USask team cracks cadmium code in durum wheat

A team of Prairie scientists led by a University of Saskatchewan (USask) researcher has discovered how to significantly reduce the presence of a toxic heavy metal in durum wheat.

The team identified the gene responsible for the accumulation of cadmium in durum, through genome sequencing. The project was part of an international consortium dedicated to sequencing the durum genome, said Dr. Curtis Pozniak (PhD), a USask durum breeder and project leader. Durum is the wheat variety most commonly used as the source of semolina in pasta.

Pozniak credits the depth of expertise within the team for the project’s success. The team included University of Alberta scientists Dr. Gregory Taylor (PhD) and Dr. Neil Harris (PhD), Dr. Ron Knox (PhD) from Agriculture and Agri-Food Canada and Dr. Andrew Sharpe (PhD) from the USask Global Institute for Food Security.

“Andrew and I have complementary expertise in the area of genomics, plant genetics and durum wheat breeding,” said Pozniak. “Our colleagues at the University of Alberta are global experts in heavy metal accumulation in a range of different species. Their contribution to the project was critical to understanding how the gene impacts cadmium movement from the roots to the developing grain.

“It was the perfect marriage of complementary expertise and a proven track record in those particular disciplines.”

The durum wheat genome is quite large and complicated, which meant a collaboration on a global scale was necessary, said Pozniak.

“Our team at USask co-led the project with a number of partners, most notably scientists from Italy’s Council for Agricultural Research and Economics and the University of Bologna,” he said. “Working as part of a team meant we could sequence the durum wheat genome in very short order, given our vast experience in other wheat species.”

So why tackle cadmium? A major reason is because it can have an adverse effect on human health if consumed in sufficient amounts, said Pozniak.

“Cadmium is readily absorbed and retained in the human body, so it can accumulate throughout life,” he said. “It generally accumulates in our kidneys, impacting renal function.”

The Codex Alimentarius—or Food Code—is a collection of standards established by the United Nations and the World Health Organization to protect consumer health. It has set a limit of 200 parts per billion of cadmium in cereal grains. The durum wheat sequence was pivotal to identifying the gene that reduces cadmium levels to 100 or less parts per billion.

“It reduces the levels of cadmium to levels well below international standards, ensuring a safe food supply,” said Pozniak. 

Key to the research was cross-referencing the DNA sequences of cadmium-heavy durum against durum varieties with little cadmium accumulation.

“This comparison was critical to identify precisely the genetic differences between high and low cadmium accumulators. This allowed us to very quickly pinpoint a gene that we thought would be the right gene,” said Pozniak.

The gene identified was a heavy metal transporter that locks cadmium in the roots of durum wheat plants, preventing it from moving to the grain where it can cause harm.

“When we first saw the DNA sequence, it made sense that this might be the actual gene,” said Pozniak. “We conducted very meticulous experiments and were able to confirm that the heavily metal transporter was in fact the gene causing cadmium accumulation.”

The team’s research is already making waves in the crop research community.

“Other crop species can also accumulate cadmium and researchers of these crops have also identified the heavily metal transporter gene that can cause cadmium accumulation in those crops,” said Pozniak.

The sequencing of the durum genome—and genome sequencing in general—has opened up a treasure trove of possibilities where it comes to identifying traits of interest to crop producers, said Pozniak.

“The sequence on its own isn’t all that useful. It’s really a blueprint which allows us to understand which genes are important for those traits that we select for. We are then able to develop DNA tests in a much more effective way to improve varieties for commercial production.”

Pozniak and his partners’ efforts to sequence the durum genome are far from over. There is a focused effort right now to improve resistance to fusarium head blight (FHB) in durum, using much the same process employed in the cadmium project.

“FHB is quite a devastating disease and durum wheat has very little resistance to it,” he said.

That’s not the only sequencing project Pozniak is working on.

“In fact. we have already sequenced 10 additional durum wheat varieties carrying various traits of interest to us in terms of breeding,” he said. “As plant breeders we are trying to simultaneously improve a number of traits, like yield, disease resistance, end-use quality and marketability simultaneously.

“Much like we did with the first sequence, we are deciphering the genetic makeup of those particular individuals, which were carefully selected from our breeding program to represent those traits of interest to western Canadian producers.”

Story from Agknowledge, Fall 2019.