ABSTRACT
Transcription factors (TFs) bind directly to the promoters of target genes in a sequence-specifi c manner to either activate or repress transcription. TFs carry out their function as part of multi-protein complexes; thus, proteins which do not by themselves bind DNA, but are part of multiprotein complexes that bind specifi c DNA sequences, are often considered to be TFs. Because of their central role in regulating gene expression, they are key components of most signal transduction pathways and regulate innumerable subcellular to organism-level biological processes. Moreover, changes in gene expression play a major role in phenotypic plasticity, variation within species, and divergence between species (Babu et al. 2004; Wittkopp 2007). Doebley and Lukens (1998) proposed that changes in the cis-regulatory elements of TFs represent a predominant mechanism for the evolution of plant form. Although the genes and mechanisms underlying plant phenotypic diversity are still largely unknown, considerable evidence supports that TFs are likely to have a major role. Most plant TFs are part of large, multi-gene families defi ned by the type of DNA-binding domain that they encode, and TF family or subfamily size can vary signifi cantly among plant taxa (Riechmann et al. 2000; Qu and Zhu 2006; Tuskan et al. 2006; Ming et al. 2008). Whole genome duplications have been prevalent in angiosperm evolution, and studies indicate that TFs have been preferentially retained following genome duplication (De Bodt et al. 2005; Shiu et al. 2005; Semon and Wolfe 2007).
