Periodic Reporting for period 2 - MYCOREV (A Mycorrhizal Revolution: The role of diverse symbiotic fungi in modern terrestrial ecosystems)
Período documentado: 2022-03-01 hasta 2023-08-31
The colonization of land by plants over 500 million years ago was a significant event in Earth's history, leading to the establishment of land flora that transformed the biosphere and atmosphere. However, to access the mineral nutrients essential for growth and proliferation, early rootless plants needed to form intimate relationships with symbiotic arbuscular mycorrhizal fungi (AMF) that liberated and transferred nutrients from rocks to the plant in exchange for carbon fixed through photosynthesis. Recent discoveries challenge the traditional view that AMF played the primary role in facilitating the colonization of Earth's landmasses by plants. Instead, the Mucoromycotina "fine root endophyte" (MFRE) fungi, which are taxonomically distinct from AMF, may have also played a critical role in this process.
Recent findings demonstrate that symbiosis with MFRE is not limited to early diverging plant lineages, but is present in plants spanning the entire land plant phylogeny. However, the precise host range of MFRE symbionts remains unknown, which limits our understanding of the significance of MFRE in ecosystem structure and function. The most recent findings show that MFRE symbioses are functionally distinct from AMF symbioses in terms of the nutrients supplied to their hosts and their responses to changing atmospheric CO2 concentrations. These discoveries challenge much of what we thought we knew about plant-fungal symbioses, and the fundamental biology of MFRE-plant symbioses remains largely unknown.
MYCOREV aims to address these critical knowledge gaps regarding the diversity, structure, and functional significance of plant-MFRE symbioses. By testing the overarching hypothesis that "MFRE play a major role in plant nutrition and nutrient cycling in modern terrestrial ecosystems," this project will pave the way for a revolution in mycorrhizal research in the 21st century. Understanding the complexity of plant-fungal symbioses and their responses to environmental change is essential for regulating plant communities, ecosystem structure and function, climate, and sustainable agriculture now and in the future. The project is based on three key objectives:
OBJ 1: Determine identity, frequency, diversity, host range and relatedness of MFRE in plants across phylogenetic, developmental and ecological gradients.
OBJ 2: Define diagnostic ultrastructure in MFRE vs. AMF symbiotic interfaces and characterise the spatial distribution of each symbiont in planta in single and dual fungal colonisations in multiple plant species and determine how they are affected by changes in atmospheric CO2 relevant to future predicted changes.
OBJ 3: Quantify functional differences between MFRE- and AMF-plant symbioses in terms of carbon and nutrient fluxes between fungi and host plants in single and dual colonisations across a range of organic and inorganic nutrient sources in terms of type, quantity, metabolism and temporal dynamics of resource exchange and how these are affected by changes in atmospheric CO2.
Recent findings demonstrate that symbiosis with MFRE is not limited to early diverging plant lineages, but is present in plants spanning the entire land plant phylogeny. However, the precise host range of MFRE symbionts remains unknown, which limits our understanding of the significance of MFRE in ecosystem structure and function. The most recent findings show that MFRE symbioses are functionally distinct from AMF symbioses in terms of the nutrients supplied to their hosts and their responses to changing atmospheric CO2 concentrations. These discoveries challenge much of what we thought we knew about plant-fungal symbioses, and the fundamental biology of MFRE-plant symbioses remains largely unknown.
MYCOREV aims to address these critical knowledge gaps regarding the diversity, structure, and functional significance of plant-MFRE symbioses. By testing the overarching hypothesis that "MFRE play a major role in plant nutrition and nutrient cycling in modern terrestrial ecosystems," this project will pave the way for a revolution in mycorrhizal research in the 21st century. Understanding the complexity of plant-fungal symbioses and their responses to environmental change is essential for regulating plant communities, ecosystem structure and function, climate, and sustainable agriculture now and in the future. The project is based on three key objectives:
OBJ 1: Determine identity, frequency, diversity, host range and relatedness of MFRE in plants across phylogenetic, developmental and ecological gradients.
OBJ 2: Define diagnostic ultrastructure in MFRE vs. AMF symbiotic interfaces and characterise the spatial distribution of each symbiont in planta in single and dual fungal colonisations in multiple plant species and determine how they are affected by changes in atmospheric CO2 relevant to future predicted changes.
OBJ 3: Quantify functional differences between MFRE- and AMF-plant symbioses in terms of carbon and nutrient fluxes between fungi and host plants in single and dual colonisations across a range of organic and inorganic nutrient sources in terms of type, quantity, metabolism and temporal dynamics of resource exchange and how these are affected by changes in atmospheric CO2.
Activities within WP1 have aimed to study the natural distribution and diversity of Mucoromycotina ‘fine root endophytes (MFRE). We used a nested sampling strategy to collect 1600 root and soil samples from multiple sites of contrasting habitats and environmental gradients across the Peak District National Park. We selected six plant species based on their different lineages and ubiquity across UK and wider Europe, and all were found via microscopy to be hosts of MFRE, often in co-colonisation with arbuscular mycorrhizal fungi (AMF). We're currently processing the samples for DNA extraction and sequencing to determine MFRE community composition and assess host specificity across the range of habitats sampled.
In WP2, we isolated MFRE from the gametophytes of Lycopodiella inundata, which was used to colonize the roots of white clover seedlings in vitro. We have since obtained a second isolate, Lyc-2, from the roots of L. inundata, and are attempting to isolate more from other plant species and directly from soil samples. We have also established in vitro microcosms using axenic seedlings of Trifolium repens and Plantago lanceolata with the MFRE isolates alone or with AMF. We're also testing the suitability of root-organ cultures for MFRE propagation and developing alternative methodologies for in vitro microcosms.
In WP3, carbon-for-nutrient exchange isotope tracing experiments using monoxenic cultures of MFRE and T. repens have showed direct exchange of carbon for nutrients. We have conducted similar experiments on Ranunculus acris with MFRE, AMF, and dual-inoculated treatments in a soil-based system. We have established inoculation of plants in soil-based systems with up to 70% root length colonization by MFRE and the exclusion of AMF. We have shown that the composition of fungal symbionts in buttercup roots affects plant biomass, and that MFRE transfer phosphorus and nitrogen to buttercups. We have also found that MFRE symbioses are CO2 responsive in buttercups and demonstrated functional complementarity between AMF and MFRE.
In WP2, we isolated MFRE from the gametophytes of Lycopodiella inundata, which was used to colonize the roots of white clover seedlings in vitro. We have since obtained a second isolate, Lyc-2, from the roots of L. inundata, and are attempting to isolate more from other plant species and directly from soil samples. We have also established in vitro microcosms using axenic seedlings of Trifolium repens and Plantago lanceolata with the MFRE isolates alone or with AMF. We're also testing the suitability of root-organ cultures for MFRE propagation and developing alternative methodologies for in vitro microcosms.
In WP3, carbon-for-nutrient exchange isotope tracing experiments using monoxenic cultures of MFRE and T. repens have showed direct exchange of carbon for nutrients. We have conducted similar experiments on Ranunculus acris with MFRE, AMF, and dual-inoculated treatments in a soil-based system. We have established inoculation of plants in soil-based systems with up to 70% root length colonization by MFRE and the exclusion of AMF. We have shown that the composition of fungal symbionts in buttercup roots affects plant biomass, and that MFRE transfer phosphorus and nitrogen to buttercups. We have also found that MFRE symbioses are CO2 responsive in buttercups and demonstrated functional complementarity between AMF and MFRE.
Through progress on MYCOREV to date, the project team have made some truly ground-breaking discoveries that have exceeded our own expectations. We have established a novel monoxenic culture system for MFRE-host plants, which has opened up the research field and allowed for more experiments than ever before. We have also found that the host specificity of the isolated MFRE strain Lyc-1 is much lower than previously thought, which means they can colonize many different plant species with the fungus and establish mutualistic interactions.
This exciting breakthrough could mean that MFRE uses a completely different colonization mechanism than other mycorrhizal fungi, which opens up new possibilities for plants to acquire beneficial symbionts. Furthermore, the MYCOREV team has discovered that the establishment of the symbiosis may not entirely depend on plant photosynthate transfer, which is a fascinating development from an evolutionary standpoint.
We have recently isolated a second MFRE strain. It will be critical to establish whether this strain has a similar breadth of potential host plant range or whether it is more specific, whether its functionality is similar or different to our first strain, and how closely related the two strains are. These exciting research directions are all being explored through the MYCOREV project, pushing the boundaries of mycorrhizal research and bringing wider attention to an incredibly understudied group of symbiotic fungi.
This exciting breakthrough could mean that MFRE uses a completely different colonization mechanism than other mycorrhizal fungi, which opens up new possibilities for plants to acquire beneficial symbionts. Furthermore, the MYCOREV team has discovered that the establishment of the symbiosis may not entirely depend on plant photosynthate transfer, which is a fascinating development from an evolutionary standpoint.
We have recently isolated a second MFRE strain. It will be critical to establish whether this strain has a similar breadth of potential host plant range or whether it is more specific, whether its functionality is similar or different to our first strain, and how closely related the two strains are. These exciting research directions are all being explored through the MYCOREV project, pushing the boundaries of mycorrhizal research and bringing wider attention to an incredibly understudied group of symbiotic fungi.