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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.
Ikeda et al. (Sat,) studied this question.