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Researchers reveal new strategy for biofuels from straw

A collaborative research effort by researchers at the University of Hong Kong (HKU) and Kyoto University (Kyoto U) in Japan has revealed a new strategy to allow cellulose in rice straw to release its fermentable sugar more efficiently.

Dr Lydia Lam Pui-ying (left) and Dr Clive Lo Sze-chung (photo courtesy HKU).

With an increasing demand for biofuel in recent years, cellulose from non-edible plant materials such as sugarcane leaves, corn stalks and rice straw has been used as raw materials for ethanol production. However, since cellulose is crosslinked with lignin in plant cell walls, it is very difficult to release the fermentable glucose from cellulose.

Lignin is a complex polymer which functions to provide mechanical strength and structural integrity in plants and expensive and complicated procedures are required to loosen the lignin barrier in order to utilize cellulose more efficiently during the production of ethanol.

A collaborative research effort by the University of Hong Kong (HKU) and Kyoto University (Kyoto U) in Japan has revealed a new strategy to allow cellulose in rice straw to release its fermentable sugar more efficiently. The research breakthrough has been published in an article “Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility” in a recent issue of the journal Plant Physiology.

Reducing lignin formation

Rice and other cereals belong to the grass family (Poaceae). Lignin in their stems and leaves contain a special component called tricin. HKU plant biochemists Dr Clive Lo Sze-chung and his student Dr Lydia Lam Pui-ying, together with Kyoto U lignin specialist Dr Yuki Tobimatsu, started a collaborative project two years ago.

According to their discovery, when flavone synthase II (FNSII), a key enzyme involved in tricin synthesis, is knocked out, not only is tricin not produced, but the lignin content in rice straw was also reduced by approximately one-third.

In addition, the yield of glucose from cellulose degradation was increased by 37 percent without any chemical treatment. The glucose released from cellulose can be used for ethanol production. In other words, it is more efficient to produce ethanol from this kind of rice straw: the cost of lignin treatment can be reduced and the production of ethanol can be enhanced.

This is the first demonstration of the reduction of cell wall lignin content in rice straw by the disruption of tricin production. Importantly, there are no negative impacts on rice growth and productivity, said Dr Sze-chung.

As plants in the grass family all contain tricin-bound lignin, this strategy can be applied to other cereals like maize, wheat, and barley as well as grass species such as sorghum and switchgrass cultivated around the world exclusively for ethanol production, so that they can be utilized more efficiently as raw materials for biofuel.

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