These organisms have been adapting for 500 million years

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With the new knowledge of the brown alga genome, researchers can study how kelp and seaweed have adapted to changing environments over hundreds of millions of years. Photo: Galice Hoarau

These organisms have been adapting for 500 million years
They play a key role in coastal ecosystems and are threatened by climate change. Now, researchers have characterized the genomes of 60 brown algae species from around the world.

Like a dark shadow beneath the surface, kelp forests spread across the seabed. Newly hatched fish dart around among the swaying fronds. On the sturdy kelp stalks grow bryozoans, cnidarians, and other peculiar creatures.

Brown algae play a unique role in Earth's ecosystems. They perform photosynthesis, capturing megatons of carbon annually – like the great forests on land.

They are also foundational to coastal ecosystems. In some kelp forests, animal life reaches over 100,000 individuals per square meter.

Professor Galice Hoarau is reluctant to call brown algae plants—they are too unrelated. However, as vegetation, brown algae can be found globally. Among marine algae, brown algae dominate.

"When we talk about marine forests, it’s about brown algae. Most of the seaweed you see on rocks along the shore is brown algae. They provide habitats for other species, extract nutrients from the water, and offer physical protection by dampening currents and waves. They play a very important role," says Professor Hoarau.

Galice Guillaume Hoarau is professor at the Faculty of Biosciences and Aquaculture at Nord University.

Now, researchers from 35 institutions and universities worldwide, including Nord University, have collaborated to characterize the genes of brown algae. The genomes of more than 40 species from 16 families have been sequenced and annotated, offering a unique opportunity to study the genetic make-up of these algae.

For PhD student Ananya Khatei, this has opened new doors for research.

“Finally, the genes of the algae have entered the public domain. We can now begin to explore how the genome is organized and how the genes are regulated. These algae have experienced several periods of climate change, and we can now study how they developed the ability to adapt”, Khatei says.

Khatei is doing research on epigenetics, the molecular mechanisms that turn genes on and off. One common mechanism is methylation, where the chemical compound methyl attaches to the DNA molecule.

Khatei has discovered that DNA, the very code within the genes, is strongly influenced by the type and degree of such methylation.

"This indeed plays a huge role in the evolution of organisms. So the DNA we see today not only tells us the past story of how it was shaped but predicts how epigenetics is going to shape it up in future along with the change in environmental conditions."

Researchers can now trace changes in genes when a new branch of species emerges and link these changes to shared physical traits within that branch.

"For example, the development of alginate production is a shared trait among several species. Similarly, the development of what we call plasmodesmata — a channel system in the cell wall that allows cell communication — is another," Hoarau explains.

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Ananya Khatei has been a Ph.D. student at Nord University. She is now a researcher at ICAR - Directorate of Coldwater Fisheries in Bhimtal, India. Private photo

The development of plasmodesmata was crucial in the evolution of multicellular organisms. It allowed brown algae to grow large, with different parts of the algae body taking on specialized functions.

"Remember, they live in tidal zones with strong currents and waves. Some kelp species can grow 15–20 meters tall," says Hoarau.

Brown algae have also developed specialized cells to anchor them to the substrate—an evolutionary milestone researchers date to 250 million years ago, coinciding with one of Earth’s largest mass extinctions, when 83% of species went extinct.

About 50 million years later, as the supercontinent Pangaea broke apart and today’s oceans formed, brown algae developed a life cycle system alternating between different body forms from one stage to the next.

Researchers believe this period also saw the emergence of the great kelp forests. The ability of Norwegian brown algae to withstand drying out during low tide developed about 100 million years ago.

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Genetic diversity is crucial for species to adapt to a changing environment. Photo: Griffin Hill

Now, centuries of evolution and adaptation may be wiped out by climate change. Brown algae are cold-water species and struggle when exposed to high temperatures for extended periods. Marine heatwaves can be devastating for them.

But it is also possible that they will once again manage to adapt. Alexander Jüterbock studies how algae adapt to warmer environments.

“We see that brown algae have an ability to "remember" the stress they have been exposed to, allowing them to better withstand it when they encounter it again. It can be compared to a form of vaccination, where this "memory" can be transferred from one generation to the next”, he says.

Mann med redningsvest i båt
“We see that brown algae have an ability to "remember" the stress they have been exposed to, allowing them to better withstand it when they encounter it again” says researcher Alexander Jüterbock. Photo: Griffin Hill

The answer to which molecular mechanisms are behind this lies in the epigenome, the researcher believes.

“Brown algae differ significantly from plants and animals. Evolution has taken a completely different path. Brown algae have different enzymes that regulate genes, determining which genes to be turned on or off,” says Jüterbock.

Hoarau emphasizes that the study's results have provided researchers with new tools to study and to protect these algae.

"Genetic diversity is crucial for species to adapt to a changing environment. That’s why it’s important to know if we have genetically unique populations or those with low diversity. Losing a population with high diversity also means losing the potential for adaptation," Hoarau says.

Understanding their genetics is also critical for the growing algae industry. Brown algae are harvested for medical uses and food production, and more voices are calling for industrial cultivation of brown algae.

"Having a complete overview of the genome is a significant advantage," says Hoarau.

Source: Evolutionary genomics of the emergence of brown algae as key components of coastal ecosystems - ScienceDirect

Facts: Epigenetics

Epigenetics refers to molecular mechanisms that have the potential to determine if genes are switched on and off in cells. These mechanisms can be inherited across generations.

The prefix "epi" means "in addition to," so epigenetics refers to information that comes in addition to the genetic material itself, meaning in addition to variation in the DNA sequence of a gene

There are three types of epigenetic mechanisms:

  • DNA methylation (a chemical methyl-group attaches to a specific region on the DNA strand),
  • Histone modification (methyl or acetyl groups attach to the proteins around which the DNA strand is wound),
  • Small non-coding RNAs small non-coding RNA strands inhibit the generation of proteins coded by the genes.

While the term "genome" describes the entire collection of genetic material in an organism, the term "epigenome" encompasses all the epigenetic modifications within the organism.

Epigenomics is a field where researchers aim to map and understand the function of all the epigenetic mechanisms that regulate the expression of our genetic material.

Sources: Store medisinske leksikon and The Norwegian Biotechnology Board

Facts: The History of Brown Algae

The first brown algae are believed to have emerged 450 million years ago during a period known as the Great Ordovician Biodiversification Event (GOBE).

During this time, there was a significant increase in atmospheric oxygen levels. In the oceans, new herbivorous species appeared, which may have driven the evolution of more multicellular and complex algal species.

The newcomer distinguished itself from its ancestors (unicellular or simple filamentous red algae) through several unique traits that laid the foundation for its success:

  • Cell Wall Development: They developed a cell wall made of specific complex sugars, providing extra protection and enabling survival in tidal zones where they are periodically exposed to air.
  • Halogen Utilization: They began to use a specific group of compounds—halogens—in their metabolism, which protect them against bacteria, UV radiation, and stress.
  • Adaptable Life Cycles: They evolved a range of life cycles suited to different marine environments.