bZIP and bHLH Family Members Integrate Transcriptional Responses to Light

Among many environmental factors influencing plant growth and development, light is one of the most challenging. Perception of light signals by an array of photoreceptors, including the phytochromes, leads to altered expression of thousands of genes that are instrumental in enabling the plant to respond at the metabolic and physiological level. These expression changes involve the participation of transcriptional regulators of different families that, in some cases, are fundamental for the implementation of the corresponding developmental program by integrating exogenous and endogenous signals. We will focus mainly on three of these transcriptional regulators: (1) PIFs (PHYTOCHROME INTERACTING FACTORs), which have a unique role as transcription factors linking light perception by phytochromes and changes in gene expression; (2) HFR1 (HYPOCOTYL IN FAR-RED LIGHT 1) and PAR1 (PHYTOCHROME RAPIDLY REGULATED 1), because of their regulatory role on PIFs as microproteins; and (3) HY5 (LONG HYPOCOTYL 5), a basic domain/leucine zipper (bZIP) transcription factor that integrates light responses in an antagonistic manner to PIFs.