PLANT PHYSIOLOGY , Vol 106, Issue 3 929-939, Copyright © 1994 by American Society of Plant Biologists

MOLECULAR BIOLOGY AND GENE REGULATION

The Regulation of Gene Expression in Transformed Maize Aleurone and Endosperm Protoplasts (Analysis of Promoter Activity, Intron Enhancement, and mRNA Untranslated Regions on Expression)

D. R. Gallie and T. E. Young
Department of Biochemistry (D.R.G.) and Department of Botany and Plant Sciences (T.E.Y), University of California, Riverside, California 92521-0129

Gene expression in the aleurone and endosperm is highly regulated during both seed development and germination. Studies of [alpha]-amylase expression in the aleurone of barley (Hordeum vulgare) have generated the current paradigm for hormonal control of gene expression in germinating cereal grain. Gene expression studies in both the aleurone and endosperm tissues of maize (Zea mays) seed have been hampered because of a lack of an efficient transformation system. We report here the rapid isolation of protoplasts from maize aleurone and endosperm tissue, their transformation using polyethylene glycol or electroporation, and the regulation of gene expression in these cells. Adh1 promoter activity was reduced relative to the 35S promoter in aleurone and endosperm protoplasts compared to Black Mexican Sweet suspension cells in which it was nearly as strong as the 35S promoter. Intron-mediated stimulation of expression was substantially higher in transformed aleurone or endosperm protoplasts than in cell-suspension culture protoplasts, and the data suggest that the effect of an intron may be affected by cell type. To examine cytoplasmic regulation, the 5[prime] and 3[prime] untranslated regions from a barley [alpha]-amylase gene were fused to the firefly luciferase-coding region, and their effect on translation and mRNA stability was examined following the delivery of in vitro synthesized mRNA to aleurone and endosperm protoplasts. The [alpha]-amylase untranslated regions regulated translational efficiency in a tissue-specific manner, increasing translation in aleurone or endosperm protoplasts but not in maize or carrot cell-suspension protoplasts, in animal cells, or in in vitro translation lysates.

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