A gene that regulates the development of roots in vascular plants is also involved in the organ development of liverworts—land plants so old they don’t even have proper roots. The Kobe University discovery, published in New Phytologist, highlights the fundamental evolutionary dynamic of co-opting, evolving a mechanism first and adopting it for a different purpose later.

When scientists discover that a gene is necessary for the development of a trait, they are quick to ask since when this gene has been involved in this and how the evolution of the gene has contributed to the evolution of the trait.

Kobe University plant biologist Fukaki Hidehiro says, “My group previously discovered that a gene called RLF is necessary for lateral root development in the model plant Arabidopsis thaliana, but it was completely new that the group of genes RLF belongs to is involved in plant organ development. So we wanted to know whether the equivalent of this gene in other plants is also involved in similar processes.”

Fukaki turned to the simplest model land plant he could find, the umbrella liverwort Marchantia polymorpha. This plant doesn’t even have roots that can extract water or nutrients from the soil, but it has its own version of the RLF gene.

Using this organism, Fukaki studied the function of its RLF gene and whether its function within the cell is comparable to the Arabidopsis version of the gene.

In the paper, he and his team reveal that liverworts lacking RLF have severe deformations in various organs, demonstrating that RLF is involved in organ development in these basic land plants as well. They could even show that the Arabidopsis gene could perform its function in the liverwort and the liverwort’s gene in Arabidopsis.

“This shows that the two genes are functionally interchangeable as actors in organ development,” explains Fukaki.

The RLF gene produces a protein that belongs to the vast group of heme-binding proteins and that means that it may bind a molecule called “heme,” which is involved in energy transfer within the cell.

Fukaki says, “Given that heme-binding proteins were not known to be involved in organ development in plants, another significant point in our study is that we showed that the RLF protein actually has a heme, both in the liverwort and in Arabidopsis.”

The researcher expects that learning more about how the RLF protein interacts with others will clarify more about the evolution of plant organ development.

Fukaki adds, “The fact that RLF plays an important role in organ development since at least the dawn of land plants is an example of how evolution often co-opts existing mechanisms for new functions, such as for root development, which evolved only after liverworts and mosses branched off the other land plants.”