Unlocking the Genetic Code of Ancient Terrestrial Plants: International Team's Breakthrough

May 2, 2024

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by Dan Moser, University of Nebraska-Lincoln

Around 550 million years ago, plant life first appeared on land. A team of international researchers, including Yanbin Yin from the University of Nebraska–Lincoln, a computational biologist, has unravelled the genomic code of the earliest terrestrial life. These lifeforms paved the way for all other land-based life on Earth, including humans.

The research group, comprised of around 50 scientists from eight different countries, has decoded the first genomic sequence of four Zygnema algae strains, the closest living relatives of terrestrial plants. This research has provided invaluable insights into plant adaptability and is a significant resource for future studies.

The journal Nature Genetics published the study on May 1.

Yin, who co-led the research team with a scientist from Germany, described the research as an evolutionary tale. He stated it answers a critical question - how the first land plants evolved from aquatic freshwater algae.

Within the Department of Food Science and Technology and the Nebraska Food for Health Center, Yin's lab has considerable experience studying plant cell wall carbohydrates, which are essential dietary fiber components for humans and farm animals.

Current terrestrial plant life originated from an evolutionary event known as plant terrestrialization from freshwater algae. The first land plants, also known as embryophyta within the streptophyta clade, emerged around 550 million years ago, drastically altering the planet's atmosphere and surface.

By acting as an evolutionary basis, they enabled the evolution of other terrestrial life, including humans and animals.

The research team worked with four Zygnema strains, two from a US culture collection and two from Germany. A variety of advanced DNA sequencing technologies were employed to decipher the entire genome sequences of these algae.

The strategies used allowed the scientists to generate the organisms' complete genomes at the level of whole chromosomes—a breakthrough for this group of algae. Comparing the genomes with other algae and plants highlighted specific overabundances of cell wall enzymes, signaling genes, and environmental response factors.

Scientists from the University of Innsbruck, the University of Hamburg, and UNL's Center for Biotechnology found a unique feature of these algae using microscopic imaging. It's a dense, very adhesive carbohydrate layer outside the cell walls, known as the mucilage layer.

Lead author Xuehuan Feng, a postdoctoral research associate at Husker, invented a novel and effective DNA removal method to extract this mucilage layer.

Iker Irisarri, a researcher from the Leibniz Institute for the Analysis of Biodiversity Change and also a lead author on the paper, mentioned the fascinating discovery about the genetic blocks that predate land plants by millions of years. These blocks diversified and duplicated in plant and algae ancestors, leading to the evolution of more specialized molecular machinery.

Jan de Vries from the University of Göttingen, another co-leader, emphasized the team's achievement in creating a critical resource for the plant scientific community. Their work unraveled complex connections between environmental responses.

The four multicellular Zygnema algae, which are part of the Zygnematophyceae class, are the closest living relatives of land plants. This class includes over 4,000 individual species of freshwater and semi-terrestrial algae that have adapted to withstand terrestrial stressors.

Decoding genome sequences is key to understanding these adaptations. Previously, only four unicellular Zygnematophyceae genome sequences were available.

Yin stated that the research aligns with one of the National Science Foundation's "Understanding the Rules of Life" principle to face societal issues like clean water and climate resilience. The findings also hold significant potential in applied sciences like bioenergy, carbon sequestration, and water sustainability.

'Our gene network analyses reveal co-expression of genes, especially those for cell wall synthesis and remodifications that were expanded and gained in the last common ancestor of land plants and Zygnematophyceae,' Yin said.

'We shed light on the deep evolutionary roots of the mechanism for balancing environmental responses and multicellular cell growth.'

The international research collaboration includes about 50 researchers from 20 research institutions in eight countries—the United States, Germany, France, Austria, Canada, China, Israel and Singapore. Other Husker researchers on the team are Chi Zhang, professor of biological sciences, and Jeffrey Mower, professor of agronomy and horticulture.

Provided by University of Nebraska-Lincoln