Gama -coixina : isolamento do clone genomico e caracterização da região promotora

AUTOR(ES)
DATA DE PUBLICAÇÃO

1996

RESUMO

Prolamins, the major cereal storage proteins, are encoded by genes coordinately regulated in a tissue- and developmental stage-specific manner during seed development. There are several prolamin genes encoding proteins of discrete molecular sizes, which are divided in classes according to similarities in their primary structures and solubility. The expression of these genes is regulated primarily at the transcriptional level. The Coix prolamins, known as coixins, represent more than 70% of the total endosperm protein. Coixins can be separated in two fractions based on their differential solubility: (X- and y-coixins. The overall molecular data shows a high degree of similarity among the genes encoding the prolamins of maize, Coix and Sorghum. The coordinated expression of the prolamin genes is accomplished by a common regulatory mechanism. Still, recent studies on the opaque-2 mutation clearly demonstrated a distinct transcriptional regulation at the class level for the a- and p-prolamins. Therefore, multiple complex regulatory mechanisms are conceivably involved in the regulation of prolamin genes. Although the mechanisms of gene regulation for the a-prolamins are well studied, mostly because of the opaque-2 mutant of maize, little is known about the mechanisms controlling the y-prolamin genes. Also, while the a-prolamins are encoded by multigene families, the y-prolamíns are encoded by one or two genes, which heightens the importance of the y-prolamíns in molecular improving of cereais. In this work the y-coixin gene (I"GCX23.1) was isolated from a Coix genomic À-dash library. The library was screened using a y-coixin cDNA clone as probe. In order to elucidate the transcriptional regulation of the y-prolamin genes, the y-coixin promoter sequence was aligned with the promoter. sequences of the maize and sorghum y-prolamins genes. Several conserved motifs were found in the upstream region of these genes. Some of these motifs resembles cis-acting elements. such as the cereal prolamin box and the binding sites for yeast GCN4 and animal C/EBP transcriptional factors. Transient expression assays demonstrated the ability of the y-coixin promoter to drive the expression of the ?-glucuronidase reporter gene in immature maize endosperm. Deletion analysis of the promoter sequence suggested that several elements might be involved in its regulation. At least three distinct segments of the y-coixin promoter bind specifically to nuclear factors, as demonstrated by means of gel retardation assay

ASSUNTO(S)

coix cereais plantas - genetica molecular graminea - semente plantas - proteinas regulamento genetico clonagem molecular

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