Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have discovered that the protein responsible for the synthesis of lignin, a crucial plant material, evolved much earlier than previously believed. Lignin is a structural component of plant cell walls with significant impacts on the clean energy industry. This new research explored the origin and evolution of the biochemical machinery that builds lignin and sheds light on the emergence of this key evolutionary event that enabled plant survival in new terrestrial environments. Understanding how plants develop protective mechanisms is essential as they face challenges from climate change.
Modern plants have three types of lignin, with the newest one being S-lignin, which is easier to break down into simple aromatics, making it attractive for industrial applications. The researchers focused on a protein, CB5D, which is crucial for the production of S-lignin but not the older lignin types. In a study published in The Plant Cell, the scientists investigated the evolution of CB5D and its essential role in the synthesis of S-lignin. They found that CB5D has a unique relationship with an enzyme called ferulate 5-hydroxylase (F5H) and that their partnership is responsible for producing S-lignin in flowering plants.
To explore the evolution of CB5D, the scientists ran a genetic analysis to identify other plant species with genes similar to the modern CB5D gene. By synthesizing these genes and expressing them in a modern plant species without the CB5D gene, the researchers found that a gene from a green algae species that evolved over 500 million years ago was capable of restoring S-lignin synthesis. This suggests that the function of CB5D-like proteins was conserved in early land plants, like liverworts and mosses, indicating that CB5D evolved much earlier than expected, partnering with F5H to develop new biochemical machinery for synthesizing advanced lignin structures.
Using confocal microscopy, the scientists confirmed that ancient genes encoding proteins similar to modern CB5D were expressed in the same subcellular structures, highlighting the conservation of this protein’s function over millions of years. The analysis showed that the CB5D-like protein emerged in aquatic algae just before transitioning to a terrestrial environment, suggesting that this protein serves essential functions in plants. Further research is needed to explore the ancient function of CB5D-type proteins and how they changed or expanded over time. This study deepens our understanding of lignin synthesis and highlights the evolutionary adaptations that enabled plants to survive and thrive in new environments.