Scientists have created a yellow-seeded gorse with a high oil content

Efforts to achieve net zero carbon emissions from fuels are increasing demand for oil produced from non-food crops. These plants use sunlight to convert atmospheric carbon dioxide into oil, which is stored in the seeds. Crop breeders interested in selecting plants that produce a lot of oil look for yellow seeds. In oil crops such as canola, yellow-seeded varieties generally produce more oil than their brown-seeded counterparts. The reason: The protein responsible for the brown color of the seeds – which yellow-seeded plants lack – also plays a key role in oil production.

Plant biochemists at the US Department of Energy’s (DOE) Brookhaven National Laboratory, interested in enhancing the synthesis of plant oils for the sustainable production of biofuels and other bioproducts, have used this knowledge to create a new high-yielding oilseed variety. In the newspaper just published in The Plant Biotechnology Journaldescribe how they used the tools of modern genetics to produce a yellow-seeded variety of Camelina sativa, a close relative of canola, that accumulates 21.4% more oil than the common camelina.

“If breeders can get a few percent increase in oil production, they see that as significant, because even a small increase in yield can lead to a big increase in oil production when you’re planting millions of acres,” said Brookhaven Lab biochemist John Shanklin. chairman of the laboratory’s biology department and head of the vegetable oil research program. “Our nearly 22% increase was unexpected and could potentially lead to a dramatic increase in production,” he said.

Straightforward idea, unusual plant

The idea behind the development of this high-yielding camelina strain was straightforward: to mimic what happens in naturally occurring high-yielding canola varieties with yellow seeds.

“Breeders identified plants with more oil, some of which happened to have yellow seeds, and they didn’t really care about the mechanism,” Shanklin said. But once scientists discovered the gene responsible for the yellow seed color and increased oil content, they had a way to potentially increase oil yield in other species.

The gene has instructions for making a protein known as Transparent Testa 8 (TT8), which, among other things, controls the production of compounds that give seeds their brown color. Importantly, TT8 also inhibits some genes involved in oil synthesis.

Xiao-Hong Yu, who led the project, hypothesized that removing TT8 in camelina should release the inhibition of oil synthesis—and free up some carbon that can be channeled into oil production.

Getting rid of a single gene in a line is very challenging because this plant is unusual among living things. Instead of two sets of chromosomes—that is, two copies of each gene—it has six sets.

“This ‘hexaploid’ genome explains why there are no naturally occurring yellow-seeded varieties of caraway,” explained Yu. “It would be highly unlikely that mutations would arise simultaneously in all six copies of TT8 that would completely disrupt its function.”

Gene editing hits oil

Thanks to the tools of modern genetics, the Brookhaven team had a way to knock out all six copies of TT8. They used a gene-editing technology known as CRISPR/Cas9 to target specific DNA sequences in the TT8 genes. They used technology to cleave the DNA at these sites and then create mutations that disabled the genes. Yu and team then performed a series of biochemical and genetic analyzes to monitor the effects of their targeted gene editing.

“The yellow seed phenotype we were looking for was a great visual guide for our search,” Yu said. “This helped us find the seeds we were looking for by screening fewer than 100 plants – among which we identified three independently occurring lines in which all six genes were disrupted.”

Results: Seed coat color changed from brown to yellow only in plants in which all six copies of the TT8 gene were disrupted. The yellow seeds had lower levels of “flavonoid” compounds and “mucilage”—both normally produced by biochemical pathways controlled by TT8—than brown seeds from camel strains with unedited genomes.

In addition, many genes involved in oil synthesis and the production of fatty acids, the building blocks of oil, were expressed at elevated levels in the seeds of CRISPR/Cas9-modified plants. This resulted in a dramatic increase in oil build-up. The altered seeds contained another positive surprise in that protein and starch levels were unchanged.

The targeted TT8 mutations were inherited in subsequent generations of camellia plants, suggesting that the improvements would be stable and long-lasting.

“Our results demonstrate the potential for creating new camel lines by gene editing, in this case manipulating TT8 to enhance oil biosynthesis. Understanding more details about how TT8 and other factors control biochemical pathways may provide additional gene targets to increase oil yields, ” he added. Shanklin said.