Duckweed has been modified by researchers at Cold Spring Harbor Laboratory (CSHL) and Brookhaven National Laboratory, both of the U.S. Department of Energy. In order to “push” the production of fatty acids, “pull” those fatty acids into oils, and “guard” the oil from deterioration, the scientists introduced genes to one of nature’s fastest-growing aquatic plants. Such oil-rich duckweed might be easily gathered to make biofuels or other bioproducts, the researchers write in a report that was published in Plant Biotechnology Journal.
As described in the research, Lemna japonica, a type of duckweed, was modified by scientists to accumulate oil at a rate that is close to 10% of its dry weight biomass. With yields more than seven times higher than soybeans, the current leading source of biodiesel, it is a striking 100-fold improvement over similar plants growing in the wild.
Duckweed grows quickly, according to the team’s leader, scientist John Shanklin of Brookhaven Lab.The majority of its biomass is found in leaf-like fronds that grow on the surface of ponds all over the world since it only has minuscule stems and roots. All that biomass has a significant oil content thanks to our engineering.
He said that growing and harvesting this changed duckweed in batches and getting the oil from it would be a good way to make oil that can be used again and again.
Two further advantages: Oil-producing duckweed wouldn’t compete with food crops for valuable agricultural land because it is an aquatic plant. Even farm runoff from pig and chicken farms can support its growth.
So, Shanklin said, “this building might be able to clean up streams of agricultural waste while it makes oil.”
Using two research institutions on Long Island,
The 1970s research on duckweeds conducted by William S. Hillman in the Biology Department at Brookhaven Lab served as the foundation for the current undertaking. Later, other faculty members from the Biology Department collaborated with the Martienssen group at Cold Spring Harbor to create a highly effective technique for expressing genes from other species in duckweeds, as well as strategies to block the production of the duckweeds’ own genes as needed.
One objective was to use this information and the genetic tools to try to manipulate plant oil production as Brookhaven researchers led by Shanklin and Jorg Schwender over the past two decades identified the major biochemical processes that drive oil synthesis and accumulation in plants. The most recent work, which is described here, looked into this strategy by putting the genes that control these oil-making parts into duckweed so that their combined effects could be studied.
According to Shanklin, the current effort combines Cold Spring Harbor’s cutting-edge genomics and genetics skills with Brookhaven Lab’s expertise in the biochemistry and regulation of plant oil production.
The Brookhaven scientists discovered a gene that promotes the creation of fatty acids, which are the fundamental components of oil. One more gathers, or assembles, those fatty acids into triacylglycerols (TAG), which are combinations of three fatty acids that combine to form the hydrocarbons we refer to as oils. A protein made by the third gene covers oil droplets in plant tissues to prevent them from degrading.
Based on early research, the researchers discovered that the “push” gene’s increased fatty acid levels can be harmful to plant growth. Yuanxue Liang, a postdoctoral researcher at Brookhaven Lab, linked that gene with a promoter that may be activated by the injection of a small quantity of a certain chemical inducer to avoid such consequences.
According to Shanklin, this promoter keeps the push gene switched off until the inducer is added, allowing the plants to grow normally until fatty acid or oil synthesis is turned on.
The improved push, pull, and protect factors were then expressed singly, in pairs, or all at once using a range of gene combinations that Liang designed. The biochemical/genetic names of these are shortened in the paper as W, D, and O, where W stands for push, D for pull, and O for protection.
The main conclusions
The amounts of fatty acids in Lemna japonica fronds were not considerably raised by the overexpression of any one gene modification. When data from multiple distinct transgenic lines were averaged, plants with all three alterations accumulated up to 16 percent of their dry weight in fatty acids and 8.7 percent in oil.The finest plants produce up to 10% TAG, which is more than 100 times the amount of oil produced by unaltered wild type plants.
In comparison to their separate effects, several combinations of the two changes (WD and DO) greatly enhanced fatty acid content and TAG accumulation. When two genes work together to raise production more than the total effect of the two individual changes, this is called a synergistic effect.
These findings were further supported by confocal microscopy photographs of lipid droplets in the plant fronds at the Center for Functional Nanomaterials (CFN), a DOE Office of Science user facility at Brookhaven Lab. The photos revealed that plants with each two-gene combination (OD, OW, and WD) had a greater accumulation of lipid droplets relative to plants where these genes were expressed singly as well as when compared to control plants with no genetic change. Large oil droplets were present in plants from both the OD and OWD lines, but the OWD line had more of them, resulting in the greatest signals.
According to Shanklin, future research will concentrate on examining push, pull, and protect factors from a number of different sources, as well as on maximizing the quantities and timing of the expression of the three genes that cause the production of oil. In addition, we are figuring out how to increase manufacturing from laboratory to industrial levels.
There are several key goals of the scale-up work:
- developing various large-scale culture vessels for transgenic plant cultivation,
- Improving the environment for large-scale growth, and
- developing effective high-level oil extraction strategies
The Office of Science at DOE provided funding for this project (BER). The Office of Science provides assistance to CFN as well (BES).
