Paszkowski Group: Harmonious co-existence: controlling mutualistic balance in arbuscular mycorrhizal symbiosis
Supervisor
Uta Paszkowski
Brief Summary
The plant symbiosis with arbuscular mycorrhizal (AM) fungi is as ancient as plant life on land, ubiquitously found across all plant lineages and globally driving ecosystem productivity today. Plants derive significant nutritional benefit form the interaction through enhanced supply with soil minerals
(particularly phosphate) by the fungus, which however comes at the cost of feeding the fungus with organic carbon. Genetic interference with either symbiotic phosphate uptake or carbon supply leads to a dysfunctional association. The mechanisms that ensure a cost-benefit equilibrium under natural fluctuating environmental conditions are currently unknown
Project Summary
We previously identified the Arbuscular Receptor-like Kinase (ARK) as required for the maintenance of AM symbioses across land plants since mutation of either the bryophyte (Marchantia paleacea) or the angiosperm (rice) ARK gene led to the loss of fungal fitness as reflected by the inability to complete its life-cycle1,2. Fungal vigour was restored when rice ark1 mutants expressed the bryophyte ARK gene from M. paleacea, corroborating functional conservation of ARK signalling from bryophytes to angiosperms. Importantly, reduced fungal fitness in ark1 could not be explained by dysfunctional carbon supply as arbuscule development and expression of symbiotic carbon efflux transporters was unperturbed3. ARK therefore governs the symbiotic equilibrium without directly regulating the dynamics of arbuscule development or nutrient exchange, and it does so across the plant kingdom from bryophytes to angiosperms. The M. paleacea genome contains one ARK gene while the rice ARK module consists of multiple components, namely the paralogous ARK2 and the Similar Protein to ARK1 (SPARK1), each of which are – similar to ARK1 - required for symbiosis sustenance but not for arbuscule development3, and unpublished. We hypothesise that the single M. paleacea ARK protein combines the functions of ARK1, ARK2 and SPARK1, consistent with the Rosetta Stone principle, which suggests that the rice proteins function together.
What will the successful applicant do?
To clarify the functional relationship of the rice proteins, and the evolutionary relationship to the ‘one protein scenario’ in M. paleacea, you will define the essential signalling domains and whether the rice proteins operate in a complex. You will provide insights into an ancient and strictly symbiosis-conserved mechanism that ensures mutualistic balance.