Submitted to: Proceedings of Int'l Association of Plant Tissue Culture and Biotechnology
Publication Type: Abstract Only
Publication Acceptance Date: 6/28/2002
Publication Date: N/A
Technical Abstract: Glutamine synthetase (GS), plays several central roles in plant nitrogen metabolism including initial incorporation of inorganic nitrogen, nitrogen recapture in photo-respiration and nitrogen mobilization in senescence and seed fill. In maize, GS is encoded as a single plastid gene and five cytoplasmic genes. The protein (GSp1) derived from the cytoplasmic gene GS1-2 is found in abundance within the pedicel and surrounding pericarp of developing seeds and is believed to be an important regulatory enzyme in nitrogen assimilation into developing maize kernels. This gene has now been isolated, its 5' upstream regulatory region has been sequenced and a 664 bp upstream region used to express beta-glucuronidase (GUS) in stably transformed maize plants. GUS expression was very strong in the basal maternal seed tissues, including the surrounding pericarp and was also evident in the bases of developing anthers, but did not accumulate in leaves, roots, endosperm or embryo tissues. GUS expression was also noted in pollen in some lines, despite GSp1 not being found in pollen. Deletion series analysis of the promoter indicates that a sequence between -664 and -400 confers maternal tissue specificity. The second intron also appears essential as its removal also abolishes tissue specificity as well. The GS1-2 promoter's strong expression in maternal seed tissues is consistent with the GS isozyme's role in nitrogen metabolism during grain fill. The promoter could be used to modify carbon and nitrogen assimilation into developing kernels or to add disease resistance factors into critical pericarp and pedicel tissues.