Scientists at the
"If we can transfer this strategy to crop plants being used to generate renewable energy or to feed livestock, it would significantly increase their energy content and nutritional values," said Brookhaven biochemist
Think about it in the familiar terms of calories: Oil is twice as energy-dense as carbohydrates, which make up the bulk of leaves, stems, and other vegetative plant matter. "If you want to cut calories from your diet, you cut fat and oils. Conversely, if you want to increase the caloric output of your biofuel or feed for livestock, you want more oil," said Xu.
But plants don't normally store much oil in their leaves and other vegetative tissues. In nature, oil storage is the job of seeds, where the energy-dense compounds provide nourishment for developing plant embryos. The idea behind Xu's studies was to find a way to "reprogram" plants to store oil in their more abundant forms of biomass.
The first step was to identify the genes responsible for oil production in vegetative plant tissues. Though oil isn't stored in these tissues, almost all plant cells have the capacity to make oil. But until these studies, the pathway for oil biosynthesis in leaves was unknown.
"Many people assumed it was similar to what happens in seeds, but we tried to look also at different genes and enzymes," said Xu.
Unraveling the genes
The scientists used a series of genetic tricks to test the effects of overexpressing or disabling genes that enable cells to make certain enzymes involved in oil production. Pumping up the factors that normally increase oil production in seeds had no effect on oil production in leaves, and one of these, when overexpressed in leaves, caused growth and developmental problems in the plants. Altering the expression of a different oil-producing enzyme, however, had dramatic effects on leaf oil production.
"If you knock out (disable) the gene for an enzyme known as PDAT, it doesn't affect oil synthesis in seeds or cause any problems to plants, but it dramatically decreases oil production and accumulation in leaves," Xu said. In contrast, overexpressing the gene for PDAT--that is, getting cells to make more of this enzyme--resulted in a 60-fold increase in leaf oil production.
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