Ectopic expression of an EAR motif deletion mutant of SlERF3 enhances tolerance to salt stress and Ralstonia solanacearum in tomato

Ethylene-responsive transcription factors (ERFs) bind specifically to cis-acting DNA regulatory elements such as GCC boxes and play an important role in the regulation of defense- and stress-related genes in plants. In contrast to other ERFs, class II ERFs contain an ERF-associated amphiphilic repression (EAR) domain and act as GCC-mediated transcriptional repressors. In this study, SlERF3, a class II ERF was isolated from tomato and characterized. To examine whether the EAR motif of class II ERF proteins participates in ERF-mediated functions in plants, the EAR domain was deleted to generate SlERF3 Delta RD. We show that SlERF3 Delta RD protein retains the character of a transcription factor and becomes a GCC-mediated transcriptional activator. Constitutive expression of full-length SlERF3 in tomato severely suppressed growth and, as a result, no transgenic plants were obtained. However, no apparent effects on growth and development of SlERF3 Delta RD transgenic plants were observed. Overexpression of SlERF3 Delta RD in transgenic tomato induced expression of pathogenesis-related protein genes such as PR1, PR2 and PR5, and enhanced tolerance to Ralstonia solanacearum. Furthermore, transgenic Arabidopsis and tomatoes constitutively expressing SlERF3 Delta RD exhibited reduced levels of membrane lipid peroxidation and enhanced tolerance to salt stress. In comparison with wild-type plants grown under stress conditions, transgenic SlERF3 Delta RD tomatoes produced more flowers, fruits, and seeds. This study illustrates a gene-enhancing tolerance to both biotic and abiotic stresses in transgenic plants with the deletion of a repressor domain. Our findings suggest that class II ERF proteins may find important use in crop improvement or genetic engineering to increase stress tolerance in plants.