The ENHANCER OF SHOOT REGENERATION 2 gene in Arabidopsis regulates CUP-SHAPED COTYLEDON 1 at the transcriptional level and controls cotyledon development.

Cytokinins stimulate shoot regeneration in tissue culture but the genes required for this developmental process are not well understood. Here we show that the Arabidopsis gene, ENHANCER OF SHOOT REGENERATION 2 (ESR2), encoding an AP2-domain transcriptional factor, functions in the regeneration of shoots in tissue culture. ESR2 overexpression conferred cytokinin-independent shoot regeneration from cre1/ahk4 mutant explants, suggesting that CRE1 is not required for ESR2-mediated shoot regeneration. ESR2 directly targeted CYCLIN D1;1, ARABIDOPSIS PHOSPHOTRANSMITTER 6 (AHP6) and CUP-SHAPED COTYLEDON 1 (CUC1) in assays involving the translocation of ESR2-ER (estradiol receptor) fusions to the nucleus. Knock-down of ESR2 expression by RNA interference (RNAi) reduced CUC1 expression and resulted in altered cotyledon phenotypes at a low frequency, including partially fused cotyledons and triple cotyledons. Phenotypes of induced ESR2 expression in a cuc1-1 mutant background were suppressed. Our results suggest that ESR2 plays a role in shoot regeneration through transcriptional regulation of CUC1.