The expanding roles of APETALA2/Ethylene Responsive Factors and their potential applications in crop improvement

Understanding the molecular basis of the gene-regulatory networks underlying agronomic traits or plant responses to abiotic/biotic stresses is very important for crop improvement. In this context, transcription factors, which either singularly or in conjugation directly control the expression of many target genes, are suitable candidates for improving agronomic traits via genetic engineering. In this regard, members of one of the largest class of plant-specific APETALA2/Ethylene Response Factor (AP2/ERF) superfamily, which is implicated in various aspects of development and plant stress adaptation responses, are considered high-value targets for crop improvement. Besides their long-known regulatory roles in mediating plant responses to abiotic stresses such as drought and submergence, the novel roles of AP2/ERFs during fruit ripening or secondary metabolites production have also recently emerged. The astounding functional plasticity of AP2/ERF members is considered to be achieved by their interplay with other regulatory networks and signalling pathways. In this review, we have integrated the recently accumulated evidence from functional genomics studies and described their newly emerged functions in plants. The key structural features of AP2/ERF proteins and the modes of their action are briefly summarized. The importance of AP2/ERFs in plant development and stress responses and a summary of the event of their successful applications in crop improvement programs are also provided. Altogether, we envisage that the synthesized information presented in this review will be useful to design effective strategies for improving agronomic traits in crop plants.