Gene discovery could create denser biomass

By Luke Geiver | January 06, 2011

A new gene discovery made by a team of plant research scientists at The Samuel Roberts Noble Foundation “clearly looks like a way of essentially producing more biomass and giving a greater source of fermentable sugar per acre,” according to lead researcher, Richard Dixon, director of the Noble Foundation’s Plant Biology Division. The gene discovery, which can be attributed to an initial interest in devising methods to improve forage quality in alfalfa, was found after the team began analyzing mutated alfalfa plants that had altered patterns of lignin deposition.

“We were looking through these plants at cross sections in the stem,” Dixon said. “In the normal alfalfa plant, the lignin is present in a ring that is fairly close to the circumference of the stem, but we noticed that in some of the plants, the lignin appeared to be present throughout the whole of the stem, so it filled up that whole central part of the stem,” called the pith. Normally, Dixon noted, plant cell walls in the pith are thin and don’t contain much material, but these plants contained not only additional lignin, but also increased amounts of celluloses and hemicelluloses. “When we actually looked at the dry matter density of the stem, it was increased by 50 percent, which is a huge amount.”

The team had an alfalfa plant in which a gene had been knocked out, and that was causing the increase in cell wall material throughout the stem, Dixon explained. The method the team used to knock out the gene was relatively simple, he said, and the team decided to look at another readily researched plant, Arabidopsis, and test their findings. “What was really exciting was that once we thought we knew what the gene was and we looked at Arabidopsis and obtained plants in which the gene was knocked out, the plants had exactly the same appearance with the stem,” he said.

The gene the research team was working with is known as a worky transcription factor. “Transcription factors are ‘master switches,’” Dixon said. The importance of the gene, or recognizing the gene’s presence as a master switch, has to do with what we know about lignin, cellulose and hemicelluloses, he said. The Noble Foundation’s work shows that it is possible, by knocking out a single gene, to increase the amount of lignin, cellulose and hemicellose in a plant, he said. We understand a lot about how lignin is made in the plant (it takes about 15 to 20 steps) but, in the case of cellulose, “nobody has been able to increase cellulose by playing around with the cellulose-making machinery of the plant, because we don’t understand it,” Dixon said. By targeting a master switch that basically sends a single message to a plant to do its thing, he explained, everything is turned on within the plant, or off in this case, “even if we don’t understand the exact mechanism by which the cellulose is being made.”

Researchers have long thought that over-expressing the genes that make cellulose would help to make it, but that has never really worked, he said. It’s similar to electricity—one doesn’t have to “understand” electricity to turn on the lights.

While the team feels confident in its findings, the next question is whether it will work with grasses such as switchgrass, Dixon said. Although the structure of the switchgrass stem is a bit different from alfalfa, “it looks as though switchgrass does contain equivalent genes” and the team is in process of starting research. If switchgrass genes are similar to alfalfa genes, and the manipulation works, not only will the work create a larger amount of fermentable cell wall material, but it will require fewer trips to transport the high-density biomass, Dixon said.

So far, there have been no negative effects, which the team initially thought it might find, from the added biomass in the plant.

This article first appeared in Biorefining Magazine.