‘Fattening-up’ plant leaves for biofuel production

Scientists in the US have discovered that plant leaves retaining sugars ‘get fat’, something which could increase their biofuel and biochemical potential.

The team from the US Department of Energy’s Brookhaven National Laboratory have worked to turn this fat accumulation into higher oil production in the leaves. With leaves more abundant and accessible than seeds, this could simplify the production of biofuels.

"Plants make their own food," said John Shanklin, the Brookhaven Lab biochemist who led the research. "They convert sunlight, water, and carbon dioxide into sugars through photosynthesis, and those sugars are usually transported out of leaves to other parts of the plant, and converted to other compounds plants need for growth and development. Oils tend not to accumulate to high levels, except in some seeds."

The Brookhaven team selectively bred plants to combine a series of traits that blocked some of the sugar transport and conversion pathways, resulting in increased oil production and accumulation.

Based on earlier research, the scientists suspected that keeping more sugar in leaves would increase oil production in those vegetative tissues. The team identified how high sugar levels inhibit a regulatory protein that plays a key role in the breakdown of another protein that serves as a switch for turning on oil-production genes. In the latest study, the scientists found increased levels of the on-switch protein along with higher levels of oil precursors and oil.

“Combining genetic mutations that decrease the transport of sugar out of leaves and the conversion of sugars to starch increases sugar levels in leaves,” Shanklin said. “That excess sugar drives increased oil production by stabilizing the oil on-switch, and also by supplying the carbon building blocks needed to make more oil in leaves.”

According to a statement from Brookhaven, the scientists also bred plants that combined the sugar increasing traits with other mutations, including one that limited the breakdown of plant lipids, resulting in further increases in oil precursor accumulation in leaves.

“In several cases, combinations of these mutations helped tip plant metabolism to produce and store more oil than expected in leaves,” Shanklin said.

“Findings from these foundational biochemical-genetic studies provide valuable insights into the relationship between sugar, oil precursors, and oil accumulation in leaves that will help inform biotechnological efforts to optimize oil accumulation in vegetative tissues of economically important plants.”

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