell when the plant experiences stress. GUN1 accumulates under stressful conditions but the exact molecular function of GUN1 has been difficult to decipher, until now.

“Plants often experience environmental stressors, so there must be a chloroplast-to-nucleus communication pathway that helps the plant know when to conserve energy when injury occurs,” says Xiaobo Zhao, first author and postdoctoral fellow in Chory’s lab. “GUN1 turns out to play a big role in this.”

To understand how GUN1 regulates chloroplast-to-nucleus communication, the scientists observed plants with functional and nonfunctional GUN1 under pharmacological treatments that could damage chloroplasts. In plants without GUN1, gene expression changed, as did RNA editing in chloroplasts. (RNA editing is a modification of the RNA that changes the identity of nucleotides, so that the information in the mature RNA differs from that defined in the genome, altering the instructions for making proteins.) Some areas of RNA had more editing and other locations had less editing—suggesting that GUN1 plays a role in regulating chloroplast RNA editing.

After further analysis, the team unexpectedly found that GUN1 partners with another protein, MORF2 (an essential component of the plant RNA editing complex), to affect the efficiency of RNA editing during chloroplast-to-nucleus communication in damaged chloroplasts. Greater activity of MORF2 led to widespread editing changes as well as defects in chloroplast and leaf development even under normal growth conditions (see image). During periods of stress and injury, MORF2 overproduction also led to disruption of chloroplast-to-nucleus communication.

“Taken together, these findings suggest a possible link between chloroplast-to-nucleus communication and chloroplast RNA editing, which are important regulatory functions for flowering plants, especially during stress,” says Chory, Howard Hughes Medical Institute investigator and holder of the Howard H. and Maryam R. Newman Chair in Plant Biology.

Next, the researchers plan to examine the mechanism of how the RNA editing changes in chloroplasts activate signals that can be relayed to the nucleus, and how these modifications alter the ability of the plant to respond to stress.

Other authors included Jianyan Huang, a postdoctoral fellow in the Chory lab.

Read the paper: PNAS

Article source: The Salk Institute

Image: Salk Institute

Interplay of Pollinators and Pests Influences Plant Evolution

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Brassica rapa plants pollinated by bumblebees evolve more attractive flowers. But this evolution is compromised if caterpillars attack the plant at the same time. With the bees pollinating them less effectively, the plants increasingly self-pollinate. In a greenhouse evolution experiment, scientists at the University of Zurich have shown just how much the effects of pollinators and pests influence each other.

In nature, plants interact with a whole range of organisms, driving the evolution of their specific characteristics. While pollinators influence floral traits and reproduction, herbivorous insects enhance the plant’s defense mechanisms. Now botanists at the University of Zurich have investigated the way these different interactions influence each other, and how rapidly plants adapt when the combination of selective agents with which they interact changes.

Experimental evolution in real time

In a two-year greenhouse experiment, Florian Schiestl, professor at University of Zurich’s Department of Systematic and Evolutionary Botany, and doctoral candidate Sergio Ramos have demonstrated a powerful interplay between the effects of pollinating insects and those of herbivores. For their experiment they used Brassica rapa, a plant closely related to oilseed rape, interacting with bumblebees and caterpillars as selective agents. Over six generations they subjected four groups of plants to different treatments: with bee pollination only, bee pollination with herbivory (caterpillars), hand pollination without herbivory, and hand pollination with herbivory.

Balance between attraction and defense

After this experimental evolution study, the plants pollinated by bumblebees without herbivory were most attractive to the pollinators: they evolved more fragrant flowers, which tended to be larger. “These plants had adapted to the bees’ preferences during the experiment,” explains Sergio Ramos. By contrast, bee-pollinated plants with herbivory were less attractive, with higher concentrations of defensive toxic metabolites and less fragrant flowers that tended to be smaller. “The caterpillars compromise the evolution of attractive flowers, as plants assign more resources to defense,” says Ramos.

Combined impact on reproduction

The powerful interplay between the effects of bees and caterpillars was also evident in the plants’ reproductive characteristics: In the course of their evolution, for example, the bee-pollinated plants developed a tendency to spontaneously self-pollinate when they were simultaneously damaged by caterpillars. Plants attacked by caterpillars developed less attractive flowers, which affected the behavior of the bees so that they pollinated these flowers less well.

Better understanding of the mechanisms of evolution

The study shows the importance of interactive effects in the evolution of diversity. If the combination of selective agents changes, for example through loss of habitat, climate change, or a decline in pollinators, it can trigger rapid evolutionary change in plants. “The environmental changes caused by humans affect the evolutionary fate of many organisms. This has implications in terms of ecosystem stability, loss of biodiversity, and food safety,” says Florian Schiestl. He believes that an understanding of these mechanisms has never been more important than it is now.

Read the paper: Science

Article source: University of Zurich

Image: Florian Schiestl/University of Zurich

To protect stem cells, plants have diverse genetic backup plans

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Despite evolution driving a wide variety of differences, many plants function the same way. Now a new study has revealed the different genetic strategies various flowering plant species use to achieve the same status quo.

In flowering plants, stem cells are critical for survival. Influenced by environmental factors, stem cells direct how and when a plant will grow. Whether a plant needs deep-reaching roots, taller stems, or more leaves and flowers, it is the stem cells that produce new cells for the job.

That’s also why having too many or too few stem cells can disrupt a plant’s growth.

Responsible for all this is a “core genetic circuitry found in all flowering plants,” says Cold Spring Harbor Laboratory Professor and HHMI Investigator Zach Lippman.

In a paper published in Nature Genetics, Lippman and CSHL Professor David Jackson describe the genetic mechanisms that ensure “a deeply conserved stem cell circuit” maintains some function, even if defects occur in a signaling protein called CLV3, and the receptor with which it interacts, CLV1.

“Those players are critical for ensuring a plant has the right number of stem cells throughout life, and we discovered there are backup systems that kick in when these players are compromised through chance mutations,” explains Lippman.

The researchers determined that although the stem cell circuits are essential for flowering plants, the genetic backup systems can vary drastically from plant to plant.

If the gene producing CLV3 is disrupted by a mutation in a tomato, for instance, a related gene will stand in for it. However, Jackson’s team discovered that in the case of maize, two genes are working in parallel to produce the essential signaling protein.

“I like to compare it to a rowboat,” Lippman adds. “In tomato there are two people who can row, but only one is rowing. But if the main rower injures his arm, the second person can take up the oars. In maize, both are rowing all the time, though not necessarily with equal effort. And in Arabidopsis [rockcress] you have one main rower supported by seven, eight, or nine other rowers in the boat; and it looks like only one has a full-size oar. The rest are just using very small paddles.”

“We were surprised to see such big differences”, says Jackson, “but in retrospect it reveals the power of evolution in finding novel ways to protect critical developmental circuits.”

According to Jackson, Lippman and their colleagues, understanding these species-specific strategies for protecting key genetic interactions will be essential for achieving “intelligent crop design” and using genome editing to improve agricultural productivity and sustainability.

Read the paper: Nature Genetics

Article source: Cold Spring Harbor Laboratory

Image: Lippman Lab/Cold Spring Harbor Laboratory

Scientists crack the code to regenerate plant tissues

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Plant regeneration can occur via formation of a mass of pluripotent cells. The process of acquisition of pluripotency involves silencing of genes to remove original tissue memory and priming for activation by external input. Led by Professor Sachihiro Matsunaga from Tokyo University of Science, a team of scientists have shown that plant regenerative capacity requires a certain demethylase that can prime gene expression in response to regenerative cues.

In multicellular organisms, not all genes are expressed in all cells, meaning that not all cells make the same enzymes or proteins, and therefore not all cells have the same metabolism. This differentiation is a key process across multicellular organisms, including plants and fungi. But as cells specialize, they become unipotent, meaning that they lose the ability to form multiple cell types. For long, scientists have tried to reprogram mammal cells for pluripotency by drastic means such as nuclear transfer and induction of transcription factors. However, plants can acquire the same regenerative powers via external signal input such as hormones and stress. A part of the phenomenon is regulated by epigenetics, because these modifications are epi or “above” the genes.

Professor Matsunaga and his team used Arabidopsis thaliana, a small flowering plant commonly used in plant biology, to study genome-wide histone modifications. Histones are proteins that package together eukaryotic DNA, preventing it from being transcribed or decoded. Upon being modified, however, these proteins’ grasp around the DNA molecule loosens, making it easier for the DNA to be transcribed. The group of scientists found that it is the demethylation (the removal of a methyl group from the amino acid) of the histone H3 by the LDL3 enzyme that lends regenerative competency to the plant. This epigenetic mechanism allows the plant’s pluripotent cells to go back to its unipotent state and thus assume the identity of shoot meristems for differentiated tissues including leaves and stems.

Because no seeds are needed to grow these plants, this could potentially help scientists grow plants faster without flowering. “By strengthening the ability of plants to reproduce, even without seeds,” Professor Matsunaga indicated, “it is possible to increase the number of clonal plants with only leaves, stems, and parts of roots. It can address environmental problems by promoting greening and solve the global food shortage problem by increasing production of grains and vegetables.”

Read the paper: Nature Communications

Article source: Tokyo University of Science

Image: Alberto Salguero/Wikimedia