University of Copenhagen Discovery of RAK1 Protein Offers New Insight Into How Plants First Evolved to Grow on Land

Moss represents some of the earliest land plants that began to grow on Earth. Photo: Getty Images

(IN BRIEF) Researchers at the University of Copenhagen have discovered a previously unknown protein, named RAK1, that may help explain how plants evolved from simple flat-growing organisms into complex land plants capable of three-dimensional growth. Studied in the model moss Physcomitrium patens, RAK1 appears to link cellular signaling with metabolic regulation, allowing moss cells to divide in multiple directions and form buds and shoots. When the protein was removed, the moss developed defective buds and failed to divide properly, showing that RAK1 may have played an important role in enabling early plants to grow upward and outward. The discovery offers fresh insight into a major evolutionary transition that occurred around 470 million years ago, when plants began adapting to land and eventually gave rise to the forests, flowers, shrubs and ecosystems seen today. The study, published in New Phytologist, involved 18 researchers and was part of an international collaboration with scientists from Austria, England, Germany and Japan.

(PRESS RELEASE) COPENHAGEN, 2-Jun-2026 — /EuropaWire/ — University of Copenhagen scientists have uncovered a biological clue that could help explain one of the most consequential turning points in Earth’s history: the moment early plants gained the capacity to grow beyond flat surfaces and build the upright structures that later shaped terrestrial life. Their research points to a newly identified protein in moss, called RAK1, which appears to help coordinate the cellular processes needed for plants to move from simple surface-level growth into more complex three-dimensional development.

The discovery offers a new perspective on how early plants may have adapted to life on land hundreds of millions of years ago. Before plants developed the ability to grow in multiple directions, their ancestors were limited to simpler, flatter forms. The emergence of three-dimensional growth changed that trajectory, allowing plant cells to organize into buds, shoots and more advanced structures. Over evolutionary time, this capacity helped make possible the diversity of land plants seen today, from mosses and shrubs to forests and flowering species.

The research team studied the moss species Physcomitrium patens, a model organism often used to investigate plant development because of its relatively simple structure and its close connection to early land plant evolution. In moss, growth can occur in two clearly different ways. It can spread across a surface through thread-like filaments, or it can begin forming buds that develop into more complex upright structures. This shift from flat expansion to organized three-dimensional growth is central to understanding how plants became more structurally sophisticated.

RAK1 appears to be important in that process. The protein combines two biological functions that are usually associated with separate protein types: a kinase, which is involved in signaling, and an acetyltransferase, which helps regulate chemical activity inside the cell. This fusion may allow RAK1 to act as a bridge between external growth signals and the internal metabolic control required for cells to divide properly.

To test its role, researchers compared moss plants that carried RAK1 with moss in which the protein had been removed. The moss lacking RAK1 struggled to form normal buds and showed faulty cell division, while moss with the protein was able to produce the structures needed for three-dimensional growth. These results suggest that early plant development depended not only on genetic instructions, but also on the careful regulation of energy use and chemical activity during cell division.

The findings broaden existing explanations of plant evolution. Previous understanding has often centered on gene regulation, especially how certain genes are activated or silenced during development. The University of Copenhagen study adds another layer by showing that metabolism and protein-level regulation may also have been essential to the rise of complex plant forms.

The discovery also illustrates how evolution can generate new capabilities by recombining existing biological parts. RAK1 is thought to have emerged from the fusion of two earlier proteins, creating a new tool that may have helped plants manage the demands of more advanced growth. This kind of evolutionary innovation may have contributed to the transformation of Earth’s surface from largely barren land into plant-covered environments capable of supporting increasingly complex ecosystems.

The study was published in New Phytologist and involved 18 researchers as part of a wider international collaboration with scientists from Austria, England, Germany and Japan. By identifying RAK1 and clarifying its role in moss development, the research provides new insight into the cellular foundations of plant growth and the mechanisms that helped plants establish themselves on land.

Media Contacts:

Cloe De Luxan Hernandez
Assistant Professor
Department of Biology
E-mail: cloe.deluxan@bio.ku.dk
Phone: +45 42 33 80 36

Thomas Juel Ammitsøe
Postdoc
Department of Biology
Email: thomas.j.a@bio.ku.dk
Phone: +45 22 48 21 88

Eleazar Rodriguez
Associate Professor
Department of Biology
Email: eleazar.rodriguez@bio.ku.dk
Phone: +45 93 99 00 63

Amalie Viktoria Gammelgaard
Communications Consultant
UCPH Communication
Email: amalie@adm.ku.dk
Phone: +45 93 51 60 67

SOURCE: University of Copenhagen