Eco-Update

News on Food, Farming, Health, Science and Technology

New Grafting Technique for Monocots

Scientists have found a novel way to combine two species of grass-like plants — including banana, rice and wheat — using embryonic tissue from their seeds. The technique allows beneficial characteristics, such as disease resistance or stress tolerance, to be added to the plants.

Until now it was thought impossible to graft grass-like plants in the group known as monocotyledons because they lack a specific tissue type, called the vascular cambium, in their stem.

Researchers at the University of Cambridge have discovered that root and shoot tissues taken from the seeds of monocotyledonous grasses — representing their earliest embryonic stages — fuse efficiently. Their results were published in the journal Nature.

An estimated 60,000 plants are monocotyledons; many are crops that are cultivated at enormous scale — for example, rice, wheat and barley.

The finding has implications for the control of serious soil-borne pathogens, including Panama Disease, which has been destroying banana plantations for over 30 years. A recent acceleration in the spread of this disease has prompted fears of global banana shortages.

The technique allows monocotyledons of the same species, and of two different species, to be grafted effectively. Grafting genetically different root and shoot tissues can result in a plant with new traits — ranging from dwarf shoots to pest and disease resistance.

The scientists found that the technique was effective in a range of monocotyledonous crop plants, including pineapple, banana, onion, tequila agave and date palm. This was confirmed through various tests, including the injection of fluorescent dye into the plant roots — from where it was seen to move up the plant and across the graft junction.

According to the lead author of the paper, “Our technique allows us to add disease resistance, or other beneficial properties like salt tolerance, to grass-like plants without resorting to genetic modification or lengthy breeding programs.”

The researchers have filed a patent for their grafting technique through Cambridge Enterprise.

Scientists Solve the Grass Leaf Conundrum

Grass is cut regularly by our mowers and grazed on by cows and sheep, yet it continues to grow back. The secret to its remarkable regenerative powers lies in part in the shape of its leaves; but how that shape arises has been a topic of longstanding debate.

The debate is relevant to staple crops such as wheat, rice and maize, which are all members of the grass family.

The mystery of grass leaf formation has now been unraveled by a John Innes Centre team, in collaboration with Cornell University and the University of California, Berkley, and the University of Edinburgh, using the latest computational modeling and developmental genetic techniques.

Flowering plants can be categorized into monocots and eudicots. Monocots, which include the grass family, have leaves that encircle the stem at their base and have parallel veins throughout. Eudicots, which include brassicas, legumes and most common garden shrubs and trees, have leaves that are held away from the stem by stalks — termed petioles — and typically have broad laminas with net-like veins.

In grasses, the base of the leaf forms a tube-like structure, called the sheath. The sheath allows the plant to increase in height while keeping its growing tip close to the ground, protecting it from the blades of lawnmowers or incisors of herbivores.

In the nineteenth century, botanists proposed that the grass sheath was equivalent to the petiole of eudicot leaves. But this view was challenged in the twentieth century, when plant anatomists noted that petioles have parallel veins, similar to the grass leaf, and concluded that the entire grass leaf (except for a tiny region at its tip) was derived from petiole.

Using recent advances in computational modeling and developmental genetics, the team revisited the problem of grass development. They modeled different hypotheses for how grass leaves grow and tested the predictions of each model against experimental results. To their surprise, they found that the model based on the nineteenth-century idea of sheath-petiole equivalence was much more strongly supported than the current view.

This mirrors findings in animal development where a discarded theory — that the “underbelly” side of insects corresponds to the back of vertebrates like us — was vindicated in the light of fresh developmental genetic research.

The grass study shows how simple modulations of growth rules, based on a common pattern of gene activities, can generate a remarkable diversity of different leaf shapes, without which our gardens and dining tables would be much poorer.

New Understanding of Plant Nutrient Response Could Improve Fertilizer Management Strategies

New work from Carnegie, Michigan State University, and the National Research Institute for Agriculture, Food and Environment in France has revealed the complex, interdependent nutrient responses underpinning a potentially deadly low-chlorophyll state called chlorosis that’s associated with an anemic, yellow appearance. Their findings, published by Nature Communications, could usher in more environmentally friendly agricultural practices — using less fertilizer and fewer water resources.

Photosynthesis is the complex biochemical process by which plant cells convert the sun’s energy into chemical energy, which then is used to fix carbon dioxide from the atmosphere into sugar molecules. It occurs inside highly specialized plant cell organelles called chloroplasts.

Nutrients accumulate in chloroplasts and are essential to their optimal functioning. The research team showed that a balance of both iron and phosphorus are necessary to prevent chlorosis. 

“For a long time, experts have thought that low iron is the sole cause of chlorosis, and farmers have often applied iron to combat leaf yellowing,” a researcher explained. “But recent work has shown that other nutrients play a role in bringing about this anemic reaction.”

To better understand what makes leaves chlorotic, the investigators decided to look at the response to multiple nutrients in concert, rather than one by one.

They found that plants showing chlorosis induced by iron deficiency would yellow and that photosynthetic activity would be affected, as expected. However, when the nutrient phosphorus was also removed, the plant’s leaves started accumulating chlorophyll and turned green again.

The explanation for this unexpected response lies in the signaling between the chloroplast, where photosynthesis occurs, and the cell’s nucleus, where its genetic code is stored.

Interdisciplinary analyses indicated that the nucleus’ ability to regulate gene expression in response to low iron depends on the availability of phosphorus. This kind of complex layering of nutrient responses shows that there is much still to learn about these communication channels between these two crucial plant organelles.

Plant Pathogen Evades Immune System by Targeting the Microbiome

A team of biologists has identified that the pathogenic fungus Verticillium dahliae, responsible for wilt disease in many crops, secretes an “effector” molecule to target the microbiome of plants to promote infection. The research is reported in the Proceedings of the National Academy of Sciences.

Scientists increasingly recognize that an organism’s microbiome — the totality of bacteria and other microbes living in and on it — is an important component of its health. For humans as well as other animals, particular microbes inhabiting the gut and the skin have beneficial effects. This is similarly true for plants. Moreover, it has been established that plants can “recruit” beneficial microbes from their environment — for instance, from the soil surrounding the roots — to help them withstand disease.

The team hypothesized that if plants can do this, perhaps some pathogens have “learned” to perturb this “cry for help” and disturb the plant’s microbiome in order to promote invasion. Thus, in addition to the direct suppression of the plant host’s immune responses, these pathogens can suppress immunity indirectly by affecting the plant’s healthy microbiome.

Verticillium dahliae is a well-known pathogen of many plants, including greenhouse crops like tomatoes and lettuce, but also olive trees, ornamental trees and flowers, cotton, potatoes and others. The current study shows that the fungus secretes the antimicrobial protein VdAMP3 in order to manipulate the plant’s microbiome as an effector.

Generally, effector molecules target components of the host immune system, leading to immune suppression. The authors have now shown that these targets extend to inhabitants of the host’s microbiome: during host colonization, the VdAMP3 molecule suppresses beneficial organisms in the microbiome of the plant, leading to microbiome disturbance or “dysbiosis,” so that the fungus can complete its life cycle and produce progeny that can spread and start new infections.

“Interestingly, the molecule does not act like a broad-spectrum antibiotic that targets any microbe,” one of the researchers remarked, “but specifically against ‘competitor’ fungi that have abilities to hinder Verticillium.

“Together, these findings demonstrate that pathogens use various molecules at various stages of the disease process to manipulate the healthy microbiome of a host to cause disease. This shows that it is important to look beyond the ‘binary interaction’ between a pathogen and a host if we want to understand disease. Rather, we must take the entire microbiome of the host into account as well — looking at the host as a ‘holobiont’ — the ecological unit formed by the host and all the organisms living in and on it.”

How Plants Respond to Heat Stress

To survive short periods of heat stress, plants activate a molecular pathway called the heat-shock response. This heat-shock response (common to all organisms) protects cells from damage inflicted by proteotoxic stress, which damages proteins. Such stress is not only caused by heat but can also result from exposure to certain toxins, UV light or soil salinity.

The heat-shock response protects cells in various ways — one of them being production of so-called heat-shock proteins, which serve as molecular shields that protect proteins by preventing misfolding.

Plants respond to heat stress by activating heat shock factors and also other molecular players. In particular, hormones as chemical messengers are involved. Among the hormones that plants produce are the brassinosteroids, which primarily regulate their growth and developments. But, in addition to their growth-promoting properties, brassinosteroids have other interesting abilities, one of them being their ability to increase the heat stress resistance of plants, and researchers at the Technical University of Munich have recently discovered what contributes to this protective ability.

Using the model plant Arabidopsis thaliana, a research group has been able to elucidate how a specific transcription factor — a special protein responsible for switching certain sections of the DNA on or off — is regulated by brassinosteroids. This transcription factor, called BES1, can interact with heat shock factors, thereby allowing genetic information to be targeted toward increased synthesis of heat shock proteins. When BES1 activity is increased, plants become more resistant to heat stress, and when it is decreased, they become more sensitive to it. Furthermore, the group has demonstrated that BES1 is activated by heat stress and that this activation is stimulated by brassinosteroids.

“These results are not only of interest to biologists trying to expand our understanding of the heat shock response but also have potential for practical application in agriculture and horticulture,” said one of the researchers.

Biostimulants containing brassinosteroids are available and can be tested for their ability to increase heat stress resistance in plants. Such substances are natural products that are approved for organic farming and thus could be used without problems. Alternatively, BES1 may be an interesting target for breeding approaches. This could be used to create varieties that are more resistant to heat stress and thus provide more stable yields in the event of future heat waves.