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Dr Leonie Luginbuehl and Professor Julian Hibberd


Brief Summary

The arbuscular mycorrhizal (AM) symbiosis is one of the oldest and most widespread symbioses on Earth. The symbiosis provides significant nutritional benefits to plants, however, it is also associated with a substantial carbon cost, as up to 20% of photosynthesis products are allocated to AM fungi. This project will explore the molecular mechanisms that regulate nutrient exchange in the AM symbiosis, with a particular focus on understanding how plants control carbon allocation to AM fungi.


Project Summary

The arbuscular mycorrhizal (AM) symbiosis is a mutualistic relationship that is formed by most land plants and AM fungi. This symbiosis provides significant benefits to both partners - plants receive water and essential mineral nutrients acquired by the fungal mycelium in the soil, and in return deliver photosynthetically fixed carbon to the fungus.

Plants that associate with AM fungi typically display enhanced mineral nutrition, improved growth, and increased yield. However, with up to 20% of the photosynthesis products being allocated to the fungus, the symbiosis is associated with a substantial carbon cost for the plant. A fundamental but unsolved question is how plants control nutrient exchange during the symbiosis.

This PhD project aims to explore the molecular mechanisms that allow plants to regulate the amount of fixed carbon allocated to AM fungi, and to identify which symbiotic, endogenous, and environmental factors affect this nutrient exchange.

We have previously identified a lipid biosynthesis and export pathway that transfers fixed carbon in the form of fatty acids from roots to fungal hyphae (Luginbuehl et al., 2017). This pathway is specifically active in root cortical cells that are colonized by the fungus.

The candidate will test how symbiotic, endogenous, and environmental factors regulate the activity of this pathway and thus carbon transfer to AM fungi. To this end, carbon will be traced under different conditions using carbon labelling techniques and reporter lines. The candidate will also explore how constitutive activation of this carbon transfer pathway affects plant physiology, nutrient exchange, and the outcome of the symbiosis. Finally, the candidate will use a transcriptomics approach to identify novel regulators of carbon transfer to AM fungi, and will test these candidates by analysing the extent of fungal colonization and nutrient exchange in overexpression lines and loss-of-function mutants.

To answer these questions, the candidate will work with the model plants Medicago truncatula and rice, for which all genetic resources are available.


What will the successful applicant do?

The candidate will learn a range of different plant molecular biology and physiology techniques, including cell-type and tissue-specific RNA-sequencing, cloning, carbon labelling, microscopy, plant transformation, and genome editing. In addition to wet lab techniques, the candidate will also gain experience in the computational analysis of gene expression data and statistics. Over the course of the PhD project, the candidate will develop skills in project management and scientific communication.