Immediate early induction of mRNAs for ethylene-responsive transcription factors in tobacco leaf strips after cutting

To investigate the functional relationship between the expression of genes for ethylene-responsive transcription factors (ERFs) and the expression of ethylene-responsive genes, we examined the expression of genes for ERFs and the expression of a reporter gene in transgenic tobacco that carried a gene for P-glucuronidase (GUS) under the control of the ethylene-responsive element, which includes four copies of the Il-bp consensus sequence (designated the GCC-box, TAAGAGCCGCC). In strips of leaves of transgenic tobacco, the GCC-box mediated expression of the reporter gene was induced in response to treatment with ethylene. We also observed the ethylene-independent immediate early induction of the synthesis of mRNAs for ERFs in wounded leaves and the enhancement of this induction by cycloheximide (CHX). Since CHX suppressed the induction of mRNAs for chitinase and GUS by ethylene, protein synthesis de novo was required for induction of the ethylene-dependent GCC-box-mediated transcription of genes. In contrast, the enhancement by CHX of the wound-induced expression of ERFs suggested that no synthesis of new proteins was required for the wounding signal transduction leading to rapid expression of ERFs. Methyl jasmonate did not stimulate the wounding-responsive accumulation of ERF mRMAs, but it reduced such accumulation of mRNAs for ERF1, ERF2, ERF4 and the ethylene-dependent GCC-box-mediated transcription of the reporter gene. Thus, the immediate early induction of the expression of genes for ERFs in strips of tobacco leaves appears to be a novel type of wound-responsive activation of transcription. These results suggested that the expression of ERFs was not sufficient for activation of the GCC-box-mediated transcription but the expression of ERF1, ERF2 and ERF4 and that conversion of these ERFs by ethylene to their active form might be crucial for the GCC-box-medated activation of the transcription of defense genes.