CHAPTER 6 Plant transcription factors in light- regulated development and UV-B protection Deeksha Singh, Nevedha Ravindran, Nikhil Job, Puthan Valappil Rahul, Lavanya Bhagavatula and Sourav Datta Plant Cell and Developmental Biology Laboratory, Department of Biological Sciences, IISER Bhopal, Bhauri, Madhya Pradesh, India 6.1 Introduction The transcriptional regulation in plants governs several morphological and physiological changes in response to endogenous signals as well as environmental cues. Transcription factors (TFs) bind to cis-elements in the promoter region and regulate the target gene expression, either by acting as an activator or a repressor (Franco-Zorrilla et al., 2014; Badis et al., 2009). Additionally, TFs can bind to other TFs, microproteins, or ncRNA to regulate gene expression during various developmental stages (Song et al., 2021a). These interactions can either enhance their ability to bind to the target promoter leading to transcriptional activation or inhibit the binding onto the promoter, leading to the deactivation of the gene expression (Ye et al., 2004). Many TFs have been identified using methodologies that involve genetic screening and homology-based detection. Based on the protein structure and affinity to bind identical DNA sequences, TFs are categorized into different families, where TFs belonging to the same family are often involved in regulating related phenomena (Jiang et al., 2021). Several studies in past years have helped determining the TFs’ binding sites via sev- eral in vitro and in vivo techniques (Harbison et al., 2004; Riechmann, 2000). It was reported that 5% of the Arabidopsis thaliana genome codes for more than 1500 TFs, classified into different families based on structural and domain arrangement. Each TF can bind to several DNA fragments and regulate different processes simultaneously (Chen and Schmid, 2010). Light is a major developmental cue for plants perceived by photoreceptors, including phyto- chromes, cryptochromes, phototropins, and UVR8 (Cashmore et al., 1999; Rizzini et al., 2011; Briggs and Olney, 2001). These photoreceptors respond to different wavelengths of light and trans- mit the perceived signals via signaling cascade to TFs, which further regulate the light-mediated responses via modulating the target gene expression. These light-mediated responses include seed- ling photomorphogenesis, seed germination, shade avoidance, and photoperiod responses. Many light-responsive TFs have been identified based on the gene expression analysis of light-induced plant samples and genetic analyses of mutants that are deficient in their response to light (Jiao et al., 2007). 139 Plant Transcription Factors. DOI: https://doi.org/10.1016/B978-0-323-90613-5.00013-3 © 2023 Elsevier Inc. All rights reserved.