Scientists have discovered that sterols are necessary for the accumulation of oil in plants

Scientists trying to unravel the details of how plants produce and accumulate oil have identified a new important part of the assembly line

"This research greatly expands our understanding of the molecular factors that control the formation of lipid droplets, which are important organelles for all eukaryotic organisms to store and metabolize petroleum," said Changcheng, a biologist at Brookhaven National Laboratory, U.

This work may have particular significance for genetic engineering strategies to increase oil content in leaves and stems

These findings also apply to the accumulation of oil in plant seeds, which is the main place where oil naturally accumulates in plants

Professor Xu said: "We found that the lack of a special type of sterol can lead to a decrease in the accumulation of oil in seeds and leaves

Green light for oil production

Xu and his team have been working on increasing the accumulation of oil in plant leaves and stems for many years

"As a possible bioenergy material, leaves are much richer than seeds," he pointed out

The team used the common plant Arabidopsis thaliana in the laboratory to make some progress in allowing the leaves to accumulate large amounts of oil

They invented an easy way to track oil accumulation

"We treated Arabidopsis with mutagens to try to trigger mutations and increase oil accumulation," Xu said, using fluorescence technology to identify strains with more and/or larger green spots

Ironically, they found sterols in an Arabidopsis strain that hardly accumulates oil

"The main purpose of the current work is to find out what kind of genetic modification caused the sharp drop in oil accumulation," Xu said

Clues to internal assembly

Under the microscope, scientists know that lipid droplets are formed in the cell's "endoplasmic reticulum" or ER

When oil begins to accumulate between the two membranes of the endoplasmic reticulum, lipid storage droplets are formed, but only in certain areas of the endoplasmic reticulum

As Brookhaven’s research shows, studying a plant that does not accumulate these lipid droplets can provide clues to the biochemical factors driving this process and the uniqueness of the specific endoplasmic reticulum domain where lipid droplets occur
.

Target gene

In order to figure out which mutation caused the sharp drop in oil accumulation, Brookhaven’s research team used a technique called positional cloning—a method of searching every region of a chromosome to identify a specific one.
Gene, the gene is responsible for a characteristic of interest
.
This technology narrows the search to a specific area of ​​a plant chromosome
.

"This region still contains hundreds of candidate genes," Xu said
.

After using whole-genome sequencing to look for any mutations in the region, the research team identified a gene they suspected to be related to
.
This gene encodes an enzyme that is responsible for a biochemical step in the multi-step synthesis process of sterols, a cholesterol-related molecule found in the endoplasmic reticulum and other cell membranes
.

By selectively "knocking out" the normal (unmutated) version of the gene, scientists can replicate the effects of the mutation
.
In other words, plants whose genes have been knocked out do not accumulate lipid droplets
.
In addition, the addition of unmutated genes restored the accumulation of oil droplets
.

Xu said: "This experiment provides clear evidence that sterols play a vital role in the formation of oil droplets
.
"

But scientists go further
.
They also studied what happens if the gene of the enzyme is mutated "upstream" of this specific enzyme in the multi-step sterol synthesis pathway
.
They measured the sterol levels of these mutants
.

Detailed research has allowed them to target specific types of sterols, which when lacking, lead to low oil accumulation
.

Mutations in the same gene lead to reduced oil accumulation in leaves and seeds
.
Among the seeds where lipid droplets are easier to see, scientists have also conducted quantitative studies on their shape and size
.

These results provide evidence for the universal role of this particular sterol in lipid droplet formation
.

Professor Xu said: "We believe that this kind of sterol is essential for the formation of endoplasmic reticulum membrane microdomains, and the microdomains are involved in the formation of lipid droplets
.
" The lack of sterols leads to defects in the formation of such microdomains
.

Now that scientists know what happens when these genes are turned off, they think the strategy of turning on these genes and increasing their expression may be a way to increase the accumulation of oil in leaves, stems or seeds
.

DOI

10.
1038 / s41467-021-25908-6

During seed development, the coordinated assembly of lipid droplets requires sterols