Ethylene

Ethylene is the first-identified plant hormone known to regulate numerous processes in plant growth, development, and response to biotic and abiotic stresses. Ethylene is best known for its effect on fruit ripening and organ abscission, and thus has great commercial importance in agriculture. As a gaseous hormone, ethylene can freely diffuse across membranes and is thought to be synthesized at or near its site of action, which is different from other plant hormones. By use of the typical "triple response" phenotype, significant progresses have been made on ethylene metabolism, perception, and signaling in the past two decades. To summarize the major aspects of ethylene biology in plants, this chapter is mainly divided into three parts. Part one deals with ethylene biosynthesis and its regulation covering the well-known "Yang cycle" and the transcriptional and posttranslational regulation of related enzymes. Part two deals with ethylene perception and signaling in the model plant Arabidopsis, including the key components and main breakthroughs of ethylene signal transduction. Part three deals with the ethylene perception and signaling and the cross talk of ethylene with other hormones in rice. Finally, intriguing questions related to ethylene action are proposed, which need to be further addressed in the future.