De novo Transcriptome Profiling of Two Edaphically and Phenotypically Divergent Grasses: Dominant Forage Grass Big Bluestem Andropogon gerardii and Drought-Tolerant Sand Bluestem Andropogon gerardii ssp. hallii

Andropogon gerardii big bluestem is a widespread forage grass that dominates loamy soils of the Great Plains, while sand bluestem ssp hallii, characterized by phenotypically distinct epicuticular waxes, is drought-adapted and restricted to sand dunes. We used RNA-seq to characterize the transcriptomes of these closely related, yet phenotypically divergent subspecies to understand drought tolerance. In sand bluestem, increased leaf reflectance and lower leaf temperatures are conferred by ß-diketone-rich epicuticular wax. Big bluestem, in contrast, has no detectable ß-diketones. Our goal is to construct and compare transcriptomes for sand and big bluestem to detect transcriptional differences in epicuticular wax synthesis. RNA was extracted from leaf tissues from two of the most phenotypically divergent sand and big bluestem individuals (greenhouse grown, common soil) and sequenced using Roche 454. We assembled big and sand bluestem transcriptomes using Newbler and miraEST. The miraEST assemblies have 34,661 and 36,470 contigs (N50=676, N50=678 for big and sand bluestem respectively). 421,874,106 additional 2x100bp paired end Illumina reads were obtained from four other individuals from each of the divergent populations. Illumina reads are being assembled with multiple values of k (21-61) using Velvet, Oases, and OasesMerge. These five assembles will be merged into a non-redundant consensus set using miraEST to reduce the number of assembler and sequencer-specific errors from the reference assembly. This resource will be a valuable tool for gene discovery and to assess transcriptional differences between these two divergent subspecies. Ultimately, we intend to probe the genetic basis of drought-adapted epicuticular waxes in sand bluestem.