Origin and co-evolution of land plant-fungal symbioses through the "greening of the Earth"

Colonization of the land by terrestrial plants ca. 475 Ma was one of the most far-reaching chapters in Earth's history. Liverworts occupy the pivotal position in the land plant evolutionary tree with a wide variety of evidence supporting these non-vascular plants as the most basal terrestrial photosynthetic organisms and amongst the earliest colonizers of the land ca.475 Ma. Recent molecular genetic evidence supports the view that mycorrhiza-like associations in liverworts are a basal and ancestral trait, and land plants evolved from a single common ancestor that formed symbiotic associations with fungal partners before roots evolved. For at least the past 30 years, the prevailing paradigm has been that AM fungi are the ancestral form of all plant-fungal symbioses co-evolving with the earliest land plants. AM associations are the most common type of mycorrhiza, and are currently found in over 70% of land plant species including simple and complex thalloid liverworts. However, new evidence reported by members of the project team (MB, JGD, SP) has revealed that the most basal extant groups of liverworts, the Haplomitriopsida, exclusively form associations with the most basal group of plant-symbiotic fungi - the Endogonales. For the first time, we now have evidence pointing to the identity of the fungal group at the dawn of their nutritional symbiosis with land plants. This opens a remarkable new window for functional investigations into how the symbiosis facilitated the emergence of the terrestrial biosphere.
Our proposal exploits these findings by addressing three fundamental evolutionary questions relating to the initial phase of plants 'greening of the Earth': (1) Are the associations between liverworts and species of Endogone functionally equivalent to those formed with AM fungal partners? (2) Was the switching of fungal partners from facultatively saprotrophic Endogone to obligately biotrophic AM fungi through the evolutionary advance of basal liverworts driven by increasing mutualistic benefits to the plants and fungi? (3) Did the accumulation of soil organic matter favour obligately biotrophic AM fungi over facultatively saprotrophic Endogone in supplying mineral nutrients to the plants?
We have carefully selected 7 liverwort species with fungal associations that provide a powerful spectrum of model systems amenable to experimentation and quantitative functional analyses of C exchange, nutrient relationships and fungal specificity. All of our target organisms can all be cultured either from spores or gemmae to provide plants with and without fungal symbionts. This provides a robust approach for enabling quantification of fungal colonization on gametophyte growth, nutrition and reproductive output within a 3 yr project. Our experimental programme will be conducted on (1) mature field-collected populations and (2) symbiotic vs. asymbiotic plants grown from gemmae/spores. Field collected populations will be used for functional studies of C-allocation from liverworts to their fungal partners and reciprocal uptake of nutrients into the plants via the fungi. Populations from gemmae/spores will be used for investigating the net costs/benefits of the fungal symbionts on the growth and reproductive output of the liverworts and the biomass and extent of the fungal partners. Molecular identification and ultra-structural studies will be undertaken on both sets of plants to establish the identity of the fungal endosymbionts, the nature of the plant-fungal interfaces, and how these relate to function and host specificity. Overall, this project will contribute fundamental knowledge and understanding to the dawn of an ancient symbiosis between land plants and fungi that played a founding role in the evolution of terrestrial ecosystems - a topic closely aligned to NERC's Earth System Science Theme high-level challenge "improving current knowledge of the interaction between the evolution of life and the Earth".

Who will benefit beyond other academics ?

(1) 'Next generation of reseachers' in schools
(2) General public
(3) Key stakeholders from the industrial sector

We have identified 5 specific activities pathways for reaching these groups:

(1) Dedicated Website written in clear easily accessible language. The website will serve as a link to the institution websites of the PI (APS) and Co-Is (Kew Gardens and the Natural History Museum) and to other websites that discuss plant evolution. It will be regularly updated with postings describing new findings and forthcoming publications.
(2) Outreach activities in schools. We will engage the 'next generation' of researchers by undertaking visits to local schools in Sheffield and London and by hosting year 10 work experience placements. These visits will consist of talks and practical workshops to engage the students in discussions about symbiosis between organisms and its role in plant evolution throughout Earth's history.
(3) Summer Internships. We routinely host Sixth Form students in our labs to provide potential scientists with direct experience in the scientific approach and methodology, and to illustrate what it is like to work in a research environment. We propose to host two such students (3 weeks each) over the duration of the project in Sheffield, Kew and the Natural History Museum, London.
(4) Outreach activities to the general public. The Natural History Museum and Royal Botanic Gardens-Kew (RBG) in London are world-leaders in public engagement in science. The NHM, which includes the £78 million landmark development of the Darwin Centre 2 (DC2), offers a unique and ideal platform for engaging with the public in a variety of ways. These include its Internet presence and opportunities to give talks to visitors in the David Attenborough Studio (within DC2), as part of the 'Nature Live Events'. We plan to include a specific 'Nature Live Event' on "A 400-million year-old symbiotic relationship: plants and fungi". RBG-Kew has an Evolution house with >1 million visitors a year. We are in discussions with key people to set-up a semi-permanent display for visitors there about the role of symbiotic fungi in land plant evolution. We plan to exploit these facilities further to communicate our science to the public by giving special lectures at 'Greening of the Earth' Road shows in addition to key museums and botanical gardens in England, Scotland and Wales. At each event, the PDRA will deliver an engaging talk highlighting the 'big science' question being addressed by the project and its wider relevance to society.
The PDRA and 1 PI/CoI will then participate in pre-arranged open discussion sessions. Flyers describing the aims and 'big science' question of the project will be distributed. We will liaise with the following organizations to organize the associated lecture and other activities. Key personnel from each organization have been contacted and are excited about the possibility of hosting these events.
(5) Industry forum. We will demonstrate the potential applications of our data and materials archives via an open day at Sheffield aimed at industry representatives. The PI/Co-I's have been involved in the highly successful 'Multi Functional Landscapes forum' held in Sheffield in 2010 with aimed to engage key stakeholders from industry policy. We will use our extensive network of industrial collaborators to invite key stakeholders (e.g. Corus-TATA steel, RAGT Seeds, Lindham Turf, Bonningale Nurseries) to the forum.

Milestones and measures of success. Key milestones will be: 1) public understanding of science engagement events (schools/Museums); 2) staging of an industry forum event in the final year; 3) creation of an interactive website. Components (1) and (2) will be evaluated via post-presentation feedback. Component (3) will be assessed by counting website hits.