Defining the symbiotic calcium channel of legumes

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Cells have the capacity to recognise a wide array of signalling molecules and such recognition is essential to allow coordinated development in multicellular organisms. Calcium is commonly used as a secondary messenger that allows the recognition of a signal, for instance on the cell surface, to be transmitted to other regions of the cell, for instance the nucleus where gene regulation occurs. The potency of calcium as a signalling molecule and the fact that sustained calcium levels in the cytoplasm are toxic, means that calcium levels are tightly regulated. Calcium is either pumped outside the cell or into intracellular compartments such as the endoplasmic reticulum, the vacuole and vesicles. The release of calcium into the cytosol to act in signalling is the function of calcium channels that reside on the membranes of these compartments and allow the flow of calcium with its concentration gradient into the cytoplasm or nucleoplasm. Proteins that function as calcium channels have been extensively studied in animal systems and a number of channel complexes have been shown to regulate calcium. Many of the animal calcium channels are absent in plants and this has hindered the characterisation of calcium signalling in plant systems. The proteins responsible for regulation of calcium in plant cells are only just beginning to be discovered. In this proposal we will define the calcium channels responsible for calcium oscillations that occur in the symbiosis signalling pathway of legumes. This signalling pathway is responsible for the establishment of nitrogen-fixing bacterial associations as well as beneficial fungal associations that occur in legume roots. We have already identified a strong candidate for the symbiotic calcium channel and in this proposal we will further validate the role of this candidate calcium channel in symbiosis signalling, as well as define the components of the channel complex that is likely to reside on the nuclear membranes.