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 <i>Sporobolus stapfianus</i> and the desiccation-sensitive <i>Sporobolus pyramidalis</i> Both species are complex polyploids; <i>S. stapfianus</i> is primarily tetraploid, and <i>S. pyramidalis</i> is primarily hexaploid. <i>S. pyramidalis</i> undergoes a major transcriptome remodeling event during initial exposure to dehydration, while <i>S. stapfianus</i> has a muted early response, with peak remodeling during the transition between 1.5 and 1.0 grams of water (gH₂O) g^-1 dry weight (dw). Functionally, the dehydration transcriptome of <i>S. stapfianus</i> is unrelated to that for <i>S. pyramidalis</i> A comparative analysis of the transcriptomes of the hydrated controls for each species indicated that <i>S. stapfianus</i> 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 <i>S. stapfianus</i> 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.