5′ Analysis of the soybean leghaemoglobin lbc 3 gene: regulatory elements required for promoter activity and organ specificity

Abstract

The soybean leghaemoglobin Ibc3 gene promoter was analys-ed in transgenic Lotus corniculatus plants. Hybrid-promoter constructions and 5' deletions were studied using chimneric genes composed of the various promoters, the chloram-phenicol acetyltransferase (CAT) coding sequence and the lbc3 3' flanking region. A 5' Bal31 deletion series mapped a strong positive regulatory element between -1100 and -950. A weaker element located between -230 and -170 defined the minimum 5' region required for detectable promoter ac-tivity. Reactivation of inactive promoters with deletion end-points between -230 and the transcription initiation site was obtained employing the constitutive cauliflower mosaic virus (CaMV) 35S enhancer. The position of cis regulatory ele-ment(s) required for nodule-specific expression was defined to 37 bp between -139 and -102. This region contains se-quences conserved in other leghaemoglobin and nodulin genes. No indispensable control elements were found on the Ibc3 3' flanking region. Key words: promoter elements/Bal31 deletions/hybrid promo-ters/root nodule expression/transgenic legumes leghaemoglobin Lba, Lbc1, Lbc2, Lbc3, polypeptides, which regulate the oxygen concentration within the nodule (Fuchsmann and Appleby, 1979). The corresponding lb genes have been characterized (Hyldig-Nielsen et al., 1982; Wiborg et al., 1982), and recently the Ibc3 gene was transferred into another legume Lotus corniculatus (Stougaard et al., 1986, 1987b). Both the gene itself and a chimeric CAT-gene under control of the Ibc3 5' and 3' flanking regions were nodule-specifically expressed, indicating a conserved regulatory mechanism for lb gene expression among E Introduction Few cases of organ development from differentiated somatic cells are known in higher eukaryotes. One such example is root nodule development from root cortex cells of legumes. After infection