At first glance, the ancient water fern Azolla filiculoides is unassuming. It is miniscule by any measure, with gnat-sized leaves that can sit comfortably on the tip of your smallest finger.

But there is more to this miniature plant than meets the eye. Some researchers believe its nitrogen fixation abilities and insect resistant properties could be utilized in agriculture to help feed the world. Others believe that its ability to absorb carbon dioxide at high rates could contribute to the effort to reduce the high concentrations of the notorious greenhouse gas in the atmosphere.

A recent study sequencing the full genome of the tiny fern is the first step to understanding how best to use it to help feed the increasing world population and to fight climate change.

The study represents the first time that a fern genome has been completely sequenced.

The reason is that fern species have notoriously long genomes, making them unattractive options for genome sequencing. Fern genomes are on average 12 gigabases, or 12 billion base pairs of DNA sequences, though some are as long as 148 gigabases. The Azolla’s genome is relatively short, at a modest .75 gigabases.

In the study, recently published in the journal Nature Plants, the researchers sequenced the entirety of the Azolla genome, as well as the genome of a second fern species, Salvinia cucullata.

The project was funded through crowdsourcing, receiving $22,160 — 147 percent of the budgeted goal — from 123 backers on Experiment.com. While the researchers originally planned on sequencing only the Azolla genome, the extra cash allowed them to expand the study and sequence the Salvinia genome as well.

More than 40 scientists from around the world participated in the study, which was led by Fay-Wei Li, a plant evolutionary biologist at the Boyce Thompson Institute (BTI) and an adjunct assistant professor of biology at Cornell University, and Kathleen M. Pryer, a professor in the Department of Biology at Duke University.

Why the Azolla is so important

The Azolla can absorb both carbon dioxide and nitrogen at a high rate, and is genetically encoded with insect resistance.

Because of its unique properties, some scientists believe that the tiny fern could have a major impact across a variety of fields.

“Azolla has a really cool biology and evolutionary history,” said Li. “Azolla engages symbiosis with cyanobacteria for nitrogen fixation, and for this reason it has been used as a green manure and an intercrop for rice paddies in Asia for hundred years.

“In addition, despite its minute stature, Azolla has played a major role in the geological history of earth. Roughly 50 million years ago, a huge Azolla bloom took place in the arctic, drawing down a significant amount of carbon dioxide that likely cooled down the earth for a bit — geologists call this the ‘Azolla event.’ ”

The study

The genome sequence of Azolla revealed the origin of the protein behind the fern’s insect resistance. Unearthing the genetic information behind this property could allow scientists to encode insect resistance into other plant species.

“When you walk into a forest, it’s usually very striking to find that ferns show no sign of insect damage,” said Li. “A few years ago, a highly potent insecticidal protein was isolated from ferns, and when the gene encoding of this protein was introduced to cottons, the transgenic cottons showed a remarkable resistance to insect pests.

“We found this gene to be unique to fern genomes, and likely derived from bacteria via horizontal gene transfer. In other words, ferns’ ability to fend off insect herbivores is likely due to a ‘genetic gift’ from bacteria.”

The study’s genome sequence also revealed key features of the Azolla’s nitrogen fixation capabilities.

The fern has a symbiotic relationship with the cyanobacteria Nostoc azollae, a blue-green phylum of bacteria, that sit in miniscule pockets in the fern leaf and obtain their energy through photosynthesis and produce oxygen. The cyanobacteria fix nitrogen to be used by the Azolla, while the fern provides food for the cyanobacteria in the form of sugar.

Through their analysis of the genome, the researchers demonstrated clear evidence of cospeciation between the Azolla and the cyanobacteria.

It is this property that gives the fern so much potential to be used in agriculture as a natural substitute for nitrogen-based fertilizers. It is also the main reason that it has been used as a green manure and an intercrop for rice paddies for hundreds of years.

But it is the Azolla’s ability to absorb carbon dioxide that has drawn special attention from researchers who believe that the plant could be useful in reducing global carbon dioxide levels.

The thick bloom that covered the arctic millions of years ago pulled in as much as 10 trillion tons of carbon dioxide. Scientists are now studying the plant to see if it could be utilized to a similar effect today.

Sequencing the genome is the first step to understanding how the Azolla may be used in the battle against climate change.

“With this first genomic data from ferns, science can gain vital intelligence for understanding plant genes,” Li said in a statement. “We can now research its properties as a sustainable fertilizer and perhaps gather carbon dioxide from the atmosphere.”

What’s next?

Li believes that the study could have major implications for future research.

As part of the 10K Plant Genomes Project, the researchers are working with the Beijing Genomics Institute in Shenzhen, China to strategically sample the fern tree of life for genome sequencing, said Li.

They already have marked 10 fern species for genome sequencing, making it easy to imagine a near future where the researchers have accomplished this goal.

Doing so would elucidate many mysteries — it may reveal why fern genomes are so large, for example — and generally provide researchers with a far deeper understanding of fern genome structure and evolution.

“Ferns are one of the most speciose branches in the plant tree of life, but no genomic data had been available — in fact, ferns were the only plant lineage lacking a reference genome,” said Li.

“With these two fern genomes, it’s now finally possible to compare gene and genome evolution across the entire tree of life. We anticipate our genomic resources will open up many new research directions and lead to lots of cool discoveries!”