This tiny fern could help fight climate change

Genome map shows this little plant could be a big game changer.

A tiny Azolla filiculoides placed on a person's fingernail.

The Azolla filiculoides fern is tiny but mighty. (Photo: Fay-Wei Li)

A fern with leaves no larger than a gnat could be one of the most important plants on Earth.

Researchers have sequenced the genome of Azolla filiculoides, a bright green fern with a long history, and they've discovered the genes that give the fern some incredible abilities: It's able to "fix" nitrogen on its own, to ward off insects and to be a carbon sink.

This fern is a triple threat

A. filiculoides is a water fern, and it can grow quickly, sometimes taking over a lake in a matter of months. For water-based crops like rice, this is a real boon. A. filiculoides has been used as "green manure" in rice paddies in Asia for well over 1,000 years because of its symbiotic relationship with the cyanobacteria Nostoc azollae. The fern and the bacteria work together to capture nitrogen from the air and convert it into something the fern and other surrounded plants can use. This eliminates the need for nitrogen-added fertilizers.

Most plants can't capture nitrogen like this, even though nitrogen is one of the key nutrients plants need. As a result, many fertilizers add nitrogen, often in the form of ammonium nitrate. But too much nitrogen is a problem for plants — they can grow too fast, and at the expense of flowering and fruiting — and it's also a problem for the environment. Nitrogen runoff stimulates the development of algae blooms and other pesky plant life in water.

"Now that we have genomes available for both the fern and cyanobacterium, there is great promise for tapping into the secrets of this natural biofertilizer that may help lead to future sustainable agricultural practices," Kathleen Pryer, a biologist at Duke University involved in the study, said in a statement released by the Boyce Thompson Institute.

Azolla filiculoides in the Botanical Building at Balboa Park in San Diego Azolla filiculoides grows quickly, and that's a good quality in a carbon sink. (Photo: Stickpen/Wikimedia Commons)

The sequenced genome also revealed the gene A. filiculoides uses to keep insects at bay, and that gene is like a "genetic gift" from the bacteria, according to Fay-Wei Li, a professor at Cornell's Boyce Thompson Institute and the lead researcher on the study. The "gift" is specific to ferns — most other plants lack the ability to naturally ward off insects — and it likely first appeared in a gene transfer between ferns and a bacteria.

While A. filiculoides is found mostly in temperate and tropical regions these days, 50 million years ago, the planet was a lot warmer, and you could find A. filiculoides in the Arctic Circle. Even then, the plant rapidly grew, and it pulled some 10 trillion tons of carbon dioxide from the atmosphere, contributing to the rapid cooling of our planet. Growing a huge amount of this tiny fern might help us to soak up carbon dioxide that is contributing to climate change today.

Public gives science a hand

Sequencing A. filiculoides was an uphill battle. Ferns have notoriously large genomes, some of which are as large as 148 gigabases, the equivalent of 148 billion base pairs of DNA sequences. (For comparison, the human genome is about 3 billion base pairs.) Most fern genomes are around 12 gigabases.

The genome for A. filiculoides is a mere .75 gigabases, and it's the first fern to have its genome sequenced.

Pryer had been attempting to secure funding for a fern sequencing project for almost 20 years. "I was met with responses like 'too unconventional' and 'not important enough'," she said.

So she and Li turned to crowdsourcing the raise the money to sequence A. filiculoides. Putting their call up on Experiment.com in 2014, the two researchers secured enough funding sequence the fern. Their efforts caught the attention of the Beijing Genomics Institute (BGI), and that organization offered to sequence the genome free of charge. More researchers came on board, and between the supplied funds through Experiment.com and the Beijing Genomics Institute's support, researchers managed to sequence not only A. filiculoides, but also for Salvinia cucullata, another floating fern.

The researchers published their results in the journal Nature Plants.

This isn't the end of the fern sequencing, however.

"We are going fernatic to sequence more ferntastic genomes!" said Li. "As part of the 10K Plant Genomes Project collaboration, we are working with BGI to strategically sample the fern tree of life for genome sequencing. Currently we have about 10 fern species in the sequencing pipeline."

That's 10 more ferns with who-knows-how-many secrets that could help our planet.

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