Homeodomain leucine-zipper proteins and their role in synchronizing growth and development with the environment

The Arabidopsis (Arabidopsis thaliana L.) genome encodes for four distinct classes of homeodomain leucine-zipper (HD-ZIP) transcription factors (HD-ZIPI to HD-ZIPIV), which are all organized in multi-gene families. HD-ZIP transcription factors act as sequence-specific DNA-binding proteins that are able to control the expression level of target genes. While HD-ZIPI and HD-ZIPII proteins are mainly associated with environmental responses, HD-ZIPIII and HD-ZIPIV are primarily known to act as patterning factors. Recent studies have challenged this view. It appears that several of the different HD-ZIP families interact genetically to align both morphogenesis and environmental responses, most likely by modulating phytohormone-signaling networks.