Gene Expression and Physiological Differences in Neo-Octoploid Switchgrass Subjected to Drought Stress

Switchgrass (Panicum virgatum L.) has been subject to breeding to improve its yield and composition for bioenergy. Increased tolerance of environmental stress is another factor that can improve yields over the life span of a field plot. Natural ploidy series act as somewhat distinct gene pools in switchgrass that maintain differences with respect to tolerance of environmental stress and which can only be bridged through whole genome reduction or duplication events. In order to document potential wide-ranging effects of whole genome duplication, we examined the effects of water stress on growth, physiology, and gene expression in individual tetraploid clones of the switchgrass cultivar “Liberty” as well as neo-octoploid lines derived from it. The neo-octoploids behaved similarly to Liberty under water stress and recovery conditions: Water-stressed plants had approximately 50% or greater reduction of biomass, plant height, and node numbers. Tiller number and photosynthesis rates of stressed plants were reduced by up to 50%, while proline levels were significantly higher in stressed plants than well-watered plants. A total of 6134 differentially expressed genes (8% of the annotated genes with detectable expression in crown tissue) were detected under water-deficit stress, while 3310 differentially expressed genes were detected in crown tissue after 1 week of recovery from water-deficit stress relative to well-watered treatments. Only 187 genes were identified as being differentially expressed between 4x Liberty and its 8x derivatives. This study indicates neo-octoploids could be viable 8x-equivalent Liberty stand-ins for future breeding assays.