Chen contributes to breakthrough about metal detoxification in plants

With a recent genetic discovery, biologist Sixue Chen and his collaborators may have discovered a way to engineer plants to scrub soils of heavy metal contamination.

In May, the Journal of Biological Chemistry published a paper by Chen and his collaborators. Chen is an associate professor of biology, Genetics Institute faculty member and director of the ICBR Proteomics & Mass Spectrometry core. The paper details results regarding heavy metal detoxification in plants, and how plants synthesize small peptides to protect themselves against heavy metal toxicity.

The paper is titled, “Adaptive Engineering of Phytochelatin-based Heavy Metal Tolerance.” Joseph Jez of Washington University was the lead principal investigator.

Chen and his fellow researchers have been studying the subject for about 15 years, since he was a postdoc in collaborator Philip A. Rea’s lab at the University of Pennsylvania.

Breeding plants that can sequester more toxic metals lends itself to planting species in polluted areas for the purpose of drawing the pollutants out of the soil.

“The natural application you can imagine,” Chen said. “Clean up our water system– clean up our soil.”

When Chen first began participating in Rea and Jez’s research, they were trying to understand how plants withstand heavy metal toxicity. Plants rooted in soils laden with high levels of toxic metals were thriving. The researchers wanted to know why.

“Nature already has this system in place,” Chen said. “We learn this system by studying plants. Our next question is, can we make it more efficient?”

They eventually discovered that plant cells produce a small peptide phytochelatin. This peptide binds to the heavy metals that are absorbed by the plant, then moves them to a receptacle designed to contain the toxin.

Chen likens the process to disposing of a battery in a designated container.

Within the cell, an enzyme phytochelatin synthase uses an antioxidant glutathione to produce phytochelatin. If a plant is in a particularly toxic environment, it begins to use higher quantities of the antioxidant in order to produce the peptide that disposes of the metals. If the plant uses too much of the antioxidant, it experiences oxidative stress. If this is not corrected, the plant’s growth will be compromised– it might even die.

What makes the research in the paper so novel is that Chen and his colleagues have discovered a mutation within the gene that encodes the enzyme. This mutation enables the cell to produce higher amounts of phytochelatin, while not disturbing the cell’s antioxidant homeostasis.

Chen and his colleagues want to find ways to make organisms more efficient.

“This one is really exciting,” Chen said. “Because natural evolution is slow, and now we have the modern biological approaches and technologies that allow us to accelerate the natural evolution processes.”