Unravelling the diversity and function of fine root endophytes

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Plants interact with diverse communities of microbes, which constitute their microbiome, and which have major impacts on their growth and development. In most ecosystems the microbiome is dominated by mycorrhizal symbioses, in which the plant provides the fungus with sugars and lipids in exchange for nutrients assimilated by the fungus from the soil. The most widespread mycorrhizal symbiosis is the arbuscular (AM) type, which is recognized as a key determinant of ecosystem processes, through its role in biogeochemical cycling and in supporting the diversity and productivity of plant communities. Until recently, it was assumed that the fungi which form AM comprise the phylum Glomeromycota, and our understanding of the ecosystem roles of AM is based almost exclusively on this group of fungi. However we have recently shown that fungi which form the distinctive 'fine root endophyte (FRE)' AM morphotype are members of the Order Endogonales within the phylum Mucoromycota so that the AM symbiosis is actually formed by two distinct groups of fungi which diverged over 700 million years ago.Although we know that FREs are globally distributed and can be abundant within ecosystems we know almost nothing about the diversity, ecology or ecosystem function of the fungi involved. However, evidence suggests that FRE and Glomeromycota have contrasting interactions with the environment and may perform different functional roles in ecosystems. In this project we will use existing DNA archives collected as part of the NERC Countryside Survey to determine the diversity and abundance of FREs across major British habitat types, and compare the environmental, vegetation and climatic factors which determine distribution of FREs and Glomeromycota. Currently FRE are 'dark fungi' known only as environmental sequences. Our research suggests that FREs represent multiple species, and we will collaborate with Australian and Swedish researchers to define these based on both their genetics and morphology, and determine the extent to which these have global distribution patterns. We have evidence to suggest that FREs and glomeromycota have different interactions with soil phosphorus, with FREs more abundant under conditions of very low phosphorus availability. We will collaborate with Irish researchers to investigate how soil phosphorus status affects diversity and abundance of FREs using a unique 50 year pasture experiment in Wexford. We will establish whether FREs function as mutualistic symbionts which promote plant growth and nutrient supply, similar to the interactions that Glomeromycota have with their host plants. A key part of the programme will be to assemble genomes of FREs and use these to understand the functional roles of FREs in ecosystems, and the interactions which determine their distribution across ecosystems. Since FREs can't be grown in the absence of plants, or under pure culture conditions, we will take advantage of emerging long read DNA sequencing technology which now opens the exciting possibility of assembling FRE genomes directly from DNA extracted from environmental metagenomes.In addition to providing fundamental understanding of the diversity and function of the AM formed by FREs, we will provide technological advances which will facilitate a major advance in our ability to characterise the function and ecological significance of microbial eukaryotes such as fungi and protists, which are largely unculturable and have been neglected in environmental genome sequencing efforts to date.