ANALYSIS OF ZEIN GENE EXPRESSION IN MAIZE

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The zein genes of maize encode the seed storage proteins. Zeins constitute 60% of the endosperm protein and consist of four structurally distinct types: the sulfur-poor alpha -zeins, and the sulfur-rich beta, gamma, and delta -zeins. The alpha -zeins are encoded by a large multigene family of possibly 75 to 100 genes, while the beta, gamma, and delta -zeins are each encoded by only one or two genes. A number of mutations have been identified that cause a reduction in the synthesis of alpha -zeins. At least one of these, opaque-2, corresponds to a transcriptional regulatory protein that affects the expression of certain members of the alpha -zein gene family. However, the mechanisms by which most of these mutations affect the expression of specific zeins are not understood. Little is known about the regulation of the genes encoding the sulfur-rich zeins. Recently we characterized a group of genes called opaque-2 'modifiers.' The "modified' opaque lines of maize contain two to four times as much gamma zein as standard opaque-2 mutants. The "modifiers' appear to be dominant genes that specifically increase the expression of the gamma -zein genes. We propose to: (1) Determine how the opaque-2 'modifiers" affect the expression of gamma -zein genes (2) Investigate the genetic complexity of opaque-2 "modifiers' and begin to identify and isolate modifier genes (3) Test the hypothesis that it is the high content of gamma -zein and its distribution that are responsible for the vitreous phenotype of modified opaque kernels, and (4) Further characterize the DNA sequences that direct the transcription of alpha ,beta, and gamma -zein genes and identify the proteins regulating their transcription. In addition to expanding our understanding of tissue-specific gene expression, the results of these studies will have application to the improvement of maize protein and seed quality.