Physiological Controls of Root Growth Maintenance under Water Deficits: Contrasting Responses of Maize Lateral and Nodal Roots

The growth of roots determines root system architecture and exploration of the soil profile, and is a critical component of plant adaptation to water-limiting conditions. This presentation will focus on the maintenance of growth in drying soil in both lateral roots, which are vital to mine the soil for water, and the stem-borne nodal roots, which are essential for development of the mature root system in maize and other grasses. In both root types, the physiological controls that determine growth maintenance at low water potentials are poorly understood. Recent progress will be reviewed, using both model system approaches and extending to drought conditions in the field. Studies of two maize cultivars, FR697 and B73, with divergent responses of both lateral and nodal root growth to water deficits revealed contrasting mechanisms of growth maintenance in the two root types. In lateral roots, the results showed large genotypic variability in the interaction of water deficit with the developmental determinacy program, which was unaffected in B73 but delayed in FR697 under mild water deficits, thereby resulting in maintenance of root elongation. For nodal root studies, a divided-chamber system was developed to characterize growth responses to precise variations in soil water potential. Results showed substantial differences in growth sensitivity both between the genotypes and between roots from different nodes, and highlight the importance of hydraulic properties that determine the relation between root growth zone and soil water status. To investigate how nodal roots respond metabolically to water deficits, current studies are focused on multi-omics (transcriptome, plasma membrane proteome, metabolome) profiling within the root growth zone under both lab and field conditions. This knowledge will build a foundation for the long-term goal of developing innovative approaches to improve water capture and crop productivity under water-limiting conditions. Supported by NSF Plant Genome Program grant no. 1444448.