LAUSR

Abstract Droughts have a major impact on plant growth, limit global net primary production and are predicted to increase in the course of climate change. Knowledge of the plant drought response on a molecular level can facilitate the selection of drought resistant genotypes and genetic engineering and thereby support strategies to preserve natural and agricultural vegetation against drought stress. Since species from the genus Panicum are naturally adapted to varying degrees of drought, they are perfectly suited for comparative studies of the plant drought response. To shed light on the molecular mechanisms of the drought stress response in the genus Panicum, three species that differ in their drought tolerance, P. bisulcatum, P. laetum and P. turgidum were exposed to severe drought stress and subsequent recovery. An RNA-Seq was conducted and de novo transcript assemblies were generated. Differential gene expression analyses revealed 108 genes that are upregulated upon drought stress in all three species, as well as 179 genes that were found consistently downregulated. 35 commonly upregulated and 69 commonly downregulated genes were assigned to a regulatory role in the drought response, while 43 commonly upregulated and 77 commonly downregulated genes were assigned to a functional role. The assigned functions and pathways comprise, among others, abscisic acid (ABA) synthesis, signal transduction, osmolyte synthesis, protection of macromolecules, cell wall and cuticle remodeling and drought-induced dormancy. Some of the functionally annotated orthologs have not been reported to be drought responsive yet, among them an oil body associated gene (OBAP2B), a chaperone from endoplasmic reticulum (BCAP31-like) and 30 commonly upregulated and 33 commonly downregulated orthologs with unknown function. Additionally, 150 genes were identified, that were found to be upregulated in the more drought tolerant P. laetum and P. turgidum but not in the more drought sensitive P. bisulcatum and therefore might contribute to their higher drought tolerance.