Apomixis: Genetics and Breeding

We have developed an approach for the in situ detection of genomic elements that regulate transcription zin Drosophila melanogaster. The approach is analogous to a powerful method of bacterial genetics, the random generation of operon fusions, that enables the isolation and characterization of genes simply by knowing or postulating their pattern of expression; it is not necessary initially to screen for mutant phenotypes. To apply this approach to Drosophila, we have used the expression of the lacZ gene of Escherichia coli from the P-element promoter in germ-line transformant flies to screen for chromosomal elements that can act at a distance to stimulate expression from this apparently weak promoter. Of 49 transformed fly lines obtained, approximately 70% show some type of spatially regulated expression of the lacZ gene in embryos; many of these express lacZ specifically in the nervous system. The P-lacZ fusion gene is, therefore, an efficient tool for the recovery of elements that may regulate gene expression in Drosophila and for the generation of a wide variety of cell-type-specific markers.

Genetic linkage maps have been constructed for the rice and maize genomes on the basis of orthologous loci detected with a common set of cDNA clones. Conserved linkage groups could be identified, which together account for more than two-thirds of both genomes. In some instances, entire chromosomes or chromosome arms are nearly identical with respect to gene order and gene content. The results also reveal that most of the genes (> 72%) duplicated during ancient polyploidization are still present in the maize genome in duplicate copy. The comparative maps of rice and maize provide a basis for interpreting molecular, genetic, and breeding information between these two important species and establish a framework for ultimately connecting the genetics of all grass species.