The Ancient Genome of an Aquatic Plant, Spirodela polyrhiza, at the Root of Monocot Evolution

Whole-genome sequencing has been critical in advancing our knowledge of the dynamics of ancient chromosomal rearrangements during speciation. Because of their agronomic significance the scientific community has given most attention to the family of species that contribute most to calorie production in the world, the grasses or gramineae. The grasses belong to the monocotyledonous division of flowering plants. To better understand the evolution of monocots, it has become necessary to sequence the genome of species outside the order of the Poales that comprises the gramineae. The Greater Duckweed or Spirodela polyrhiza, which had been sequenced by an international consortium (Nat. Commun. e3311), offers a unique perspective to study this evolution. As a member of the Alismatales, S. polyrhiza represents a well-preserved genome of a distant basal monocot. Developmentally and morphologically, Spirodela is very distinct from the gramineae, due to its aquatic, clonal lifestyle, and rare irregular flowering. This distinct genome therefore represents a strategic perspective to view traits that have been conserved through this phylogenetic distance, as well as those that have been altered for this distinct lifestyle.