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Liam Walker

Nitrogen is an essential element for life; chiefly because it is required for amino acids and nucleotide bases. Although the most abudant element in the Earth's atmosphere, the majority of nitrogen on Earth is inaccessible to most organisms. This is because the triple bond of dinitrogen is very stable so nitrogen atoms can not easily be freed to react with other elements and form compounds.

The process of splitting dinitrogen and incorpration of nitrogen into forms usable by life is called nitrogen fixation. Natural phenomena such as lightning can fix nitrogen as well as artificial fixation by the Harber process. But the majority of nitrogen fixation is the work of nitrogen-fixing bacteria.

Nitrogen-fixing bacteria exist as both free-living bacteria and as symbionts with plants in a process called nodulation. For plants such a symbiosis if extremley valuable as it provides access to nitrogen containing compounds even if these are absent in the soil. Interactions between legumes and nitrogen-fixing Rhizobia represent the best characterised examples of such an interaction.

Industrial nitrogen fixation is responsible for providing nitrogen for fertilizer for use in agriculture but this comes at great environmental and monetary expense. If nodulation could be transferred to non-legumes such as cereal crops then the benefits to society would be unquantifiably enormous which huge benefits in areas such as food security and biofuels.

I work with legumes Lotus japonicus and Medicago truncatula and non-legumes Arabidopsis thaliana and Solanaum lycopersicum (tomato) to try to find differences in expression of miRNAs in response to pathogens and nitrogen-fixing symbiotic bacteria. miRNAs are thought to be responsible for up-regulation of nodulation at the expense of defence when leguminous plants respond to rhizobia. Ultimatley by understanding these differences we hope that we can make progress in transferring nodulation to non-legumes.