Expression of an ABA-induced gene of tomato in transgenic tobacco during periods of water deficit

Abstract

The gene le25 is an abscisic acid (ABA)-induced gene of tomato which is expressed both in wilted vegetative organs and developing seeds. Spatial and temporal expression was analysed in tobacco plants transformed with a chimeric gene in which 5'-upstream DNA sequences of le25 were fused to the E. coli uidA gene, which encodes β-glucuronidase (GUS). Histochemical staining revealed that GUS was expressed in all tissues of vegetative organs in response to water deficit. Exogenous ABA induced expression to a lesser extent, even though ABA content was the same as drought-stressed leaves, indicating a difference in response to endogenous ABA compared to exogenous ABA. Water-deficit-induced GUS expression in floral tissues was examined in pre-anthesis floral buds from four different stages (I-IV ; 11, 16, 33, 49 mm bud length, respectively). While non-stressed floral organs showed no GUS activity except in pollen at stages III and IV, GUS activity was water-deficit-induced in sepals of all stages, petals of stage II, and stigmas of stage II and III. In seeds, GUS activity was detected in both the embryo and endosperm at 15 d post-anthesis, which coincided with a large increase in the concentration of ABA in the seed. In transgenic plants, the le25 5'-flanking DNA drove expression of GUS during water deficit in two modes : non-tissue-specific expression in vegetative organs, and tissue-specific expression in reproductive organs. The location of GUS activity indicated that ABA concentration is elevated throughout the tissues of the leaf during periods of water deficit.