The Sorghum bicolor genome and the diversification of grasses
Sorghum, an African grass related to sugar cane and maize, is grown for food, feed, fibre and fuel. We present an initial analysis of the similar to 730- megabase Sorghumbicolor ( L.) Moench genome, placing, 98% of genes in their chromosomal context using whole- genome shotgun sequence validated by genetic, physical and syntenic information. Genetic recombination is largely confined to about one- third of the sorghum genome with gene order and density similar to those of rice. Retrotransposon accumulation in recombinationally recalcitrant heterochromatin explains the similar to 75% larger genome size of sorghum compared with rice. Although gene and repetitive DNA distributions have been preserved since palaeopolyploidization similar to 70 million years ago, most duplicated gene sets lost one member before the sorghum - rice divergence. Concerted evolution makes one duplicated chromosomal segment appear to be only a few million years old. About 24% of genes are grass- specific and 7% are sorghum- specific. Recent gene and microRNA duplications may contribute to sorghum’s drought tolerance.