Identification of two early acting plant genes in the mycorrhizal symbiosis

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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 is surprising since the developmental processes and gene expression profiles are quite different between these two symbioses, and hence specificity must be maintained. In support of this are nodulation specific receptor-like kinases that function upstream and nodulation specific transcriptional regulators downstream of the common signalling pathway. It is highly likely that there are mycorrhizal-specific components upstream and downstream of the common signalling pathway and there is evidence for additional signalling pathway(s) in the plant with specific role(s) in the mycorrhizal symbiosis. We have recently identified two loci that are specifically required for the mycorrhizal symbiosis. Mutations in these genes show a very early block in the mycorrhizal symbiosis: there is no sustained interaction between the fungus and the plant root. As far as we are able we have excluded a role for these loci in the production of a plant signal recognised by the fungus. Hence these loci are likely involved in the perception of a fungal signal(s) by the plant. In this proposal we will test this hypothesis as well as cloning these two genes. This work will provide crucial insights into the establishment of the mycorrhizal symbiosis and will provide an essential platform for defining the mechanisms underlying the specific recognition of the mycorrhizal fungus and appropriate induction of the developmental processes required for the accommodation of the fungal partner.

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