Clock control of legume-rhizobia interactions

"The symbiotic relationship between legumes and soil rhizobia (nitrogen fixing bacteria) is a globally important process for the fixation of atmospheric nitrogen into ammonia. From this, biologically available nitrogen is introduced to soil in croplands across the globe. This process currently reduces the requirements for nitrogen fertilisers produced using the energy intensive Haber-Bosch process, which is estimated to use 1% of all global energy output. It is paramount that the symbiosis between the legume and rhizobia is fully understood to enable optimization and increase in the efficiency of the interaction, leading to reduction in requirements for nitrogen fertilisers.

The symbiosis involves a complex interplay of signalling between the bacteria and plant which is not fully understood. One component that affects the interaction is the circadian clock of the plant, based on recent new data which implicates the involvement of rhythmic leghaemoglobin's in the control of genes which are also expressed rhythmically coding for the nitrogenase enzyme which is responsible for the conversion of atmospheric nitrogen to ammonia. These leghaemoglobins are thought to be temporally coordinated by the circadian clock of the plant to optimise oxygen concentration in the nodule to induce nitrogenase gene expression. A greater understanding of this communication and control via the circadian clock control can lead to the development of legume crop lines with optimised clocks for their specific environment and rhizobial partner. This work will do this by modelling the expression of plant and rhizobial clock genes when plants experience different daylength cycles, followed by use of mathematical methods and network inference. Ultimately, the project seeks to use this information in an applied way to improve agricultural sustainability by reducing demand for nitrogen fertilizer inputs."