The ABSCISIC ACID-INSENSITIVE 3 (ABI3) gene is expressed during vegetative quiescence processes in Arabidopsis

The ABSCISIC ACID-INSENSITIVE 3 (ABI3) gene of Arabidopsis thaliana (L.) Heynh is known to play an important role during seed maturation and dormancy. Here, we present evidence suggesting an additional role for ABI3 during vegetative quiescence processes. During growth in the dark, ABI3 is expressed in the apex of the seedlings after cell division is arrested. The 2S seed storage protein gene, a target gene of ABI3 in seeds, is also induced in the arrested apex under similar darkness conditions. In addition, beta-glucuronidase expression under the control of the ABI3 promoter is abolished by treatments that provoke leaf development in the dark [sucrose and abscisic acid (ABA) biosynthesis inhibitors] and induced by treatments that prevent leaf development (darkness and ABA), Furthermore, ABI3 expression is absent in apices of dark-grown de-etiolated (det 1) and abi3 mutants, both known to develop leaves or leaf primordia in the dark. The fact that the expression of the ABI3 gene is only observed in a fraction of the analysed plants suggests that ABI3 is probably only one of the components of a molecular network underlying quiescence. In addition to the expression of ABI3 in apices of dark-grown seedlings, the ABI3 promoter confers expression in other vegetative organs as well, such as the stipules and the abscission,zones of the siliques, In conclusion, apart from its role in seed development, ABI3 might have additional functions.