The Genetic Architecture of Shoot and Root Trait Divergence Between Upland and Lowland Ecotypes of a Perennial Grass

Recent climate trends are driving rapid shifts in global precipitation patterns, leading to changes in soil water availability that can impact plant performance and distribution. Soil water availability is an especially important driver of contemporary evolution and ecotype formation in plant populations. In the process of ecotype formation, populations can diverge across many traits and exhibit different niche characteristics, which requires coordination between plant organ systems. For instance, although plant water loss is largely governed by shoot systems, root systems determine water access and constrain shoot water status. Understanding the genetic architecture of root traits and their relationship with shoot traits helps to develops a more complete picture of the adaptive differences that arise between ecotypes in response to changes in water availability. P. hallii is an emerging model system for C4 perennial grasses, including the important biofuel crop switchgrass (P. virgatum). Here, we produced an intercross between individuals of the xeric and mesic ecotypes of Panicum hallii, utilized a single seed decent method to generate a population of recombinant inbred lines at the F₇ generation and subsequently constructed a new genetic map based on whole genome re-sequencing. Utilizing extensive phenotyping of root and shoot traits and a quantitative genetic approach, we identified several genomic ‘hotspots’ which control suites of correlated root and shoot traits, thus indicating genetic coordination between plant organ systems in the process of ecotypic divergence. In addition, we found that genomic regions of colocalized QTL for the majority of shoot and root growth related traits were independent of colocalized QTL for shoot and root resource acquisition traits. Finally, we confirmed major finding from the greenhouse in a field setting. Future research will focus on the impact of P. hallii native soil microbiomes on root traits and plant performance in a P. hallii mapping population.