REGULATION OF ABSCISIC ACID-INDUCED TRANSCRIPTION

The phytohormone abscisic acid is probably present in all higher plant s. This hormone is necessary for regulation of several events during s eed development and for the response to environmental stresses such as desiccation, salt and cold. An important part of the physiological re sponse to abscisic acid is achieved through gene expression. Here, we summarize the current knowledge of regulation of abscisic acid-induced transcription. The main focus is on a description of the known abscis ic acid-responsive cis-elements, their properties and the possible tra nsacting factors binding to the elements. Results have shown that coop erative action of cis-elements and the promoter configuraton is crucia l for regulation by abscisic acid. Furthermore, several elements are o rgan-and species-specific. Recent studies of the chromatin structure o f abscisic acid-responsive genes point to the importance of induction of transcription by coactivators or by phosphorylation/dephosphorylati on of transcription factors. An interesting example of activation by a cofactor is the cooperative action between abscisic acid-signaling an d the regulatory protein Viviparous 1 through the abscisic acid respon sive element.