Pan-grass synteny

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Phylogeny of evolutionary relationships of sequenced grass genomes. Radiation of grass family, poaceae is dated to have occurred 50-70 million years ago (MYA), following the shared ancient whole genome duplication of the grasses. Soon after the Panicoideae (Maize-Sorghum) and Ehrhartoideae (Rice-Brachypodium) clades diverged, Rice (Oryza sativa) and Brachypodium (Brachypodium distachyon) diverged (~49MYA). Maize/Corn (Zea mays) and Sorghum (Sorghum bicolor) diverged ~11MYA, followed by a whole genome duplication in the lineage of Maize. Red stars indicate whole genome duplications.
Expanded genome phylogeny of sequenced grass genomes. As a result of the whole genome duplication in the common ancestor of grasses and the maize specific whole genome duplication, there are effectively 10 genomes contained within the 4 sequenced grass genomes: 2xBd, 2xOs, 2xSb, 4xZm. A whole genome duplication events creates duplicate copies of every chromosome and all the underlying genomic features and genes. However, over evolutionary time, many duplicated genes are lost from one homeologous region or its partner through a process known as fractionation. Red stars indicate whole genome duplications.

The grasses, a family of plants known as the poaceae, can trace their lineages back to a common ancestor that probably lived between 50-70 million years ago, either right before or soon after the extinction of the dinosaurs(dinosaurs didn't eat grass). Since their emergence in the fossil record, the grasses have been extraordinarily successful, becoming one of the largest families of plants on the planet and covering vast swaths of the planet in the form of prairies/savannahs/steppes.

Grasses play a particularly important role in supporting human civilization as either three (rice, wheat, and corn/maize) or four (the same three plus sugar cane) grass species provide more than half of all the calories that feed the worlds population[1], and are the focus of much applied and basic scientific research.

Because of the comparatively recent radiation of the grass species[2], it was possible for us to use synteny to identify genes and genetic regions in grasses with sequenced genomes that are all related by common descent from a single ancestral sequence in the common ancestor of all living grasses.

For more on this fascinating and vital family of plants, pleas see this site by Peter Stevens from the Missouri Botanical Gardens.

Footnotes

  1. Estimated to be 6.7 billion people as of early 2010
  2. Currently (early 2010) most non-grass genomes come from a group of species called the rosids that are estimated to be around twice as old as the grasses