Ancient polyploidization predating divergence of the cereals

The extent of genetic and genomic information available on several species, such as barley, wheat, maize, rice, and sorghum, which belong to different tribes in the grass family, has enabled some of the most comprehensive comparative genomics studies in plants.

From an evolutionary standpoint, the grass family is fascinating because of the degree of variation found in overall size, ploidy level, and chromosome number.

For example, bread wheat (; 2n = 24) has a much smaller genome of 0.4 Gb (sizes refer to the haploid genome in each case).

Unraveling the course of grass genome evolution from a common ancestor is a daunting task, but it is one that might also reveal common properties of eukaryotic genome evolution in general. (pages 11–24) provide a comprehensive analysis of intragenomic duplications and comparative synteny in rice and wheat.


This allowed the identification of duplications covering ∼70% of both the rice and wheat genomes.The authors then conducted a detailed analysis of the length, composition, and divergence time of these duplications and made comparisons with sorghum and maize.The grass family, which includes more than 10,000 species, is the single most important family in agriculture.Although relatively small compared with other flowering plant families, it surpasses all others in economic importance (maize, wheat, and rice alone account for a major portion of food calories consumed worldwide) and in ecological importance as well (grasses cover 20% of the earth's land surface and often dominate temperate and tropical habitats) (Gaut, 2002).

This led to a model of grass genome evolution from a common ancestor with a basic number of five chromosomes.

The authors suggest that the common ancestor with = 12 intermediate ancestor that has been described previously (see figure ). (2007), rice has retained this intermediate ancestral chromosome number, whereas it has been reduced in the wheat, maize, and sorghum genomes, following a pattern that may be typical of plant chromosome evolution in general. The five ancestral chromosomes are named according to rice nomenclature. continues to propose how the genomes of rice, wheat, maize, and sorghum evolved from the The analytical methods employed by Salse et al.


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