GA-induced gene expression in petunia flowers

The plant hormone gibberellin (GA) plays an essential role in a wide range of developmental processes including petal growth and pigmentation (Huttly, Phillips 1995). We have previously shown that GA is essential for Petunia hybrida flower development (Weiss, Halevy 1989). When detached petunia corollas were grown in vitro in a sucrose medium, they elongated and became pigmented only in the presence of GA3 (Weiss et al. 1992). Analysis of endogenous GAs indicated the presence of biologically active GAs, including GA1 and GA4, in the anthers and corollas at the stages of rapid elongation and anthocyanin accumulation (Weiss et al. 1995). The effect of the hormone on corolla pigmentation was due to the activation of the anthocyanin biosynthetic genes such as chalcone synthase (chs) (Weiss et al. 1992). However, the effect of the hormone is not exclusive to these genes; it also promotes the expression of genes from general metabolic pathways, such as triosephosphate isomerase (tpi) (Ben-Nissan, Weiss 1995). Recently, we have cloned (Ben-Nissan, Weiss 1996) the petunia homologue (gip) of the tomato gast1 (Shi et al. 1992). Gip is expressed in corollas during cell elongation and is induced specifically by GA3. Expression analysis of the gene provided evidence supporting its possible role in GA-induced corolla elongation (Ben-Nissan, Weiss 1996).