Transcription factors (TFs) are proteins that regulate the expression of target genes by binding to specific cis-elements in promoter regions. Transcriptional regulators (TRs) also regulate the expression of target genes; however, they operate indirectly via interaction with the basal transcription apparatus (e.g., TFs), or by altering the accessibility of DNA to TFs via chromatin remodeling. Another type of regulatory proteins, protein kinases (PKs), function in signal transduction pathways and alter the activity of target proteins by phosphorylating them. These three important classes of regulatory proteins have been associated with numerous aspects of plant growth and development (Gapper et al., 2014; Xu and Zhang, 2015), and response to biotic and abiotic stimuli (Zhang et al., 2013; Mickelbart et al., 2015). Effective and accurate identification and classification of these genes is important for understanding their evolution, biological functions, and regulatory networks. Currently, more than 100 plant genomes have been sequenced and regulatory proteins have been systematically identified from several of these plant genomes.