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With global population expected to reach 10 billion by 2050, agricultural productivity is increasingly important. Water is the number one limitation on agricultural yield world-wide. To meet the demands for food, fiber, and plant-based fuels, we must improve the ability of plants to reach and take up water. The uptake and acquisition of water is mediated by plant roots; therefore, we must understand the traits governing and contributing to root growth, particularly in the arid conditions that will likely characterize agriculture in the coming decades. The root system of grasses includes an embryonic root system, which supplies water during seedling establishment, and a system of stem-borne nodal roots, also referred to as "crown roots". In maize, nodal roots supply most of the water after seedling establishmentand deeper nodal root growth is a key adaptation to retrieve water in dry soil. Nodal roots are unique among plant organs for their capacity to maintain growth at water potentials (ψw) low enough to completely cease growth of other plant tissues. Deciphering the mechanisms that contribute to this incredible capacity for tissue expansion in dry environments will be crucial for plant breeding efforts aimed at improving drought tolerance.When growing in a low water potential environment, such as dry topsoil, continued root growth requires an increased concentration of carbon-based solutes, such as proline and sugars. Increased solute concentration helps expanding cells maintain turgor and expansive growth.To facilitate this, plants re-prioritize carbon resource allocation when experiencing water deficit (WD). Understanding the relationship between carbon supply, WD stressed roots, and how roots maintain growth is critically important for understanding plant responses to drought. Elucidating the physiological mechanisms that control this process will lead to major advances not just in maize, but potentially all cereal crops. Identifying the genes underlying these mechanisms will provide targets for future crop breeding efforts.This proposal will further develop my skills as a researcher and prepare me for a career leading research projects in industry, academic, or government research institutions. The major scientific goal is to develop a mechanistic understanding of how carbon partitioning in maize nodal roots relates to their ability to maintain growth during drought stress. Specifically, I will determine if increased carbon flux to the nodal root tip is required to maintain growth during WD, and if carbon partitioning to sink tissues changes in response to WD stress. I will also identify putative regulators of nodal root growth maintenance during drought stress using previously identified genes from an RNA-seq study. To test my hypotheses, I will address the following objectives:1) Characterize carbon flux to maize nodal roots during precisely-controlled drought regimes using a split-chamber growth system and isotopic 14CO2 radiotracer, and 2)Test the roles of genes identified by a drought stress RNA-seq experiment in nodal root growth and drought tolerance using genetic mutants.

Mccubbin, T.
University of Missouri - Columbia
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