Transcriptomic Response of Maize Nodal Root Growth under Precisely Controlled Water Deficit

Drought is the number one limitation to agricultural productivity worldwide. Understanding the mechanisms that govern root growth responses to water deficits are critical to efforts to improve crop productivity under drought conditions. In maize, the stem-borne nodal roots perform the majority of water uptake after seedling establishment. Nodal roots are produced sequentially from the stem nodes and, under drought conditions, may have to grow through dry upper soil layers to reach water at depth. Despite early findings that nodal roots have a superior ability to continue elongation at low water potentials relative to other organs, the molecular controls that determine this ability remain poorly understood. In the present study, we utilized a model system that separates the seedling (primary and seminal) and nodal roots into distinct compartments, allowing for independent adjustment of water availability. This system mimics the situation in the field where upper soil layers dry and the continued growth of new nodal roots depends on water supplied via the stem base from already established roots. The system is highly robust, allowing for precise and repeatable nodal root growth kinetics over a range of defined soil water potentials. We used this system to profile transcriptomic changes of the growth zone of elongating nodal roots in response to water deficit. The project focuses on inbred line FR697, which exhibits a superior ability for nodal root growth maintenance under water deficit conditions. Our results indicate distinct responses of the meristematic, rapidly elongating, and decelerating regions of the growth zone that may govern the physiological adaptations that allow for maintenance of root growth during water deficit. The results will be integrated with proteomic and metabolomics analyses to develop a mechanistic understanding of the physiological genomics of maize nodal root growth under water stress. Supported by NSF Plant Genome Program grant no. 1444448.