Intertwined signatures of desiccation and drought tolerance in grasses

Grasses are among the most resilient plants and some can survive prolonged desiccation in semi-arid regions with seasonal rainfall. This vegetative desiccation tolerance has arisen independently multiple times within the grass family, but the genetic elements that differentiate desiccation tolerant and sensitive grasses are largely unknown. Here we leveraged comparative genomic approaches with the resurrection grass Eragrostis nindensis and the closely related desiccation sensitive cereal Eragrostis tef to identify changes underlying desiccation tolerance. We extended the analyses to include the grasses maize, sorghum, rice, and the model desiccation tolerant grass Oropetium thomaeum to identify broader evolutionary conservation and divergence. We identified changes in chromatin architecture and expression dynamics related to desiccation in E. nindensis. It was previously hypothesized that transcriptional re-wiring of seed desiccation pathways confers vegetative desiccation tolerance. We demonstrate that the majority of seed dehydration related genes show similar expression patterns in leaves of desiccation tolerant and sensitive species during dehydration. However, we discovered a small set of orthologs with expression specific to leaves of desiccation tolerant species, and seeds of sensitive species. This supports a nuanced role of seed-related genes where many overlap with typical drought responses but some crucial genes are desiccation specific in resurrection plants.