Figure 8.

Nuclear events in the ethylene gas signaling pathway. Model depicts the transcriptional regulatory cascade that mediates ethylene responses. Binding of ethylene (C₂H₄) to membrane receptors activates EIN3, and most likely EIL1 and EIL2, through a signaling cascade described elsewhere (Chao et al. 1997). EIN3 directs the expression of ERF1 and other primary target genes by binding directly, as a dimer to the E4-like PERE present in their promoters. ERF1 and probably other EREBPs bind to the GCC box (SERE) and activate the expression of secondary ethylene response genes such as basic-chitinase and defensin (PDF1.2). Although we favor this simple model, the results presented in this work do not exclude other more complicated models that may involve the existence of an intermediate between EIN3 and ERF1 or the existence of EIN3-interacting proteins that modulate EIN3 activity.