macro photo of broccoli

Rapeseed genes could take the bite out of broccoli

Scientists have unraveled the genetic code of the rapeseed plant—which could lead to better canola oil—and possibly to less bitter broccoli.

Published in the journal Science, the findings will help scientists understand how plant genomes evolve in the context of domestication. Brassica plants have been bred all over the world for centuries and resulted in produce and products diverse enough to show up in several different supermarket aisles.

Broccoli, cauliflower, Brussels sprouts, Chinese cabbage, turnip, collared greens, mustard, canola oil—all these are different incarnations of the same plant genus, Brassica.

“Whole-genome sequencing efforts like this one allow us to address two fundamental questions,” says Eric Lyons, assistant professor in the School of Plant Sciences at University of Arizona.

“How does the genetic information stored in the genome help us understand the functions of the organism, and what does the structure of the genome tell us about the evolution of genomes in general?”

The study shows that the rapeseed (or Brassica napus) genome contains a large number of genes—more than 100,000—due to the fact that it arose from a merger between two parent species, Brassica rapa (Chinese cabbage) and Brassica oleracea, a cultivar that includes broccoli, cauliflower, Brussels sprouts, collard greens, and others.

rapeseed flowers
Scientists report that the rapeseed genome contains a larger number of genes because it arose from a “merger” between two other species. (Credit: Tom Ellefsen/Flickr)

What kids hate to eat

“The rapeseed genome has a very interesting history,” says Haibao Tang, a senior scientist of bioinformatics. “As a result of the merger event, it ended up with four copies of each gene. In this study, we looked at what happened after this merging event. For example, what genes were gained and what genes were lost.”

The Brassica group is extremely versatile with regard to human use,” he says. “In all of the cultivars, we find something to eat. The genome defines what Brassicas are.”

“It also defines what kids hate to eat,” Lyons says. “The bitterness in some cultivars such as broccoli or Brussels sprouts comes from a class of compounds called glucosinolates, and we find that precisely those genes that code for those compounds were lost from the rapeseed genome.”

Change the biochemistry

The sequencing effort provides scientists and breeders with a map they can use to home in on certain genes and, by extension, the plant’s metabolic pathways. For example, they could strive to create a cultivar of broccoli that’s not bitter, or tweak the lipid biosynthesis pathway to favorably modify the oil content in rapeseed.

Being able to modify the content of bitter-tasting compounds has implications beyond what meets the tongue, because in most plants, those chemicals also confer defense against pests.

“Depending on the cultivar in question, breeders may want to change the biochemistry,” Lyons says. “You could knock down chemicals you don’t want and ramp up others you do want. Or you may want to change the shape of the plant or parts of it.

“With Chinese cabbage, for example, we don’t care too much about its oil content, but the size and shape of the leaves and how they taste. With rapeseed, it’s the other way around.”

The National Science Foundation funds the iPlant Collaborative of University of Arizona’s BIO5 Institute, which provided computational power and cyber-infrastructure for running the analyses.

Source: University of Arizona