Background: Changes in cis or trans regulatory regions are the major driving forces that underlie the evolution of gene expression.Transcription factors (TFs) are the main trans factors involved in transcriptional regulation.The expansion and divergence of TF gene families may play a key role in the evolution of gene regulatory networks.Although much work has been devoted to this issue, our understanding of the mechanisms of the evolution of gene regulatory networks after gene duplication is still limited, owing to the lack of information about DNA-binding targets for each TF in different cell types.