Regulation of nutrient-stress signaling through the plant vascular system

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Application of nitrogen/phosphorous/potassium fertilizers enables us to achieve enhanced productivity in agriculture. Modern breeding program has sought to develop crop species to increase nutrient use efficiency for achieving sustainable crop yield and ensuring global food security under reduced/limited fertilizer inputs. Once plants face limitations in mineral nutrient availability, roots are usually the first tissues to respond to these stress conditions which are sensed by root-localized mechanisms; the root translates these stresses into the root-derived signals that are transported through the xylem to communicate the challenging conditions to the shoot. Delivery of these signals to vegetative tissues elicits production of specific output signals that enter the phloem to carry commands from the shoot, back to the root, to integrate the requirements for developmental and physiological processes. Although there is clear evidence in the literature that the plant vascular system functions as the effective communication pathway, much remains to be discovered in terms of the signaling components in these pathways and how they function in mineral nutrient homeostasis. The long-term goal of my research program is to verify molecular regulatory mechanisms in nutrient-stress signaling, mediated by the root-shoot communication through the plant vascular system, especially the phloem. To advance the knowledge of the phloem function in long-distance nutrient-stress signaling, I outline here a strategy to identify regulatory mechanisms involved in integrating nutrient homeostasis by phloem-mediated long-distance signaling molecules. Limited information is available on the role of phloem mobile molecules in nutrient-stress signaling, and the utilization of functional genomics, bioinformatics, physiological and protein biochemistry studies will be involved to address the following objectives: 1) Determine which nutrient-stress responsive phloem proteins traffic to the root and shoot apex, 2) Characterize mobile transcription factors which function in gene regulatory pathways at the sites the signals are delivered to responsive sink tissues, 3) Validate the role of these identified phloem-mobile signaling molecules in plant developmental adaptive responses to nutrient-stress conditions. The studies described in this proposal will provide increased understanding and new insights into molecular regulatory mechanisms that serve in nutrient uptake and utilization in plants, mediated by phloem-based systems. This knowledge would offer potential gene targets and a basis for breeding programs aimed at enhancing nutrient use efficiency in crop plants.