400 Million Years of Food Transport in Plants: unearthing the origin, diversity and genetic toolkit of vasculature

Distribution of water, mineral nutrients and food throughout the plant is carried out using an internal plumbing system made up of two highly specialised tissues - xylem and phloem. The acquisition of these specialised tissues during plant evolution was one of the key innovations that allowed plants to evolve from tiny moss-like species into the towering trees and the diversity of crop species that dominate the landscape today. The xylem and phloem are intimately linked, but functionally different, with the xylem transporting water and the phloem transporting food throughout the plant. All economically important plants, whether crop or forest species, rely on the transport of food, in the form of sugars, through the phloem. However, despite the key role that the phloem plays in all parts of plant life, we do not know how the structure and function of the phloem will change, or can be engineered to respond, to future climate change. A vital line of evidence for predicting how the phloem will likely change in the future is preserved in the previously unexplored fossil record of plants that lived through prehistoric episodes of global climate change, and extremes of atmospheric CO2.

The aim of the proposed research is to investigate key unanswered questions about the evolution of the phloem, one of the most important but least well understood plant tissues. I will transform our knowledge of phloem evolution by tackling three overarching questions: (i) when did the phloem originate, (ii) how has its structure, function and genetic toolkit evolved over the past 400 million years, (iii) how has phloem evolution been driven by climate change? To answer these questions I will combine cutting-edge 3D imaging of fossils, computational modelling of phloem function never before undertaken with fossils, and comparative genomic analyses of living plants. To answer these key questions I have identified three objectives for the Fellowship:

1. Define the origin of the phloem in land plants
2. Reveal major evolutionary innovations in phloem structure and function in relation to climatic change through geological time.
3. Characterise the genetic innovations that underpinned the diversification of the phloem

Combining studies of living species, fossils and genes, I will draw evolutionary conclusions about the phloem that none of these lines of evidence alone could achieve, marking a step change in our understanding of phloem evolution. The impact of this study will be to shed light on the evolution of this crucial plant tissue and to help understand how the structure and function of the phloem is tied to the level of atmospheric CO2. The findings of the Fellowship will therefore be essential for predicting how the phloem structure of living plants, including economically important crop and tree species, will likely respond in the next 50 to 100 years to rising atmospheric CO2 caused by anthropogenic climate change.

I will be uniquely placed at the University of Edinburgh to carry out this programme of research. The School of Biological Sciences (SBS) is a world leader in studying the structural, functional and genetic changes that underpin complex plant traits in diverse lineages. In addition, my Fellowship will benefit greatly from collaboration with the palaeobiology group in the outstanding School of Geoscience and the collections of the two project partner organisations; the fossil plants in the National Museum Scotland (NMS) and living collections in the Royal Botanic Garden Edinburgh (RBGE). In particular, the NMS contains a unique and unexploited collection that will be essential for my proposed research. Taken together, the excellent research environment in SBS, strength in palaeobiology in the School of Geoscience and access to the collections of the project partners makes this a Fellowship that could not be successfully accomplished anywhere else in the world.

The aim of this project is to take an interdisciplinary approach to describe the evolution of the phloem over its 400 million year history. The results of the study will have a broad impact across a range of sectors. Here, I have identified the five major sectors that will benefit from the proposal and in each case I have outlined who the benefices are and how they will benefit:
1. Academic
The academic beneficiaries are described in detail in the 'Academic Beneficiaries' section. They cover a wide range of scientists studying interdisciplinary questions in both the Biological and Geological Sciences. They will benefit from the proposed research as it answers fundamental questions in plant evolution about the origin and evolution of the phloem and predicts how the phloem will likely change in the future in response to climate change.
2. Commercial
Although the work in the proposal is fundamental in nature and aims to tackle outstanding questions in plant evolution there is significant potential for commercial impact. The agricultural sector will be the most likely to benefit from the findings, especially those tasked with breeding crop varieties more resistant to growth in a changing environment and climate. This group will benefit from knowing how the phloem responded in the past to climatic and environmental fluctuations and will therefore likely respond in the future to comparable change. In the Fellowship I aim to identify orthologs of known phloem developmental regulators in crop species and to test if their gene expression profiles are conserved with those of the model species Arabidopsis thaliana. Additionally I will identify putative candidate genes controlling phloem development. Understanding the evolution and the genetic control of the phloem is an essential starting place for engineering the phloem in crop species in the future.
3. Policy
Policy beneficiaries include those developing UK and international policy with respect to global food security. A line of evidence to help predict how plants will respond to environmental and climate change in the future is to understand how they responded to similar crises in the past. The output of the project will be an example of the way in which fossil plants can be used to help predict changes in plants in the future. This is a line of enquiry that I hope to feed back to policy makers through publications, interactions with the media and direct correspondence with policy makers - in particular at the catalyst meeting I intend to organise.
4. Public sector
The public sector beneficiaries are the two project partners of the study, Royal Botanic Gardens Edinburgh (RBGE) and National Museums Scotland (NMS). The major impact for both the partners will be my promotion of their collections. Promoting their collections in all forms of publications, conference talks and public engagement event will raise awareness of the collections with the aim of encouraging others to make use of these excellent collections in the future.
5. General Public
The general public will be exposed to the research through public engagement events such as Fascination of Plants Day and the Edinburgh Science Festival, and through the dissemination of the research though media channels. Of particular importance for the current project is to promote and publicise the Rhynie chert as a fossil site of National Scottish importance. Despite being one of the most important fossil sites in the world it is currently under represented and publicised: an aim of the project is to raise the profile of this site among the general public with the help of NMS. Finally, though my public engagement events I will raise awareness about the impact of climate change on food security with the aim of inspiring the next generation of scientists to tackle these key questions.