The complete sequence of 340 kb of DNA around the rice Adh1-Adh2 region reveals interrupted colinearity with maize chromosome 4

A 2.3-centimorgan (cM) segment of rice chromosome 11 consisting of 340 kb o f DNA sequence around the alcohol dehydrogenase Adh1 and Adh2 loci was comp letely sequenced, revealing the presence of 33 putative genes, including se veral apparently involved in disease resistance. Fourteen of the genes were confirmed by identifying the corresponding transcripts. Five genes, spanni ng 1.9 cM of the region, cross-hybridized with maize genomic DNA and were g enetically mapped in maize, revealing a stretch of colinearity with maize c hromosome 4. The Adh1 gene marked one significant interruption. This gene m apped to maize chromosome 1, indicating a possible translocation of Adh1 af ter the evolutionary divergence leading to maize and sorghum. Several other genes, most notably genes similar to known disease resistance genes, showe d no cross-hybridization with maize genomic DNA, suggesting sequence diverg ence or absence of these sequences in maize, which is in contrast to severa l other well-conserved genes, including Adh1 and Adh2 These findings indica te that the use of rice as the model system for other cereals may sometimes be complicated by the presence of rapidly evolving gene families and micro translocations. Seven retrotransposons and eight transposons were identifie d in this rice segment, including a Tc1/Mariner-like element, which is new to rice. In contrast to maize, retroelements are less frequent in rice. Onl y 14.4% of this genome segment consist of retroelements. Miniature inverted repeat transposable elements were found to be the most frequently occurrin g class of repetitive elements, accounting for 18.8% of the total repetitiv e DNA.