The cereal endosperm is a major organ of the seed and an important component of the world’s food supply. Tounderstand the development and physiology of the endosperm of cereal seeds, we focused on the identification ofgenes expressed at various times during maize endosperm development. We constructed several cDNA libraries toidentify full-length clones and subjected them to a twofold enrichment. A total of 23,348 high-qualitysequence-reads from 5-and 3-ends of cDNAs were generated and assembled into a unigene set representing 5326genes with paired sequence-reads. Additional sequencing yielded a total of 3160 (59%) completely sequenced,full-length cDNAs. From 5326 unigenes, 4139 (78%) can be aligned with 5367 predicted rice genes and by takingonly the "best hit" be mapped to 3108 positions on the rice genome. The 22% unigenes not present in rice indicatea rapid change of gene content between rice and maize in only 50 million years. Differences in rice and maize genenumbers also suggest that maize has lost a large number of duplicated genes following tetraploidization. The largernumber of gene copies in rice suggests that as many as 30% of its genes arose from gene amplification, which wouldextrapolate to a significant proportion of the estimated 44,027 candidate genes of its entire genome. Functionalclassification of the maize endosperm unigene set indicated that more than a fourth of the novel functionallyassignable genes found in this study are involved in carbohydrate metabolism, consistent with its role as a storageorgan.

Data from cytological and genetic mapping studies suggest that maize arose asa tetraploid. Two previous studies investigating the most likely mode of maizeorigin arrived at different conclusions. Gaut and Doebley [7] proposed a segmentalallotetraploid origin of the maize genome and estimated that the two maizeprogenitors diverged at 20.5 million years ago (mya). In a similar study, using largerdata set, Brendel and colleagues (quoted in [8]) suggested a single genome duplicationat 16 mya. One of the key components of such analyses is to examine sequencedivergence among strictly orthologous genes. In order to identify such genes, Laiand colleagues [10] sequenced five duplicated chromosomal regions from the maizegenome and the orthologous counterparts from the sorghum genome. They alsoidentified the orthologous regions in rice. Using positional information of geneticcomponents, they identified 11 orthologous genes across the two duplicated regionsof maize, and the sorghum and rice regions. Swigonova et al. [12] analyzed the 11orthologues, and showed that all five maize chromosomal regions duplicated at thesame time, supporting a tetraploid origin of maize, and that the two maize progenitorsdiverged from each other at about the same time as each of them diverged fromsorghum, about 11.9 mya. Copyright  2004 John Wiley & Sons, Ltd.

The amino acid methionine is a common protein building block that is also important in other cellularprocesses. Plants, unlike animals, synthesize methionine de novo and are thus a dietary source of thisnutrient. A new approach for using maize as a source of nutrient methionine is described. Maize seeds, amajor component of animal feeds, have variable levels of protein-bound methionine. This variability is aresult of post-transcriptional regulation of the Dzs10 gene, which encodes a seed-speci®c highmethioninestorage protein. Here we eliminate methionine variability by identifying and replacing thecis-acting site for Dzs10 regulation using transgenic seeds. Interestingly, two different mechanisms affectmRNA accumulation, one dependent on and the other independent of the untranslated regions (UTRs) ofDzs10 RNA. Accumulation of chimeric Dzs10 mRNA was not reduced in hybrid crosses and wasuncoupled from genomic imprinting by Dzr1, a regulator of Dzs10. Uniform high levels of Dzs10 proteinwere maintained over ®ve backcross generations of the transgene. The increased level of methionine inthese transgenic seeds allowed the formulation of a useful animal feed ration without the addition ofsynthetic methionine.