Rice Genetics IV - IRRI books - International Rice Research Institute

Arabidopsis, long heralded as a “simple” model diploid, turns out to be more than60% duplicated (The Arabidopsis Genome Initiative 2000). Rice is almost certainlyno exception.Information concerning ancient large duplications in the grasses is beginning toemerge from analyses at the map level. The R11/R12 duplication, which involvessubstantial portions of the short arms of both rice chromosomes, was originally thoughtto be specific to rice (Nagamura et al 1995). However, the same duplication has nowbeen shown to exist in pearl and foxtail millet (Fig. 3). Thus, this duplication clearlypredates the divergence of the Bambusoideae and Panicoideae subfamilies. As moreduplications are identified, these will be useful predictors for the taxonomists; however,they will also disrupt other applications that rely on close colinearity.Underresearched cereals—the “orphan” cropsThe discovery of general syntenic relationships among groups of plants will be ofimmense benefit to “orphan” crops. In fact, all initial mapping projects forunderresearched minor crops should include a comparative approach at the earlieststage, because, once maps have been aligned, the presence, location, and modes ofaction of key genes can be predicted from knowledge gained in other cereals. Anexample is foxtail millet, Setaria italica, a crop of agricultural significance only innorthern China. Although foxtail millet has received very little research attention inthe past, it has recently achieved a considerable genetic base by the simple strategy ofhaving its 2n=2x=18 genome aligned with rice (Devos et al 1998). QTL analyses ofan interspecific foxtail millet and S. viridis segregating population have revealed thePoaceaeOryzoideae Panicoideae Pooideae11 12S SVIIITVIIT1 4B BXpsm196Xrgc920Xrgc104Xrgr642Xrgr1534Rice Foxtail millet Pearl milletFig. 3.The R11/R12 duplication in rice, foxtail millet, and pearl millet. Note: Thefigure shows that RFLP markers that define rice duplication are similarly duplicatedand map in the same linear orders in the other two species. T and B representthe top and bottom of the chromosome arms. S is the short arm.84 Gale et al