The discovery of the enzyme responsible for the formation of suberin could lead to easier agricultural production of crops used for biofuels, according to the US Department of Energy. The discovery, made by a team of scientists from the US DOE's Brookhaven National Laboratory, was unveiled this week in an paper in the Proceedings of the National Academy of Sciences.

These images show that seeds deficient in HHT (right), an enzyme needed to synthesize an important component of plant cell walls, are more permeable to a red dye than normal plant seeds (left). Controlling the level of this enzyme may offer scientists a new way to alter plant growth for improved biofuel production.

"We sought to understand the synthesis of the 'wall-bound' phenolic component of different biopolymers, including this important suberin polymer, by identifying the enzymes responsible for their construction," said Chang-Jun Liu on of the team leaders at Brookhaven. "This information could eventually be used to modify plants for agricultural purposes, including improved biomass production. "Knowing which enzymes do what may allow the properties of polymers to be tailored for specific purposes through either plant breeding or genetic engineering," Liu explained.

In this experiment, Liu and colleagues analyzed a strain of Arabidopsis (a common experimental plant) that had been genetically modified to disrupt the expression of a gene that codes for an enzyme now known as hydroxyacid hydroxycinnamoyltransferase (HHT). Chemical analysis showed that "knocking out" the HHT gene led to a deficiency of suberin phenolics, indicating that HHT is the enzyme responsible for biosynthesis of the polymer. Liu and his colleagues then isolated the gene and expressed it in bacteria to further characterize its function.

The team also demonstrated that the HHT-deficient plants were much more permeable to salt in solution than their wild-type counterparts. This finding, together with the ubiquitous presence of suberin in plant root tissues that control water and salt uptake, suggests that suberin plays an important role in the adaptation of plants to their terrestrial habitats.

Harnessing the mechanism responsible for suberin production might therefore allow scientists to create crop breeds tailored to thrive in specific — even harsh — environments, an important milestone on the road toward economically efficient biofuel production.

"Identifying the key biosynthetic enzymes and understanding suberin production may be particularly important for growing plants on the marginal soils that have been proposed for use in farming bioenergy crops," Liu said.

For example, if certain breeds can be created that are more adept at absorbing and storing water and nutrients, the crops could be farmed in much drier climates — maybe even the desert. In addition, the team’s finding that modifications in suberin phenolic production can alter plants’ tolerance to salt suggests that the newly-identified gene might be used to generate crops able to grow under salty conditions.

This research was funded by the DOE-United States Department of Agriculture Plant Feedstock Genomics program and by DOE’s Office of Science.