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Extracellular proteins released by plant roots contribute to nutrient mobilisation from organic matter, pathogen defence and localised root growth adjustment to the surrounding environment. Thereby, they have the potential to remodel the extracellular matrix and play a pivotal role in plant nutrition and survival. However, little is known about the composition, abundance and functional potential of the extracellular proteome derived from plant roots at the plant-soil interface under nutrient stress conditions. In this project, we apply both untargeted and targeted proteomics approaches to characterise the localised response of wheat root tips and the associated extracellular proteome to low phosphate conditions. By using untargeted LC-MS/MS techniques, we first established a comprehensive map of the proteins released by wheat roots. More than 300 proteins were identified within the extracellular space. Relative to the root tip proteome, the proteome present in this environment was significantly enriched in proteins with predicted secretion tags and apoplastic localisation. The majority of proteins had a functional annotation related to stress and pathogen response, protein processing and cell wall biosynthesis. Second, we developed multiple reaction monitoring (MRM) assays for the detection of root-released phosphatases and other phosphate starvation responsive proteins within the extracellular space. Ultimately, the delineation of the wheat root tip and extracellular proteome responses to phosphorus starvation by targeted proteomics will deepen our understanding of spatial and time resolved phosphorus dynamics at the plant-soil interface. |