Ethylene Signaling Cascade: From Hormone Perception to Transcriptional Regulation

Abstract

Ethylene is a gaseous phytohormone that regulates diverse aspects of plant growth, development, and stress responses. Despite its simple chemical nature, ethylene activates a highly sophisticated signal transduction pathway that converts hormone perception into precise changes in gene expression. The study aims to comprehensively analyse the ethylene signal transduction pathway in plants, focusing on how ethylene perception is translated into molecular and genetic responses and the importance of ethylene signalling in regulating plant growth and stress responses. Ethylene signalling is initiated by membrane-bound receptors localised to the endoplasmic reticulum, which function as negative regulators in the absence of the hormone. The regulation of ethylene production occurs at multiple levels, including transcriptional, post-transcriptional, and post-translational control mechanisms. The ethylene signalling pathway comprises several core components: a family of endoplasmic reticulum (ER)-localised ethylene receptors; the protein kinase constitutive triple response 1 (CTR1); the ER-associated transmembrane protein ethylene-insensitive 2 (EIN2), whose biochemical activity remains unresolved; and nuclear transcription factors including EIN3, EIN3-like (EIL), and ethylene response factors (ERFs). Ethylene functions as an inverse agonist by inhibiting receptor activity, which reduces CTR1-mediated repression and permits EIN2 activation. EIN2 subsequently modulates transcriptional and translational processes, driving the majority of ethylene responses. While this canonical cascade represents the principal signalling route, additional non-canonical pathways also contribute to ethylene-regulated processes. Ethylene binding inactivates these receptors, leading to suppression of the downstream kinase CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) and activation of ETHYLENE INSENSITIVE 2 (EIN2). Subsequent nuclear signalling involves stabilisation of the transcription factors EIN3 and EIN3-LIKE (EIL), which regulate the expression of ethylene-responsive genes. This tightly regulated signalling cascade controls key physiological processes such as fruit ripening, senescence, abscission, and stress adaptation. Ethylene sensing depends on receptors such as ETR1 and ERS1, located on the endoplasmic reticulum. This review synthesizes current knowledge of ethylene signalling, highlights emerging alternative mechanisms, and examines strategies by which ethylene signalling has been exploited in agricultural and horticultural contexts.