INDUCTION AND EXPRESSION OF SEED-SPECIFIC PROMOTERS IN ARABIDOPSIS EMBRYO-DEFECTIVE MUTANTS

In order to assess the importance of morphogenesis on the induction of promoter markers for storage and Lea programmes, advantage was taken of the emb mutations producing embryos arrested at a wide range of dev elopmental stages in Arabidopsis. These embryos are viable during thei r stage of developmental arrest and continue to divide further, but ap parently without further differentiation into the main organs and tiss ues of the normal embryos. Eight independent emb mutants arrested in t heir development prior to the cotyledon stage were selected. These emb embryos lack the normal morphology of the wild-type embryos when the synthesis of storage and Lea proteins are normally initiated. The 2S1- uidA chimeric gene, representative of the maturation programme and the Em 1-uidA chimeric gene, representative of the desiccation programme were introduced by crosses into the emb background. In the eight emb l ines, the expression of the GUS reporter gene directed by the 2S1 and Em 1 promoters was observed in the aborted seeds irrespective of their stage of developmental arrest. The time of induction of the expressio n of both promoters was the same in the arrested embryos as compared w ith the normal embryos within the same silique. Thus, the activation o f these two promoters is triggered by the same signal and can occur in the absence of morphogenesis. However, in the absence of normal organ formation, the expression of the reporter gene under the control of t he 2S1 and Em 1 promoters was evident throughout the whole seed tissue s. In normal seed development, the hormone abscisic acid (ABA) activat es the promoters of the 251 and Em 1 genes. One of the important membe rs of the signal transduction pathway of ABA is the ABl3 protein. It h as been shown previously that this protein is a prerequisite for the i nduction of Em 1 by ABA in seeds. A good correlation with the expressi on of the AB13 promoter and the 2S1 and Em 1 promoters was found in em b seeds tissues. This observation suggests that the promoters of the 2 51 and the Em 1 genes are expressed in the mutant seeds not at a basal level, but are probably induced by ABA, as in normal seed development .