Abstract
Glutamine synthetase 1–2 (GS 1–2), one of the six glutamine synthetase (GS) genes found in the maize ( Zea mays L.) genome, encodes a cytoplasm-localized GS isozyme (GS p1) that is specifically expressed in the basal maternal tissues of the developing kernel. This gene has now been isolated, and its 5′ upstream regulatory region has been sequenced and then used to drive reporter gene expression in stable maize transformants. Expression of the GS 1–2 promoter/GUS heterologous gene resulted in the predicted tissue-specific expression in the basal maternal seed tissues, including the surrounding pericarp. Gene expression within the pedicel parenchyma that subtends the basal endosperm transfer cells and embryo was particularly strong. In contrast, GUS staining was absent in the endosperm and embryo, as well as in leaves or roots. Strong staining was also observed in the basal tissues of developing anthers, which are anatomically similar to the pedicel, and in mature pollen. Silks and husks also stained weakly. A possible explanation for ecotopic expression of GS 1–2/GUS in pollen is presented. The GS 1–2 expression pattern within the kernel is consistent with the GS p1 isozyme's recognized role in nitrogen metabolism during grain fill.
Published Version
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