Ethylene signaling in plants

Abstract

Ethylene is a gaseous phytohormone and the first of this hormone class to be discovered. It is the simplest olefin gas and is biosynthesized by plants to regulate plant development, growth, and stress responses via a well-studied signaling pathway. One of the earliest reported responses to ethylene is the triple response. This response is common in eudicot seedlings grown in the dark and is characterized by reduced growth of the root and hypocotyl, an exaggerated apical hook, and a thickening of the hypocotyl. This proved a useful assay for genetic screens and enabled the identification of many components of the ethylene-signaling pathway. These components include a family of ethylene receptors in the membrane of the endoplasmic reticulum (ER); a protein kinase, called constitutive triple response 1 (CTR1); an ER-localized transmembrane protein of unknown biochemical activity, called ethylene-insensitive 2 (EIN2); and transcription factors such as EIN3, EIN3-like (EIL), and ethylene response factors (ERFs). These studies led to a linear model, according to which in the absence of ethylene, its cognate receptors signal to CTR1, which inhibits EIN2 and prevents downstream signaling. Ethylene acts as an inverse agonist by inhibiting its receptors, resulting in lower CTR1 activity, which releases EIN2 inhibition. EIN2 alters transcription and translation, leading to most ethylene responses. Although this canonical pathway is the predominant signaling cascade, alternative pathways also affect ethylene responses. This review summarizes our current understanding of ethylene signaling, including these alternative pathways, and discusses how ethylene signaling has been manipulated for agricultural and horticultural applications.

Ethylene signaling in rice and Arabidopsis: New regulators and mechanisms

“…However, in Arabidopsis the histidine kinase activity of ETR1 has been found to play only minor roles in modulating ethylene signaling, suggesting that ethylene receptors function differently from canonical bacterial histidine kinase sensors (Wang et al, 2003; Hall et al, 2012). Based on current knowledge concerning Arabidopsis and rice, ethylene receptors may function through both CTR1‐dependent and CTR1‐independent pathways to output these signals (Binder, 2020).…”

“…In this model, ethylene is perceived by ethylene receptors at the endoplasmic reticulum (ER) membrane and transduced through CTR1 and EIN2. The signal is further amplified by the EIN3/EIL1‐mediated transcriptional activation cascade to activate the expression of ethylene‐response genes, triggering the ethylene response (Azhar et al, 2019; Binder, 2020). In the absence of ethylene binding, ethylene receptors may somehow activate the kinase activity of CTR1 (Hua and Meyerowitz, 1998), which subsequently phosphorylates the C‐terminal domain of EIN2 and prevents it from participating in signaling (Ju et al, 2012).…”

Plant Nitrilase Homologues in Fungi: Phylogenetic and Functional Analysis with Focus on Nitrilases in Trametes versicolor and Agaricus bisporus

“…The unstable aglycons released from glucosinolates also give rise to toxic products, among them phenylacetonitrile (PAN) or indole-3-acetonitrile (IAN) [ 12 ]. HCN can be also formed as a side product of the biosynthesis of the plant hormone ethylene (a key substance in plant signaling networks [ 13 ]). HCN reacts with L-cysteine to give β-CA [ 12 ].…”

Plants in the real world: An introduction to the JBC Reviews thematic series

“…The first gaseous hormone identified was ethylene (not NO/nitric oxide, as many plant biologists are quick to remind their biomedical friends). The review by Binder (9) summarizes how ethylene signaling in plants operates and how they contribute to plant growth and development, as well as stress responses. Plants also use many of the canonical signaling systems found in other organisms, but plants exploit ubiquitin-based systems to an extent not found in mammals.…”