Plant & Animal Genomes XIII Conference Plant & Animal Genomes XIII ConferenceJanuary 15-19, 2005
Town & Country Convention Center
San Diego, CA
Common wheat has a 17,300 Mb genome of which the vast majority (greater than 90%) is composed of non-genic repetitive DNA. Wheat genes appear to be clustered in small physical segments (gene islands) characterized by high recombination rates. The gene islands, in turn, are separated from each other by large, gene-poor stretches composed mostly of retrotransposon-like repeats. Recently, gene-enrichment strategies have been developed to help those studying large repetitive genomes skim gene-rich regions out of the veritable ‘sea or repetitive DNA’ in which they reside. The two most prevalent gene-enrichment strategies are methylation filtration (MF) and Cot-filtration (CF). MF is rooted in the observation that plant genes tend to be hypomethylated compared to repeat sequences. In MF, sheared genomic DNA is ligated into a vector and used to transform a bacterial strain that contains a methylation-sensitive restriction system. The restriction system cleaves most hypermethylated insert sequences, and consequently only clones containing hypomethylated DNA (ostensibly genes) are successfully propagated. CF, on the other hand, is based on the principles of DNA reassociation kinetics. In short, hydroxyapatite chromatography is used to separate those sequences that renature quickly (i.e., repeat or low Cot sequences) from those that renature slowly (low-copy or high Cot sequences). The low-copy sequences are then cloned. MF and CF gene-enrichment strategies have proven useful in the maize genome sequencing effort, and initial results in wheat suggest that these techniques should greatly accelerate characterization of the wheat gene space.