Hornwort genomes provide clues on how plants conquered the land

Over 450 million years ago, plants began the epic transition from water to dry land. Among the first pioneers were the ancestors of humble hornworts, a group of small, unassuming plants that have persisted to this day. New research reveals insights into the genetic blueprints of hornworts, uncovering fascinating details about plant evolution and the early days of life on land.

“We began by decoding the genomes of ten hornwort species, representing all known families within this unique plant group,” said Peter Schafran, a postdoctoral scientist at the Boyce Thompson Institute (BTI) and first author of the study. “What we found was unexpected: hornworts have maintained remarkably stable chromosomes despite evolving separately for over 300 million years.”

Unlike many plants, hornworts have not experienced whole-genome duplication (where an organism’s entire genetic material is duplicated). This absence of duplication has resulted in stable “autosomes”—the chromosomes that hold most of an organism’s genetic material—which have remained relatively unchanged across hornworts despite their deep evolutionary history.

However, not all parts of the hornwort genome are so static. The study revealed the presence of "accessory chromosomes"—extra genetic material that isn't essential for survival but can provide additional benefits. These accessory chromosomes are much more dynamic, evolving rapidly and varying even within individual plants. Additionally, the international team of researchers identified potential sex chromosomes in some species, shedding light on the evolution of plant reproductive strategies.

The study, recently published in Nature Plants, also provided insights into specific plant traits. For example, the researchers uncovered new information about genes involved in flavonoid production (pigments that protect against UV radiation), stomata formation (tiny pores that regulate gas exchange), and hormone signaling. These findings help refine our understanding of how early land plants adapted to their new, challenging environment.

The research project’s extensive genetic investigation of hornworts makes them the most thoroughly sequenced plant group relative to their total number of species.

By creating a comprehensive “pan-phylum” dataset for hornworts, the research team has developed a resource to help scientists comprehend how life on Earth has evolved. It provides insights into how plants might adapt to future environmental challenges and could inform efforts to engineer more resilient crops.

“Our research demonstrates the importance of studying diverse organisms, not just well-known model species,” said Fay-Wei Li, associate professor at BTI and lead author. “By expanding our knowledge of hornworts, we gain a more complete picture of plant evolution and the incredible diversity of life on our planet.”

This research was supported in part by the National Science Foundation.