An overview of our research
During the past 500 million years land plants have evolved a staggering variety of diverse forms and intricate functions that have enabled them to diversify and transform the Earth. Here in the Molecular Palaeobotany and Evolution Group we investigate the evolution of characteristics that were key for the success of land by plants.
Taking interdisciplinary approaches at the interface between the Life and Earth Sciences we shed light on the evolution of key innovations such as the phloem and roots.
Below are brief descriptions of current and previous work from the group but we are also keen to expand our research to cover other major innovations so please get in contact if you would like to discuss research outside of the projects listed below.
Plants require an internal conducting network to transport food and water around their bodies. This conducting network is termed vasculature and consists of two tissues, water conducting xylem and food conducting phloem.
The acquisition of these tissues during plant evolution was key for the origin of trees and crops from tiny moss-like ancestors.
Despite the importance of the phloem for transporting sugars throughout plants we know almost nothing about its evolution or how it may respond to climate change. The current aim for the group is to investigate the evolution of the phloem.
Lateral plant organs, including leaves and reproductive structures, are arranged on stems in distinct patterns termed phyllotaxis. Of the many types of phyllotaxis that exist spirals are the most common. Spirally arranged organs are incredibly widespread in plants and you may be used to seeing them in leaves, flowers and pine cones. What’s amazing about these spirals is that when quantified we find that they are almost always described by integers of the famous mathematical series – the Fibonacci series. In fact, in living species today >90% of botanical spirals are Fibonacci spirals. Why Fibonacci spirals are so common in plants today has perplexed scientists for centuries, and remains a major unanswered question. Investigating this question is major aim for the lab.
In recent work we demonstrated that non-Fibonacci spirals, that are rare in species today, were present in the earliest group of leafy plants, (Turner et al., 2023 Science, https://doi.org/10.1126/science.adg4014). This finding suggests that the prevalence of Fibonacci spirals may have changed through time and there may have been times in the geological past when Fibonacci spirals were less common than they are today. A question we are currently investigating.
The Rhynie chert is one of the most important fossil sites in the world and is located roughly three hours drive north of Edinburgh by the small village of Rhynie in Aberdeenshire. The fossils at Rhynie preserve a 407 million year old ecosystem frozen in time with exceptional preservation. They provide a unique glimpse into early life on land and of the diversity of plants, animals, fungi and microorganisms on the early terrestrial surface. We have been using new techniques to digitally reconstruct the plant life in the Rhynie chert and characterise the diversity of organisms present at this key site.
Scotland is home to a number of amazing palaeobotanical localities, including the world famous Devonian Rhynie chert, important early Carboniferous sites including Oxroad Bay and the Pettycur limestone and more recent fossils from the Jurassic. In the lab we have a number of projects focused on studying these exceptional plant fossils. For this work we collaborate closely with the Geobiology and Geochemistry group in the School of Geosciences at Edinburgh University and with National Museums Scotland.
Before moving to Edinburgh my research was focussed on the evolution of rooting systems carried out in collaboration with Prof Liam Dolan. Some research highlights from our work include:
- Many genes involved in rooting system development evolved before plants came to land. Reference: Catarino & Hetherington et al., (2016) Molecular Biology and Evolution
Early vascular plants lacked roots and instead developed rhizoid based rooting systems. Reference: Hetherington & Dolan (2018) Philosophical Transactions of the Royal Society B
Roots evolved separately at least twice in land plants and lycophyte roots evolved in a stepwise manner. Reference: Hetherington & Dolan (2018) Nature
There were multiple origins of dichotomous and lateral root branching. Reference: Hetherington, Berry and Dolan (2020) Nature Plants
Roots of giant extinct lycophyte trees were similar to the roots of living lycophytes today. References: Hetherington, Berry and Dolan (2016) Proceedings of the National Academy of Sciences, Hetherington & Dolan (2017) New Phytologist, Hetherington et al., (2019) bioRxiv
Some root meristem types are now extinct today. Reference: Hetherington et al., (2016) Current Biology
Although the main focus of the group is now on phloem evolution, the origin of roots and phloem were tightly linked and we are keen to establish how the co-evolution of these two innovations altered plant evolution.
Progress to study the evolution of gene function in vascular plants is currently limited by a lack of a lycophyte model species that is amenable to genetic manipulation and classical genetic approaches. The species Selaginella apoda was proposed as an ideal candidate for a model lycophyte over a decade ago due to its small genome and fast generation time.
We are currently growing S. apoda in the lab and developing protocols to aid in growth and propagation of the species. These approaches will lay the groundwork for the hopeful genetic transformation of the species in the future.