Identification of Differential Physiological and Molecular Responses in Tolerant and Sensitive Switchgrass Cultivars during Drought Stress.

Switchgrass (Panicum virgatum) is a native North American perennial grass, and a target species for biofuel feedstock production based on its high biomass. Switchgrass has two ecotypes, upland and lowland, based on phenotype and adaptation to distinct habitats. In this study, we screened drought stress response of forty-nine switchgrass cultivars from both lowland and upland ecotypes by assessing physiological parameters, and metabolites (hormones, polyamines, amino acids, and nonstructural carbohydrates). The results revealed significant phenotypic variation in switchgrass under control condition as well as drought stress. Based on the phenotypic screening results, we chose lowland Alamo and upland Dacotah as drought-stress tolerant and sensitive cultivars, respectively, for further study. The two cultivars were subjected to well-watered and drought stress treatments for 30 days.  The results indicated that drought tolerant Alamo had greater photosynthetic rate, and stomatal conductance. RNA-seq analysis was also performed using leaf tissues. Differentially expressed genes were identified, among which co-expressed genes were discovered using network analysis. The identification of genes associated with drought stress tolerance and sensitivity will help us understand the mechanism of stress response in switchgrass and eventually help improve biomass production in switchgrass.