A domain containing the ESR motif in ENHANCER OF SHOOT REGENERATION 1 functions as a transactivation domain

The Arabidopsis ENHANCER OF SHOOT REGENERATION 1 (ESR1) gene is thought to regulate the initiation of in vitro shoot regeneration. ESR1 encodes a transcriptional activator belonging to the ETHYLENE-RESPONSIVE FACTOR family. In this study, we investigated the functions of the C-terminal domain of the ESR1 protein. Effectorreporter assays using the GAL4 DNA-binding domain fused with portions of the C-terminal domain revealed that the ESR motif, which is a short amino acid sequence commonly seen in the C-terminal domain of ESR1 and ESR2, functions as a transactivation domain. We also examined the effects of partial deletions of the C-terminal domain on the in vitro shoot regeneration-enhancing effects of ESR1 overexpression. The results revealed that the ESR motif and a region between the AP2/ERF domain and the ESR motif were required for the shoot regeneration-enhancing effects of ESR1. The region between the AP2/ERF domain and the ESR motif appeared to have an essential function other than nuclear localization, DNA-binding, and transactivation. Substitution of the ESR motif by the VP16 transactivation domain abolished the ability of ESR1 to enhance shoot regeneration, suggesting that the ESR motif not only has transactivation activity but also has other functions.