Genome science of polyploid wheat

摘要

Polyploidy is a characteristic feature of plant genomes (Soltis and Soltis 2000; Vision et al. 2000; Wendel 2000), and as much as 70% of all angiosperms were polyploid at some stage during their evolution (Masterson 1994; Leitch and Bennett 1997). Polyploidy leads to an increase in gross genetic information, but its presence makes it difficult to analyze genome structure and gene regulation. Common wheat, which is characterized by polyploidy, is an allohexaploid that possesses three distinct genomes(AABBDD; Lilienfeld 1951). Because the genetic relationships among wheat species have been extensively characterized (Tsunewaki 1993), wheat species (Triticum-Aegilops group) can be used as a model system to study the genomics of polyploid plants. However, the wheat genome is exceptionally large, with a diploid genome of about 5 gigabase pairs (Gbp). Thus, allohexaploid common wheat possesses a genome of approximately 16 Gbp, which is 40 times the size of the rice genome (430 MB; Sasaki 2003). This inherent complexity has led geneticists to carry out their studies of the wheat genome using expressed sequence tags (ESTs). In fact, as of June 10, 2005, there are approximately 590,000 wheat ESTs available in the National Center for Biotechnology Information EST database (http://www.ncbi.nhn.nih.gov/dbEST/ dbEST_summary.html).