ABI3 expression ceases following, but not during, germination of tomato and Arabidopsis seeds

In many plant species, including tomato and Arabidopsis, the inception of dormancy during seed development is mediated by abscisic acid (ABA) and the transcription factor ABSCISIC ACID INSENSITIVE3/VIVIPAROUS1 (ABI3/VP1). Consequently, seeds carrying mutations in this gene germinate precociously. The ABI3 orthologue isolated from tomato (LeABI3) is a single copy gene expressed only in seeds. ABI3 expression ceases following the completion of germination in both tomato and Arabidopsis seeds, suggesting that expression of this gene does not regulate germination. LeABI3 expression in tomato wild-type embryos, while present in intact seeds, is greater than in their isolated embryo axes. Decreased LeABI3 expression does not occur in isolated axes from the gibberellin (GA)-deficient gib-1 mutant of tomato, in contrast to embryos from the intact seeds. This is indicative of a signal passing from the endosperm to the embryo which acts to promote LeABI3 expression in the latter, and that this signal is GA or GA-derived.