The ethylene pathway: a paradigm for plant hormone signaling and interaction

To dissect the web of signals that control plant growth, it is important to understand how the individual components of the pathway are modulated. Ethylene is a plant hormone involved in a large number of developmental processes. Biochemical and genetic approaches have provided a detailed view of the biosynthetic and signal transduction pathways of this hormone in the reference plant Arabidopsis thaliana. The effects of several hormones and of developmental changes on the regulation of the key enzymes of ethylene biosynthesis, ACC synthase and ACC oxidase, serve as a clear example of interaction between signals in the generation of complex responses. We now have a picture of how ethylene is sensed by the ethylene receptors and how the signal is further transduced to the nucleus. Although some of the ethylene receptors show a tissue-specific pattern of expression, little is known about the regulation of the components of the ethylene transduction cascade by other hormones or developmental factors. Once the ethylene signal reaches the nucleus, it activates a transcriptional cascade that results in changes in the expression of a number of genes. We describe some of the results that suggest an interaction at the transcriptional level between ethylene, other hormones, and stress signals.