Plant bZIP G-box binding factors - Modular structure and activation mechanisms

In this review we sum-up the knowledge about bZIP G-box binding factors (GB Fs), which possess an N-terminal, proline-rich domain. The GBF has been one of the most extensively studied transcription factor family. Based on prot ein sequence homology with yeast and animal basic leucine-zipper (bZIP) tra nscription factors, bioinformatic studies have identified their main struct ural domains (proline-rich, basic and leucine-zipper). which have been furt her functionally characterized by in vitro and in vivo experiments. Recent reports have led to the discovery of other GBF-specific short amino-acid se quences that may take part in the regulation of gene expression by posttran scriptional modifications or interaction with other proteins such as bZIP e nhancing factors or plant 14-3-3-like proteins. We identified a GBF region, called the 'multifunctional mosaic region', that may be implicated in cyto plasmic retention, translocation to the nucleus and regulation of transcrip tion. We also identified many conserved protein motifs that suggest a modul ar structure for GBFs. At the whole plant level, GBFs have been shown to be involved in developmental and physiological processes in response to major cues such as light or hormones. Nevertheless, it remains difficult to assi gn a physiological role to a particular GBF protein modular structure. Fina lly, bringing together these different aspects of GBF studies we propose a model describing the puzzling transduction pathway involving GBFs from cyto plasmic events of signal transduction to the regulation of gene expression in the nucleus.