Ethylene Biosynthesis, Perception, and Response

Abstract

This thematic issue surveys our current understanding of ethylene biosynthesis, perception, and response. Tremendous progress has been made in elucidating how this gaseous hormone functions from the molecular level to the whole-plant level. At the same time, a number of questions are unanswered and new questions are being raised, making ethylene a fascinating hormone for which much remains a mystery. Classically considered the ripening or stress hormone, ethylene is known for its dramatic and diverse effects on plant growth and development. Numerous processes involve the action of this volatile hormone, including fruit ripening, senescence, abscission, and adaptive responses to biotic and abiotic stresses. Many of ethylene s effects have been known for nearly a century, yet responses to this simple hydrocarbon continue to be uncovered and examined from new perspectives, as illustrated by several articles in this issue. Many important advances have been made in our understanding of both ethylene biosynthesis and ethylene signaling. Although the enzymatic steps of ethylene biosynthesis are well understood and form a simple biochemical pathway, it is now known that the regulation of this pathway is highly complex, involving multigene families activated by diverse stimuli and controlled at different levels. In ethylene signal transduction, the foundation for the molecular dissection of the pathway has been the isolation of mutants in Arabidopsis that display an altered seedling ‘‘triple-response’’ phenotype in response to ethylene treatment. The first few mutants led to the identification of key components of the signaling pathway in fairly rapid succession. These components formed a linear pathway starting with ethylene binding to the receptors and leading to the regulation of gene expression. While thus it appeared early on that the ethylene-signaling pathway was largely solved, exactly how the proteins in this unique collection signal to one another remains an important question. Recent discoveries in ethylene signaling have created a more complex picture by introducing genes and processes that regulate the pathway. In addition, the integration of ethylene biosynthesis and ethylene response into larger signaling networks involving cross-talk with numerous other signals (for example, jasmonic acid, gibberellic acid, abscisic acid, auxin, glucose, and light) is just beginning. The nine articles in this issue highlight many of the advances and novel insights attained in recent years and suggest future directions and challenges. The articles cover a range of topics and reflect the diverse roles that ethylene plays in plant growth and development. Because of the scope of this issue, Received: 19 2 2007; accepted: 21 2 2007; Online publication: 8 6 2007 *Corresponding author; e-mail: carenc@umd.edu J Plant Growth Regul (2007) 26:89–91 DOI: 10.1007/s00344-007-9003-x