Gijs J. H. van Rooijen

Regulation of an Arabidopsis oleosin gene promoter in transgenic Brassica napus

Progressive deletions of the 5′-flanking sequences of an Arabidopsis oleosin gene were fused to β-glucuronidase (GUS) and introduced into Brassica napus plants using Agrobacterium-mediated transformation. The effect of these deletions on the quantitative level of gene expression, organ specificity and developmental regulation was assessed. In addition, the influence of abscisic acid (ABA), jasmonic acid (JA), sorbitol and a combined ABA/sorbitol treatment on gene expression was investigated. Sequences that positively regulate quantitative levels of gene expression are present between −1100 to −600 and −400 to −200 of the promoter. In addition, sequences present between −600 and −400 down-regulate quantitative levels of expression. In transgenic B. napus plants, the oleosin promoter directs seed-specific expression of GUS which is present at early stages of seed development and increases throughout seed maturation. Sequences present between −2500 and −1100 of the promoter are involved in modulating the levels of expression at early stages of embryo development. Histochemical staining of embryos demonstrated that expression is uniform throughout the tissues of the embryo. Sequences involved in the response to ABA and sorbitol are present between −400 and −200. The induction of GUS activity by a combined ABA/sorbitol treatment is additive suggesting that ABA is not the sole mediator of osmotically induced oleosin gene expression. A response to JA was only observed when the oleosin promoter was truncated to −600 suggesting that the reported effect of JA on oleosin gene expression may be at a post-transcriptional level.

Phytohormones and osmotic stress in the regulation of embryo-specific gene expression in Brassica napus microspore embryos

ABA has been shown to be involved in the control of many events during embryogenesis and seed development (Shiver and Mundy, 1990). Many of the responses stimulated by ABA are also affected by water stress or elevated osmotica (Finkelstein et al. 1985; Finkelstein and Crouch, 1986; Finkelstein and Somerville, 1989). The relationship however between ABA and these osmotic effects is still not clear. Some evidence suggests that ABA and osmoticum act through independent mechanisms (Finkelstein and Crouch, 1986), other reports suggest a mediating role for ABA in osmotic stress(e.g. Bray and Beachy, 1985).