A new type of power plants to combat climate change

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The prestigious organization EMBO recently announced several new members, including the appointment of VIB-UGent scientist Prof Wout Boerjan. Boerjan joins over 1800 other EMBO members in what is regarded as one of the top honors for European scientists. The appointment is well deserved, with Boerjan’s research focused on the vital task of building a circular bio-economy by valorizing plants.

By Amy LeBlanc

Most people are familiar with the feeling of a warm log fire, but have you ever considered wood being used as a more high-tech fuel? There are many ways to valorize plant parts, including for fuel, feed, pulp and even plastics. Unfortunately, we are currently only using plant biomass for a fraction of its possible industrial applications. The reasons why are complex, linked to both processing problems and societal issues like our preference for fossil fuels and public disdain for GM plants. Overcoming these challenges is the basis of Wout Boerjan’s research at the VIB-UGent Center for Plant Systems Biology:

“We need a transition from a fossil-based to a bio-based economy,” Boerjan stated in an interview with BioVox. “That is the main focus of my research. Instead of using fossil resources, that release carbon dioxide into the atmosphere and result in climate change, we can use plants for many of the same applications.”

One of the main non-food substances being derived from plants is biofuels like ethanol. These are however just the ‘tip of the tree’ for the potential uses of plant materials: plants can also be converted into a range of products that are currently made using petroleum, such as bio-plastics and detergents. Plant biomass can also be broken down into aromatic molecules that serve as building blocks for the chemical industry. Most plant components can be valorized. And the cherry on top? Plants are essentially the opposite of people, absorbing CO2 from the atmosphere and emitting oxygen, so by growing vegetation, we would be helping to counter the carbon emissions that are currently driving climate change.

Fuel for progress

Breaking down plant biomass into valuable materials is conceptually a relatively simple process. For biofuel, for example, the cellulose in the plant cells is broken down into glucose, using enzymes, which is then converted into ethanol by fermentation. This bioethanol can then be used to power anything from car engines to industrial machines. Creating biofuel out of plant products is already being done with plants like maize. There are several drawbacks to the current process though: nowadays mostly the easily accessible starch (also a polymer of glucose) in corn kernels is being used, with the lignocellulose of leaves and stems going to waste, and growing vast swathes of maize fields for biofuel eats up arable land that could otherwise be used for food production.

It is my hope that, as society becomes more environmentally conscious, we could start converting land currently used for the cattle industry into forests. – Wout Boerjan, VIB-UGent

Because of these disadvantages, researchers have been looking into alternative sources of biofuel fodder. Boerjan has settled on fast-growing trees and is using poplars as the model organism. His selection is backed by a number of specific advantages: poplar has been used as a model plant organism for some time and its genome has been extensively sequenced. The plant is fast-growing and can be clonally propagated by cuttings, so you don’t risk losing the right genes through random recombination during sexual reproduction.

Furthermore, given that trees are perennial plants, they don’t need to be planted and harvested every year, which saves a lot of energy to cultivate them in comparison with e.g. maize. Finally, the plant can be grown in soils not considered suitable for food production, meaning it won’t be vying with food crops for valuable fertile land. Boerjan stated:

“It is my hope that, as society becomes more environmentally conscious, we could start converting land currently used for the cattle industry into forests. And I’m not thinking monocultures of endless neat rows of trees: with a bit of foresight, we could set these production plants up as mosaic ecosystems, with purpose-grown biorefinery trees alternating with patches of native flora and fauna.”

The problem with woody stems

The benefits of using plants in place of fossil-fuels seem overwhelming. So, we have to ask ourselves: why are we not already using trees like this on an industrial scale? The answer is multifaceted but has until recently been rooted in a simple problem: trees are simply too tough.

Tree stems are composed of three primary components: cellulose, hemicellulose and lignin. The cellulose and hemicellulose can be broken down into simple sugars for further fermentation. Lignin is a phenolic polymer that provides strength to the plant: it is what makes wood “woody”. However, when trying to convert plant biomass into the useful simple sugars, the lignin acts as a physical barrier, preventing enzymes from doing their job. Therefore, the substance has to be removed or degraded before the cellulose and hemicellulose can be used.

Traditionally, this lignin removal has been done using high temperatures and chemicals, methods that counteract the environmental benefits of using plants in the first place. But where there’s a will, there’s a way: Boerjan’s lab has been working to solve the lignin challenge and has made some astounding breakthroughs.

I’m quite positive we will be seeing trees, like these low-lignin poplars, planted and used on a large scale in industry relatively soon. – Wout Boerjan, VIB-UGent

A tailor-made solution

Boerjan’s lab at VIB has been trying to solve the lignin problem for a long time. Using genetic modification, the team figured out how to reduce the percentage of lignin in poplar plants quite a while ago: by 2014, the poplar trees in Boerjan’s lab were down from the normal 20% lignin to only 16%. However, the team quickly realized that the reduction came with intolerable side effects:

“This 20% reduction of plant lignin would greatly improve the biorefinery process,” Boerjan says, “but by reducing the overall lignin in the plant, the structural integrity of the plant stems was compromised. The plants were much smaller. So, we were forced to think more creatively about our approach to lignin reduction.”

A real breakthrough came following the lab’s discovery of a new gene involved in lignin production that had been overlooked for decades. Knocking-out the gene’s function in the small model plant Arabidopsis (thale cress) increased the efficiency of cellulose-to-glucose conversion by an astonishing 400%. Reducing the gene’s activity in poplar reduced lignin content by 25% and increased the cellulose-to-glucose conversion by more than 50%, without any effect on the overall growth. Boerjan’s group is now exploring the use of CRISPR-Cas to further reduce lignin content and increase the biomass processing efficiency. Boerjan explains:

“The possibility to reduce lignin is an important step forward towards the usability of plant biomass. The productive, low-lignin plants that our lab has engineered provide a clear advantage over the high-lignin plants currently being grown for use in pulp, paper and biofuel production. It could even be used to make animal feed more digestible. The potential benefits are enormous.”

This genetic modification has given the plants the edge needed to become an effective resource for a circular economy. So why are these trees not already being planted and harvested?

We’ll need to use all the breeding tools we have, including GM and CRISPR-Cas, to be able to feed carbon-neutral biomass instead of oil into the economy, before the climate crashes. – Wout Boerjan, VIB-UGent

A change is needed

Research and clever problem solving has provided us with plants engineered to better suit our needs. But we have yet to see a single low-lignin forest planted. Unfortunately, in today’s climate of GM skepticism, not many companies are incentivized to invest in this new technology. With our current restrictive GM regulations in Europe, the trees cannot be grown for industrial harvesting in Europe. However, even in nations with more progressive GM regulations, like the US, low-lignin trees have not yet been commercialized due to the expensive regulatory burden.

“Companies are still hesitant to invest in GM trees,” Boerjan told us. “Their current stance is that the market isn’t ready; public opinion towards GM plants, whether for food or fuel, is still perceived to be too negative. The fact is, even if there is a very strong environmental benefit to using plant-based biofuels and products, fossil fuels and conventional plastics are still a cheaper alternative. The societal pressure to move away from them and towards sustainable resources isn’t yet in full force.”

Click here to read more about CRISPR crop regulations in the EU.

Yet fossil fuels are doomed to burn out. The pressure to move towards a sustainable bio-based economy will rise. If the benefits of using carbon-neutral GM plants becomes clear to the general public, companies will start to invest. And when GM plants are deemed more marketable, the low-lignin plants will be there, ready to flourish. Boerjan is hopeful:

“I’m quite positive we will be seeing trees, like these low-lignin poplars, planted and used on a large scale in industry relatively soon. The biggest problem the world faces today is climate change, caused in large part by unsustainable agriculture and fossil fuels. We have to find new solutions to our current linear economy and necessity will drive change. We’ll need to use all the breeding tools we have, including GM and CRISPR-Cas, to be able to feed carbon-neutral biomass instead of oil into the economy, before the climate crashes.”