Unpicking the evolution of land plants
At some point roughly 500 million years ago, plants colonised land. This evolutionary escapade transformed the world as we know it and was followed by a split among plants generating vascular plants such as Arabidopsis, with their elaborate shoot systems and delayed reproduction; and non-vascular bryophytes such as moss. A small signalling molecule known as miR156 evolved in a shared ancestor of both plant groups. In vascular plants, miR156 delays the transition from juvenile development, though non-vascular plants don’t undergo the same transition. “This led us to wonder what the ancestral role of miR156 was during plant evolution, and how important an innovation it was for plants as they emerged from aquatic habitats to colonise the land,” explains Jill Harrison(opens in new window), associate professor in the School of Biological Sciences at the University of Bristol and miR156evo project coordinator. In the EU-funded miR156evo project, undertaken with the support of the Marie Skłodowska-Curie Actions(opens in new window) (MSCA) programme, researchers started investigating the hypothesis that the emergence of the molecule miR156 was a critical part of land plant evolution, enabling the morphological complexity of vascular plants.
Analysing the role of miR156 in plants
To discover the ancestral role of miR156 in land plants, the team began comparing roles for miR156 in moss and flowering plant development. “If it turns out that miR156 has similar effects in both types of plant, for instance regulating the timing of transitions between different stages of plant life cycles, these roles are likely to be ancestral in land plants,” notes Jim Fouracre(opens in new window), Royal Society university research fellow(opens in new window) at the University of Bristol(opens in new window) and researcher on the miR156evo project. To determine what miR156 does in moss, the researchers have both shut down and strengthened miR156 functions. Using genetic transfer techniques, they have changed gene expression levels – essentially whether they are turned on or not. The team also used a relatively new technique known as CRISPR-Cas9, which functions like genetic scissors to cut out pieces of genes. Using this, they can stop genes from functioning altogether, and create ‘reporter lines’ which show where a certain gene is active in the plant. “Early results indicate that miR156 may function similarly in non-vascular and vascular plants in regulating the timing of life cycle progression,” says Fouracre. “Our findings to date suggest that this was likely a conserved function also present in the ancestor of all land plants.”
Expanding our knowledge of ancestral land plants
A particular focus of the project has been the role of miR156 during development of the sporophyte life stage – just before a plant creates spores. “We don’t know what the ancestor of land plants looked like, but the elaboration of the sporophyte life cycle stage in vascular plants enabled their spectacular radiation and rise to ecological dominance,” adds Harrison. “Our investigations into moss sporophyte development will tell us about the ancestral life cycle of land plants.”
Building on fundamental insights into gene regulation
Thanks in part to the award of a MSCA fellowship, Fouracre has now started his own research group as a Royal Society university research fellow, where he will carry forward his investigations into the role of miR156 during plant development. Having developed the necessary experimental tools to start answering research questions, the team is also establishing crop models in the lab to exploit their fundamental insights into how miR156 regulates development. “We are excited about what we will find,” says Harrison.