New genetic strategy to prevent degradation of plant oils needed for biofuels and other products

Biologists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have demonstrated a new way to increase the oil content of plant leaves and seeds. As described in the newspaper New plant scientist, scientists have successfully identified and modified key parts of a protein that protects newly synthesized oil droplets. The genetic alterations essentially protect the oil’s protective protein so that more oil can accumulate.

“Implementing this strategy in bioenergy or oilseed plants could help meet the growing demand for biodiesel fuel and/or nutritionally important vegetable oils,” said Brookhaven Lab biochemist John Shanklin, chair of the Department of laboratory biology, who led the research.

Shanklin’s team has worked for years to stimulate the accumulation of plant oil, particularly in parts of plants such as leaves that typically don’t produce much oil. These vegetative tissues generally represent the majority of plant biomass.

Increasing their ability to accumulate oil would significantly increase the energy content of biomass. And since vegetable oils are essential raw materials for making biodiesel, the strategy could transform cultivated plants into green factories to produce sustainable fuels.

Push, pull, protect

Much of the Brookhaven team focused on implementing genetic strategies that biochemically nudge plant cells to produce more oil and store that newly synthesized oil in lipid droplets, rather than processing it. into new plant parts.

“But once oil is made, it can be broken down, and the level of accumulation is the balance between synthesis and degradation,” Shanklin explained.

So the scientists also used a third approach: increasing the production of proteins that protect lipid droplets from degradation.

One of these protective proteins produced naturally by plants is known as oleosin. Oleosin embeds itself in the membrane of oil droplets, blocking access to enzymes called lipases that trigger oil breakdown.

“We and others generally increase the levels of this small protein to protect lipid droplets,” Shanklin said.

But oleosin itself can be degraded, limiting its effectiveness. So in the new work, Shanklin and his team looked for a way to protect the oil protectant.

“This was a complex puzzle that the lead author, Sanket Anokar, worked creatively to solve,” Shanklin said. Anokar is a research associate at Brookhaven Lab in the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), a bioenergy research center led by the University of Illinois at Urbana-Champaign.

Removal of degradation signals

“We thought that if we could identify and remove the parts of oleosin recognized by degrading enzymes – the degradation ‘signals’ – we could make the oleosin stay and enhance oil accumulation,” Anokar said.

Using clues from other groups that had used a different approach to solving this problem, the scientists designed variants of the oleosin protein and tested their effects on tobacco leaves.

The team initially designed the variants to change all the amino acids thought to be involved in oleosin degradation. Then they reversed the mutations one by one and looked for the largest changes in oil accumulation. Ultimately, this allowed them to identify a few key mutations that made oleosin significantly more resistant to degradation.

“These changes caused the oleosin variants to accumulate at higher levels, which in turn protected the oil more effectively, so the oil levels also increased,” Shanklin said.

Plants expressing the most successful mix of genetic modifications accumulated 54% more oil in their leaves and 13% more in their seeds compared to unmodified plants.

Chance surprise

A surprising finding was that modifications to protect the oil droplets did not have negative effects on plant growth or the ability of seeds to germinate. This was surprising because plant seeds must break down stored oil to fuel germination and early stages of seedling growth, that is, until the plant has established itself and developed sufficient leaves. so that photosynthesis can start and fuel its further growth.

“We were initially concerned that preventing oil degradation during seed development would inhibit this establishment process,” Shanklin said. “But we found that establishment is not affected by the oleosin variants. This tells us that, early in its growth, the plant uses another mechanism to break down the oil so that seedlings can access its stored energy.

“We don’t yet know what this process is, but it allows us to use oleosin variants to increase oil accumulation in vegetative tissues and seeds without harming seedling growth,” Shanklin said. .