Researchers, trying to uncover the details of how plants produce and accumulate oil within them, have managed to identify a new essential component in this mechanism. They found a certain sterol - a molecule similar in its structure to cholesterol - that plays an essential role in the formation of oil droplets
[Translation by Dr. Moshe Nachmani]
![Creation of an oil droplet: oil (in yellow) accumulates between the layers of the membrane that forms the 'cellular plasma retina' (ER). The droplets grow and eventually detach and become part of the cytoplasm. This process occurs only in microcomplexes rich in sterols and oleosins along the membrane. [Courtesy of Brookhaven National Laboratory]](https://www.hayadan.org.il/images/content3/2021/09/Lipid-Droplet-Formation-on-Endoplasmic-Reticulum1.png.webp)
"This research significantly expands our understanding of the molecular factors that control the creation of lipid droplets, which are essential organelles for oil storage, and their metabolism in all eukaryotic organisms (from Wikipedia: cellular organisms with a nucleus and organelles, which constitute a superkingdom in the order of the natural world. They include a variety a large number of organisms, including single-celled protozoa, mucous membranes, algae and single-celled fungi, as well as the multicellular kingdoms: fungi, plants and animals (including humans)," said lead researcher Changcheng Xu from the US Department of Energy's National Laboratory "B. The new findings, which were published as part of an article in the scientific journal Nature Communications., may provide new methods for engineering the oil content in a variety of plants.
The research may be particularly important for the development of genetic engineering methods aimed at increasing the oil content in leaves and other plant parts. These parts of the plant usually do not contain oil, but with the help of the new findings it will be possible to engineer them so that they will be used as a common source of sustainable oils that are starting materials for the preparation of biofuels and other commercial products, the researchers explain. The findings are also important in the field of oil content in seeds, the main source of plants in nature where they store their oil. These natural reservoirs of vegetable oils provide the nutrients for the sprouts and seedlings of the plants - as well as for animals and humans. "We found that the omission of a certain type of sterol causes a decrease in the accumulation of oil in seeds and leaves," explains the lead researcher, who and his research group have been working for years with the aim of increasing the oil content in plant parts.
"Leaves, compared to seeds, are much more common as a possibility for bioenergetic material," he explains. "In addition, since the oil found in the seeds is used for food, our goal is to increase the oil content in the parts of the plant that are not seeds, for example leaves and stems, for the production of commercial products, and thereby avoid competition between their use as food and their use as fuel."
The research team achieved success in engineering leaves so that they accumulate a significant amount of oil inside them, using the common laboratory plant Arabidopsis. The researchers developed a simple and effective method to measure the oil content - with the help of genetic engineering, they created plants in which a green glowing protein is permanently bound to a protein called oleosin. This protein accumulates exclusively on the outer surface of the lipid droplets and is part of the membrane that envelops organelles that store oil inside the cells, this is to assist in their structural stabilization. If a sample of plant tissue - leaf, stem or seed - contains oil droplets it will stand out as a small green dot under a careful microscope. "We treated our plants with a mutagen in order to cause changes that would increase the accumulation of oil," said the chief researcher. "The main goal of our research was to find those genetic changes that would lead to a significant increase in the oil content in the various plant parts, while finding new genes or proteins that are important in the mechanism of the production of oil droplets or their accumulation."
At the microscopic level, scientists know that lipid droplets are formed inside cell organelles called the endoplasmic reticulum. These organelles form an internal network of membranes inside the cells (not the main membrane that envelops the entire cell) that serve as a type of factory that produces a variety of substances such as proteins and lipids.
Lipid droplets used for storage are formed when the oil begins to accumulate between two layers of the 'cellular plasma retinal' membrane, but only in those certain areas there. Eventually, when there is enough oil, the small membrane is detached leaving the drop of oil stored inside dedicated enclosures.
In order to find those mutations that cause an increase in the accumulated oil content, the research team used a method known as 'positional cloning' - a method in which each and every part of the chromosomes is searched while identifying specific genes responsible for this mechanism. As part of this method, the part that is being searched is reduced in order to find those important genes, even though these areas still contain hundreds of possible genes", explains the lead researcher. After complete genetic sequencing of this part, the research team identified a gene suspected to be involved in the mechanism. This gene encodes an enzyme responsible for a certain biochemical step in the multi-step synthesis of sterol, a molecule structurally similar to cholesterol and which is found in the various cell membranes. By 'knocking out' the original (non-mutant) version of this gene, the scientists were able to replicate the effect of the mutation. That is, plants containing this cloned gene did not accumulate any lipid droplets, while the introduction of the original gene restored the oil accumulation. "This experiment provided conclusive proof that sterol plays a necessary role in the formation of oil droplets," explains the lead researcher.
However, the scientists went a step further - they investigated what happens when the genes encoding other enzymes involved in the multi-step synthesis of sterol are changed while measuring the sterol content in each case. The detailed experiments allowed the researchers to find the specific type of sterol whose absence causes a reduction in fat accumulation. "We believe that this sterol is essential for the formation of micro-complexes in the membrane involved in the creation of lipid droplets," explains the lead researcher. "The absence of this sterol causes a disruption in the production mechanism of these micro-complexes".
The full article about the study
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