Effect of the cauliflower mosaic virus 35S, actin, and ubiquitin promoters on UidA expression from a bar-uidA fusion gene in transgenic Gladiolus plants

Abstract

Tissue-specific patterns and levels of gene expression were characterized in transgenic Gladiolus plants that contained the phosphinothricin acetyltransferase (bar)-β-glucuronidase (uidA) fusion gene under transcriptional control of the promoter from either the cauliflower mosaic virus 35S (CaMV 35S), duplicated CaMV 35S (2×CaMV 35S), rice actin (Act1), or Arabidopsis ubiquitin (UBQ3) promoters. The bar gene confers resistance to phosphinothricin (PPT)-containing herbicides and allowed selection of transgenic cells. The β-glucoronidase gene encoded by the uidA locus of E. coli functioned as a reporter gene. Maximum levels of β-glucuronidase (GUS) activity in leaves were 173, 112, 50, and 10 nmoles 4-methylumbelliferone h−1 mg−1 protein for transgenic plants with the bar-uidA fusion gene under the control of the CaMV 35S, 2×CaMV 35S, UBQ3, and Act1 promoters, respectively. There was frequently considerable variability in GUS activity between the leaves of a single plant, and levels of uidA expression varied between independently transformed plants for each promoter. Callus derived from transgenic plants showed much less variation in GUS expression than leaves. The mean level of GUS activity was significantly higher (over 3×) for transgenic lines of callus containing the CaMV 35S as compared to the UBQ3 promoter, and this confirmed the higher (2×) level of GUS activity in levels of plants with the CaMV 35S promoter as compared to the UBQ3 promoter. Tissue-specific patterns of uidA expression were determined by histochemical staining. Leaves 5–6 cm long from plants with any of the four promoters tested exhibited uidA expression primarily in the vasculature. Under all four promoters uidA was expressed more frequently in root tips as compared to leaves.