Structure and Evolution of Plant Homeobox Genes

Homeobox genes constitute a large family of eukaryotic genes that encode the transcription factors involved in the regulation of developmental processes. The homeobox encodes a highly conserved DNA-binding domain, the homeodomain, which folds into a three-helix structure with similarities to the helix–turn–helix motifs of prokaryotic transcription factors. Homeodomain proteins are classified into different families and subfamilies according to sequence conservation and the presence of additional motifs besides the homeodomain. Interestingly, although present in most eukaryotic organisms, a majority of plant homeodomain families are unique to plants, suggesting that they have evolved to fulfill specific aspects of plant developmental processes. In this chapter the structure of homeodomains and the way they establish specific contacts with DNA are described. The distinctive features of plant homeodomains are also discussed, together with an overview of the evolutionary history of these proteins.