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Arsenic resistant plant could lead to new crop of natural soil cleaners

Thursday, 06 June 2019

Researchers have discovered how a common houseplant can absorb and withstand arsenic, a find which could lead to the development of new plant varieties that will clean contaminated soil.

A new study led by researchers from Purdue University in Indiana and in collaboration with the University of Nottingham has revealed how a fern – Pteris vittata, also known as the Chinese brake fern could hold the key for cleaning contaminated soil due to its unique ability to hyper-accumulate and tolerate very high levels of arsenic that it takes up from the soil by isolating the toxic element in its leaves.

Arsenic is one of the most common contaminants of land in the UK and can pose a threat to human health. Decontaminating land found to have arsenic in is a costly and time-consuming process often using heavy engineering techniques including excavation, disposal and capping.

The research published in Current Biologydescribes the genetic and cellular mechanisms of the fern and could lead to the modification of other plants that would remediate arsenic from contaminated soils more quickly and efficiently.

Guarding against effects of arsenic

Once inside cells - both human and plant – arsenic leads to cell death either through oxidative stress or by interfering with the cell’s ability to produce ATP - a molecule that provides energy for cells. But the fern has mechanisms that guard against these effects.

Three genes were identified that are highly active when the fern comes into contact with arsenic.  Silencing each of these genes leads to death of the plant in the presence of arsenic, demonstrating their importance in arsenic tolerance. By testing the functions of the proteins encoded by these genes, they showed that these proteins may work together to essentially neutralize arsenic once inside the cell.  

Jody Banks, Professor of botany and plant pathology at Purdue said: “Other researchers have shown that this fern, when grown on arsenic-contaminated soils, can remove almost 50 percent of the arsenic in five years, it takes time, but it’s cheap. Our research goes a step further showing how the plants genes work together to mop up arsenic inside a cell until it can be stuffed safely away in the cell’s vacuole where it can’t do any harm.”

The genes program three proteins – OCT4, GST and GAPC1. The team showed that OCT4 is a membrane protein, controlling the transfer of compounds through the cell membrane. GST is an arsenate reductase, which serves as a catalyst to turn arsenate from the soil into arsenite, the form of arsenic that can be sequestered.

Evolving tolerance

The GAPC1 protein in other plants uses phosphate to help break down glucose for energy, and arsenate interferes with its normal function. In Pteris vittata fern, however, GAPC1 has a higher affinity for arsenate than phosphate, allowing the plant to grab arsenate and convert it into a compound that OCT4 can then pump into the vacuole for storage, where GST then chemically converts the trapped arsenate into arsenite. This allows the fern to tolerate the otherwise toxic substance.

Other researchers have discovered a bacterium, Pseudomonas aeruginosa, that has a similar way to tolerate arsenic. The genetic mechanisms in the bacterium and the fern are nearly identical, suggesting that the fern and the bacterium independently evolved similar arsenic tolerance mechanisms

David Salt, Professor of Genome-enabled Biology at the University of Nottingham has worked with Dr Banks for over 15 –years on arsenic tolerance in P. vittata, he said “We have been working on the mechanisms of arsenic tolerance in this fern for many years and it is really gratifying to make such an exciting new discovery. What we have found is new biology in plants, which offers new avenues for applications in environmental restoration, food safety and public health.”

Understanding the genetic and cellular mechanisms that allow the fern to accumulate and tolerate arsenic is an important step in developing other plants that could remediate arsenic-contaminated soils and waters more quickly.

The US National Science Foundation funded this research. 

Story credits

More information on the is available from Professor David Salt at the University of Nottingham on David.salt@nottingham.ac.uk

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