28 June 2018

DNA of fast-growing Azolla sequenced

First fern genome comes from Utrecht ditch

Cover van Nature Plants met de eerste twee varens waarvan het genoom is bepaald
The cover of Nature Plants: The two ferns for which the genome has been sequenced: Azolla filiculoides (back), and Salvinia cuculata (front)

Scientists have recently sequenced the first full fern genomes. The project involved two species of fern, of which one, Azolla filiculoides was found in a drainage ditch near the Galgenwaard football stadium in Utrecht. The fern’s genome was sequenced by researchers at Utrecht University, who have been studying this extremely fast-growing fern because of its potential as a sustainable alternative to other crops, such as soy. The results of their research were published in the scientific journal Nature Plants on 2 July.

Fern genomes are much larger than that of humans, and they are currently considered to possess little economic value. These challenges have prevented the sequencing of complete fern genomes until this international partnership was set up with the help of crowdfunding, explains Henriette Schluepmann from Utrecht University.

Alternative for livestock feed

Sloot met Azolla, Montfoort
Ditch with Azolla in Montfoort

Schluepmann and her colleagues in Utrecht, including second author Paul Brouwer, have been studying Azolla filiculoides, commonly known as mosquito fern, for some time. The floating freshwater fern may have economic potential, starting with using it as an alternative to livestock feed. “We import more soy to the port of Rotterdam to feed our livestock than we could ever grow in the Netherlands. Growing Azolla might be a sustainable local alternative”, explains PhD Candidate Laura Dijkhuizen. 

Twice as large in one week

Azolla grows all over the world, and during the Dutch summer, the plant can grow twice as large in just one week’s time. The plant itself is difficult to digest, but its many proteins means that it might be useful as a raw material for livestock feed.

Double photosynthesis

Azolla’s rapid rate of growth is made possible by a unique symbiosis with a bacterium that lives in the fern’s leaves. This cyanobacterium absorbs nitrogen in the air through its own photosynthesis process, and shares it with the plant. Most plants can only absorb nitrogen from the soil, where it is often a limiting factor for growth. But thanks to its symbiosis with the bacteria, Azolla has a ‘double photosynthesis’, which facilitates rapid growth and protein production.

Het drijvende varentje Azolla
The leaf of the Azolla fern has two parts. The bottom half is transparent, and acts as a flotation device. The upper half is thick and dark green, and is home to the bacteria that fix nitrogen, which help the plant to grow extremely fast.

Completely different mechanism

Another group of plants also contain cyanobacteria that remove oxygen from the air and share it with the plant, so scientists assumed that the plants would share at least the same genes and molecules with Azolla. But now that the Azolla genome has been sequenced, it seems that the mechanism behind it is very different. “With this genome research, we have learned quite a bit more about the metabolism of these ferns”, Schluepmann says.

Evolving together

The study also conformed the suspicion that Azolla and the cyanobacteria evolved together. This was possible because the spores that the fern spreads contain a special compartment for the bacteria. This process of co-evolution had not yet been proven, because the Azolla genome had not been fully sequenced.

Without fertiliser

Schluepmann: “This research fills a big gap in our knowledge about plant evolution. It also deals with a floating species that achieves an extremely high rate of growth and protein production, all while floating in water without fertiliser containing nitrogen. We may be able to use this first fern genome to select for fern species that are suitable for aquaculture.”

On the cover

The first fern genomes were received enthusiastically in the scientific community - so enthusiastically, in fact, that both ferns were featured on the cover of Nature Plants.

Publication

‘Fern genomes elucidate land plant evolution and cyanobacterial symbioses’
Fay-Wei-Li, Paul Brouwer*, […], Henriette Schluepmann*, Gane K.-S. Wong, Kathleen M.Pryer;
affiliated with Utrecht University
Nature Plants, 2 juli 2018, https://doi.org/10.1038/s41477-018-0188-8

This research was part of Future Food Utrecht, one of the four hubs within Utrecht University’s trans-disciplinary research programme  Pathways to Sustainability.

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