A comparative genomics examination of desiccation tolerance and sensitivity in two sister grass species.

Abstract

• Desiccation tolerance is an ancient and complex trait that spans all major lineages of life on earth. Although important in the evolution of land plants, the mechanisms that underlay this complex trait are poorly understood, especially for vegetative desiccation tolerance (VDT). The lack of suitable closely related plant models that offer a direct contrast between desiccation tolerance and sensitivity has hampered progress. We have assembled high-quality genomes for two closely related grasses, the desiccation-tolerant and the desiccation-sensitive . Both species are complex polyploids; is primarily tetraploid, and is primarily hexaploid. undergoes a major transcriptome remodeling event during initial exposure to dehydration, while has a muted early response, with peak remodeling during the transition between 1.5 and 1.0 grams of water (gH O) g dry weight (dw). Functionally, the dehydration transcriptome of is unrelated to that for . A comparative analysis of the transcriptomes of the hydrated controls for each species indicated that is transcriptionally primed for desiccation. Cross-species comparative analyses indicated that VDT likely evolved from reprogramming of desiccation tolerance mechanisms that evolved in seeds and that the tolerance mechanism of represents a recent evolution for VDT within the Chloridoideae. Orthogroup analyses of the significantly differentially abundant transcripts reconfirmed our present understanding of the response to dehydration, including the lack of an induction of senescence in resurrection angiosperms. The data also suggest that failure to maintain protein structure during dehydration is likely critical in rendering a plant desiccation sensitive.