Identification of ENHANCER OF SHOOT REGENERATION 1-upregulated genes during in vitro shoot regeneration

The Arabidopsis ENHANCER OF SHOOT REGENERATION 1 (ESR1) is thought to be a key gene for commitment to in vitro shoot regeneration in tissue culture. ESR1 encodes a member of the ETHYLENE RESPONSIVE FACTOR (ERF) family of transcription factors. Here, we report identification of genes downstream of ESR1 during in vitro shoot regeneration. We previously demonstrated that the ESR1 protein functions as a transcriptional activator; in the present study, genes upregulated after induction of ESR1 overexpression were screened by microarray experiments. Seven genes, including CUP-SHAPED COTYLEDON 1 (CUC1), CLAVAT3/EMBRYO SURROUNDING REGION-RELATED PEPTIDE 2 (CLE2), and GCN5-relaled N-acetyltransferase 1 (GNAT1) were identified as ESR1-upregulated genes by screening. CUC1, CLE2, and GNAT1 were also upregulated by translocation of ESR1-ER (estrogen receptor) fusions to the nucleus in the presence of cycloheximide, suggesting that these genes are possibly the direct target of the ESR1 protein. Transcript levels of CUC1, CLE2, and GNAT1 as well as ESR1 increased during the early in vitro shoot regeneration process, although their time courses were not necessarily similar. Thus, these genes may function downstream of ESR1 and may be involved in the shoot differentiation process.