BAI1: A Plant Transcription Factor Governing Nuclear and Plastid Gene Expression

Plant cell organelles, such as mitochondria and plastids, possess their own genomes and gene expression machinery, yet most of their proteins are encoded by the nuclear genome. Consequently, tight coordination between nuclear and organellar gene expression is essential to ensure proper organelle biogenesis and maintenance in response to developmental and environmental cues. By recognizing specific cis-regulatory sequences, transcription factors (TFs) play central roles in orchestrating these processes and the associated signaling networks. As sessile organisms, plants have evolved an extensive array of TFs to cope with a broad spectrum of internal and external challenges. Notably, Arabidopsis thaliana encodes over 1500 TFs, nearly half of which are specific to plants, reflecting the unique regulatory strategies developed within this kingdom (Riechmann et al., 2000). A critical aspect of TF function lies in their ability to recognize and interact with target DNA sequences. The kinetics of DNA binding and the turnover of TFs depend not only on their intrinsic DNA-binding specificity but also on interactions with other regulatory proteins expressed in a highly specific spatial and temporal manner. These partners include other TFs, co-factors, and chromatin modifiers. Many TFs are constitutively expressed but remain inactive until triggered by specific signals. Common regulatory strategies include sequestration in the cytoplasm or tethering to cellular membranes, awaiting the appropriate stimulus. Moreover, many TFs carry multiple targeting signals, allowing for a dynamic and finely tuned regulation of gene expression that is dependent on subcellular localization.