The Evolution of Multicellular Seaweed

A recent study published in the journal Molecular Plant sheds light on the genetic underpinnings that allowed macroalgae, commonly known as seaweed, to evolve multicellularity. Researchers discovered that three lineages of macroalgae independently developed multicellularity by acquiring genes that facilitate cell adhesion, extracellular matrix formation, and cell differentiation. Surprisingly, many of these genes had viral origins.

The study, led by algal biologist Alexandra Mystikou and bioinformatician David Nelson from New York University Abu Dhabi and the Technology Innovation Institute, United Arab Emirates, significantly increased the number of sequenced macroalgal genomes from 14 to 124. This comprehensive genomic analysis is the first of its kind to explore the evolution of macroalgae through a genomic lens.

Macroalgae, which exist in both fresh and seawater, are complex multicellular organisms with distinct organs and tissues. They belong to three main groups—red (Rhodophyta), green (Chlorophyta), and brown (Ochrophyta)—which evolved multicellularity at different points in time. Rhodophytes and Chlorophytes developed multicellularity over a billion years ago, while Ochrophytes only achieved this milestone in the past 200,000 years.

By sequencing 110 new macroalgal genomes from various species across diverse habitats and climates, the researchers identified metabolic pathways that differentiate macroalgae from microalgae. These pathways may contribute to the success of invasive macroalgae species, with many of the identified metabolic genes originating from algae-infecting viruses. Moreover, genes with a viral origin were particularly abundant in the more recently evolved brown algae.

The researchers found that as macroalgae transitioned to multicellularity, they acquired new genes not found in microalgae. These genes were involved in cell adhesion, cell differentiation, cell communication, and inter-cellular transport—essential processes for the development of specialized cellular functions.

The study also highlighted distinct features among the different macroalgal lineages. Rhodophytes exhibited greater diversity between species due to their longer evolutionary history of multicellularity, while Chlorophytes shared genomic similarities with land plants, suggesting the presence of these genes in a common ancestor.

The research team is eager to delve further into the dataset to explore environmental adaptations and habitat preferences among macroalgae. Future research aims to sequence and analyze even more macroalgal genomes to uncover additional insights into their evolution.

The study was supported by the NYUAD Faculty Research Funds and Tamkeen. For more information, refer to the publication in Molecular Plant titled “Macroalgal deep genomics illuminate multiple paths to aquatic, photosynthetic multicellularity.”