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

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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 plants2. 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 phloemCombining 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.