Approximately 75% of the nitrogen present in a plant is in the leaf chloroplasts. Chloroplast degradation for recycling is a major nitrogen source for supporting new growth. Nitrogen is essential for plant growth and one of the most expensive and polluting fertilizers. Understanding the cellular pathways that mediate nitrogen recycling and remobilization in leaves is of crucial importance for the sustainable production of bioenergy crops. Our goal is to understand how two different photosynthetic cell types within a C4 leaf, mesophyll and bundle sheath cells, degrade and recycle cellular components, including chloroplasts, under low nitrogen conditions using single-cell and spatial multi-omics approaches. In C4 species like maize, M and BS cells work in coordination to maximize atmospheric CO2 fixation through photosynthesis. The two cell types have structurally and functionally different chloroplasts and differ greatly in their metabolic activities. We will analyze how to major recycling pathways (canonical autophagy and the newly discovered Nbr1- compensatory pathway) are regulated and coordinated to allow C4 grasses to maximize nutrient utilization and recycling as well as to minimize cellular stress.
Our specific aims are:
(1) To dissect how canonical autophagy and compensatory pathways impact cellular recycling in differentiating, mature, and senescing photosynthetic maize leaf cell types under N deficiency using a suite of single cell/spatially resolved omics approaches (proteomics, transcriptomics, and metabolomics).
(2) To analyze the protein profiles of individual chloroplasts targeted by either autophagy and compensatory pathways using fluorescent reporters and nanoPOTS proteomics.
This project will provide fundamental knowledge to enable sustainable production of cost-competitive bioenergy C4 crops, by better understanding nutrient recycling to increase yields in low nutrient soils while minimizing fertilizer requirements and pollution.