MYC1 and MYC2 are required for early ....

Project: Research project (funded)Research

Project Details


Legumes form mutualistic symbiotic interactions with nitrogen fixing rhizobial bacteria and with arbuscular mycorrhizal fungi. These symbioses play crucial roles in sustainable agriculture, allowing improvement of soil fertility without artificial fertiliser application, growth of crop plants in nutrient poor environments and greatly benefiting the water use efficiency of crops. A conserved signalling pathway in legumes is required for the establishment of both the rhizobial and mycorrhizal symbioses. This project aimed to find plant genes that are required specifically in mycorrhizal symbiosis, independent of rhizobial symbiosis. Therefore, we proposed to analyse mutant plants that were unable to support a successful mycorrhizal symbiosis, to identify the mutated genes and subsequently study in detail their role in symbiosis.

Layman's description

Most plants form an interaction with mycorrhizal fungi that invade the plant root and grow through the soil and help the plant take up nutrients particularly phosphates. Furthermore, a selection of plant species, particularly legumes (peas and beans), have evolved an interaction with nitrogen fixing bacteria that convert atmospheric nitrogen into a form readily available to the plant. The mycorrhizal fungi and nitrogen fixing bacterial interactions are beneficial to both the plant and the micro-organism: the plant receives the nutrients nitrogen and phosphate in exchange for sugars generated through photosynthesis. The co-evolution of the plant and the microbe has created complex interactions and in a number of cases the organisms can be entirely dependent upon the interaction for survival: for instance mycorrhizal fungi are unable to live in the absence of the plant host.
In order to establish these interactions there is extensive molecular communication between the plant and the micro-organism. Plants release chemical signals into the soil that are recognised by the appropriate fungi and bacteria. In turn the bacteria and fungi release chemical signals to the plant that induce the plant to activate the developmental processes required to accommodate the micro-organisms. There is a single molecular pathway in the plant that is required to recognise both the fungal and bacterial signals. This is surprising since the developmental processes that are induced in the plant by nitrogen fixing bacteria are very different to the developmental processes induced by the mycorrhizal fungi. Hence, despite this commonality in the early signalling pathways the plant must still be able to discriminate between the fungus and the bacteria.
We have identified two plant genes that are only required for the fungal interaction, but not for the rhizobial nitrogen-fixing interaction. In this proposal we aimed to test the exact role these genes play in the successful communication between fungus and plant. This work will help us understand how this important interaction is established and will aid us in understanding how the plant is able to discriminate between mycorrhizal fungi and nitrogen fixing bacteria.

Key findings

The majority of plant species maintains an intimate relationship with microbes. Symbiosis with arbuscular mycorrhizal fungi (AMF) permits the plant to access nutrients that are in limited supply. We have isolated Medicago mutants that are no longer good hosts to AMF. We have characterised two of these mutants in detail. This led to the discovery of unexpected mechanisms that affect the development of the symbiosis or its function.
For example, we showed that molecules required in the synthesis of plant surface polymers (cutin), are involved in controlling the entry of the fungi into the root. Surprisingly, when the production of these molecules is disrupted, access is denied not only to the friendly AMFs, but also to a devastating pathogen. This work opens an entirely new field of research related to the question how plants distinguish beneficial from parasitic symbionts.
Another mutant lacks a key transcriptional regulator which is required specifically in mycorrhizal signalling and in distinguishing fungal from bacterial symbiosis. This is one of the first genes identified with a specific role in mycorrhiza formation.
Effective start/end date1/10/0630/09/09