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How one fern hoards toxic arsenic in its fronds and doesn’t die

Key proteins keep the heavy metal from wreaking havoc on the way to its cellular jail cell

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9:00am, June 4, 2019
Pteris vittata ferns

HEAVY METAL HOARDER  Pteris vittata ferns can sop up and store high levels of arsenic and survive. A set of newly identified genes helps explain how.

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The Chinese brake fern looks unassuming. But Pteris vittata has a superpower: It sucks up arsenic, tucks the toxic metal away in its fronds and lives to tell the tale.

No other plants or animals are known to match its ability to hoard the heavy metal. Now researchers have identified three genes essential to how the fern accumulates arsenic, according to a study in the May 20 Current Biology.

The fern shuttles the heavy metal, often found as arsenate in soil, from the plant’s roots to its shoots. There, the three genes make proteins that help corral arsenate as it moves through the plant’s cells and into a cellular compartment called a vacuole, where the arsenic is sequestered, the team found.

One protein, GAPC1, gloms onto the arsenate, possibly keeping it from doing damage during its journey. Another, OCT4, appears to help arsenate cross membranes, possibly into a structure where a third protein, GSTF1, transforms it into arsenite, the form stored by the plant. Tinkering with the genes caused the plants to die when exposed to arsenic, say Jody Banks, a botanist at Purdue University in West Lafayette, Ind., and her colleagues.

Hot spots

Pteris vittata ferns take up arsenic and store it in their fronds using three proteins, called GSTF1, OCT4 and GAPC1. Scientists forced the trio to reveal their cellular locations by making the proteins glow green, as seen in these microscope images.

Pteris vittata

These ferns are already being used to draw arsenic out of soil in some contaminated areas.  It “takes a long time, but it’s really cheap,” compared with the millions of dollars it can cost to dig out contaminated dirt and clean it, Banks says. In one previous study, the ferns sucked up about half of the arsenic in heavily contaminated soil in five years.

P. vittata is a semi-tropical plant and can’t grow year-round everywhere. But splicing its genes into other plants might make it possible to put more cold-tolerant species to work removing arsenic, Banks says.

Citations

C. Cai et al. Three genes define a bacterial-like arsenic tolerance mechanism in the arsenic hyperaccumulating fern Pteris vittata. Current Biology. Vol. 29, May 20, 2019, p. 1,625. doi: 10.1016/j.cub.2019.04.029.

Further Reading

L. Hamers. Enzymes aid rice plants’ arsenic defenses. Science News. Vol. 191, March 18, 2017, p. 14.

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