Figure 5.

Model of microsynteny between maize, sorghum, and rice in the 22-kDa α-zein cluster. In particular, maize and sorghum are highly related species. Most RFLP markers, genes and other known single- or low-copy sequences from both species cross-hybridize in highly stringent conditions and have a conserved genetic order, despite a 4-fold difference in genome size (6). However, most of the high-copy DNA does not cross-hybridize at the same conditions. Low- or single-copy sequences constitute a small fraction of the total genome in maize. They are immersed in large sections of high-copy DNA. The differential divergence between highly repetitive and low-copy DNA in maize and sorghum allows us to identify gene-like sequences in either direction among large segments of repetitive DNA in the cluster. Furthermore, the 22-kDa zein and kafirin multigene family is absent in rice. Therefore, the rice genome, in particular, should be useful to identify the nonzein, low-, or single-copy sequences in maize.