Rice Genetics IV - IRRI books - International Rice Research Institute

The solid base laid by classical rice geneticists and breeders around the world overthe past century has allowed successful launches of several major research initiatives.One, the Rockefeller Foundation’s International Program on Rice Biotechnology(Toenniessen 1998), was particularly farsighted and started in 1984. This was followedby national programs such as the Korean effort centered in Suwon and theJapanese Rice Genome Program based at Tsukuba. Rice is an important staple foodcrop and it has a much smaller genome than many other cereals—11 times smallerthan that of maize and 40 times smaller than that of wheat. As a result, rice has rapidlybecome the most-researched cereal. Denser molecular maps and more DNA resources,including random fragment length polymorphism (RFLP) probes, microsatellite markers,expressed sequence tags (ESTs), bacterial and yeast artificial chromosome (BACand YAC) libraries, and the genomic sequence, are available in rice than in any othercereal. Because considerable sequencing of rice has already taken place in Monsantoand Syngenta and the public international rice genomic sequencing effort is well underway will only increase the pace and central importance of rice genetics research.Cereal comparative geneticsIncreasingly, rice is being studied in laboratories that previously concentrated on onlywheat or maize. The single major factor that has led to the promotion and use of riceas a model has been the discovery of an unexpectedly high degree of similarity betweendifferent cereal genomes in terms of gene content and gene order. It is nowbeing recognized that conserved colinearity is the rule rather than the exception andthat it exists to a greater or lesser extent in all groups of plants, animals, and microbes.However, the critical observations were first made in the cereals in the late 1980s.Early reports included the comparisons of the three genomes of hexaploid bread wheat(Chao et al 1989), comparisons of the genomes of wheat and rye (Devos et al 1993),and comparative maps of rice and maize (Ahn and Tanksley 1993) and rice and wheat(Kurata et al 1994, Van Deynze et al 1995b). We now understand that the relationshipsbetween various cereal genomes are so close that all of the genomes investigatedto date can be shown as a single synthesis, irrespective of chromosome numberor total DNA content (Fig. 1).Other grasses of lesser global economic significance have later been shown todisplay similar close synteny with rice. These comparative studies include sorghum(Dufour et al 1997), sugarcane (Glaszmann et al 1997), foxtail millet (Devos et al1998), oats (Van Deynze et al 1995a), pearl millet (Devos et al 2000), and Zizania(Kennard et al 1999). Others that will follow over the next year or so include theforage grasses, fescue (O.-A. Rognli, personal communication) and ryegrass (J. Foster,personal communication), finger millet (M.M. Dida and K.M. Devos, personalcommunication), and tef (M. Sorrells, personal communication). There will be differencesof evolutionary origin in the detail, but overall it is clear that, in the end, allgrass genomes will be described by only a few rice linkage blocks (Gale and Devos1998).80 Gale et al