Mapping QTL for Root System Architecture Traits in Brachypodium distachyon Under Nutrient Limitation using RootXpose, a High-Throughput Imaging and Analysis Platform

Plant root system architecture (RSA) describes the number and location of roots of a plant at any given moment during development.  RSA is plastic and dynamic, allowing plants to optimize the placement of roots in soil to acquire the water and nutrients required for growth.  Unfortunately, RSA is also notoriously difficult to visualize in soil, and removing plants from soil destroys most RSA characteristics.  This phenotyping bottleneck has stymied the discovery of genes that control RSA, particularly among important monocot species.  To overcome this challenge, we have developed RootXpose, a root phenotyping platform that permits high-throughput and non-destructive RSA imaging and analysis of plants grown on transparent gel media.  We have used RootXpose to identify quantitative trait loci (QTL) that control RSA traits under nitrogen and phosphorus limitation in a Brachypodium distachyon recombinant inbred line population.  Our current efforts are focused on validating the biological significance of the predicted QTL, and narrowing the QTL genomic intervals.  This work will set the stage for identifying the underlying causal polymorphisms, testing the functional significance of these RSA traits on plant growth under nutrient stress, and using this information to explore the regulation of RSA in monocot crops.