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1. Subcellular dynamics of ethylene signaling drive plant plasticity to growth and stress: Spatiotemporal control of ethylene signaling in Arabidopsis

   https://doi.org/10.1002/bies.202400043  

   Chien, Yuan‐Chi; Yoon, Gyeong_Mee (April 2024, BioEssays)

   Abstract Volatile compounds, such as nitric oxide and ethylene gas, play a vital role as signaling molecules in organisms. Ethylene is a plant hormone that regulates a wide range of plant growth, development, and responses to stress and is perceived by a family of ethylene receptors that localize in the endoplasmic reticulum. Constitutive Triple Response 1 (CTR1), a Raf‐like protein kinase and a key negative regulator for ethylene responses, tethers to the ethylene receptors, but undergoes nuclear translocation upon activation of ethylene signaling. This ER‐to‐nucleus trafficking transforms CTR1 into a positive regulator for ethylene responses, significantly enhancing stress resilience to drought and salinity. The nuclear trafficking of CTR1 demonstrates that the spatiotemporal control of ethylene signaling is essential for stress adaptation. Understanding the mechanisms governing the spatiotemporal control of ethylene signaling elements is crucial for unraveling the system‐level regulatory mechanisms that collectively fine‐tune ethylene responses to optimize plant growth, development, and stress adaptation. 

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2. A role for ethylene signaling and biosynthesis in regulating and accelerating CO₂ ‐ and abscisic acid‐mediated stomatal movements in Arabidopsis

   https://doi.org/10.1111/nph.18918  

   Azoulay‐Shemer, Tamar; Schulze, Sebastian; Nissan‐Roda, Dikla; Bosmans, Krystal; Shapira, Or; Weckwerth, Philipp; Zamora, Olena; Yarmolinsky, Dmitry; Trainin, Taly; Kollist, Hannes; et al (April 2023, New Phytologist)

   Summary Little is known about long‐distance mesophyll‐driven signals that regulate stomatal conductance. Soluble and/or vapor‐phase molecules have been proposed. In this study, the involvement of the gaseous signal ethylene in the modulation of stomatal conductance inArabidopsis thalianaby CO₂/abscisic acid (ABA) was examined.We present a diffusion model which indicates that gaseous signaling molecule/s with a shorter/direct diffusion pathway to guard cells are more probable for rapid mesophyll‐dependent stomatal conductance changes. We, therefore, analyzed different Arabidopsis ethylene‐signaling and biosynthesis mutants for their ethylene production and kinetics of stomatal responses to ABA/[CO₂]‐shifts.According to our research, higher [CO₂] causes Arabidopsis rosettes to produce more ethylene. An ACC‐synthase octuple mutant with reduced ethylene biosynthesis exhibits dysfunctional CO₂‐induced stomatal movements. Ethylene‐insensitive receptor (gain‐of‐function),etr1‐1andetr2‐1, and signaling,ein2‐5andein2‐1, mutants showed intact stomatal responses to [CO₂]‐shifts, whereas loss‐of‐function ethylene receptor mutants, includingetr2‐3;ein4‐4;ers2‐3,etr1‐6;etr2‐3andetr1‐6, showed markedly accelerated stomatal responses to [CO₂]‐shifts. Further investigation revealed a significantly impaired stomatal closure to ABA in the ACC‐synthase octuple mutant and accelerated stomatal responses in theetr1‐6;etr2‐3, andetr1‐6, but not in theetr2‐3;ein4‐4;ers2‐3mutants.These findings suggest essential functions of ethylene biosynthesis and signaling components in tuning/accelerating stomatal conductance responses to CO₂and ABA. 

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3. Detection of Ethylene with Defined Metal Complexes: Strategies and Recent Advances

   https://doi.org/10.1002/anse.202200058  

   Jensen, Katrina_H; Michel, Brian_W (September 2022, Analysis & Sensing)

   Abstract Despite its relative simplicity, ethylene is an interesting molecule with wide‐ranging impact in modern chemistry and biology. Stemming from ethylene's role as a critical plant hormone, there has been significant effort to develop selective and sensitive molecular sensors for ethylene. Late transition metal complexes have played an important role in detection strategies due to ethylene's lack of structural complexity and limited reactivity. Two main approaches to ethylene detection are identified: (1) coordination‐based sensors, wherein ethylene binds reversibly to a metal center, and (2) activity‐based sensors, wherein ethylene undergoes a reaction at a metal center, resulting in the formation and destruction of covalent bonds. Herein, we describe the advantages and disadvantages of various approaches, and the challenges remaining for sensor development. 

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4. An ethylene biosynthesis enzyme controls quantitative variation in maize ear length and kernel yield

   https://doi.org/10.1038/s41467-021-26123-z  

   Ning, Qiang; Jian, Yinan; Du, Yanfang; Li, Yunfu; Shen, Xiaomeng; Jia, Haitao; Zhao, Ran; Zhan, Jimin; Yang, Fang; Jackson, David; et al (October 2021, Nature Communications)

   Abstract Maize ear size and kernel number differ among lines, however, little is known about the molecular basis of ear length and its impact on kernel number. Here, we characterize a quantitative trait locus,qEL7, to identify a maize gene controlling ear length, flower number and fertility.qEL7encodes 1-aminocyclopropane-1- carboxylate oxidase2 (ACO2), a gene that functions in the final step of ethylene biosynthesis and is expressed in specific domains in developing inflorescences. Confirmation ofqEL7by gene editing ofZmACO2leads to a reduction in ethylene production in developing ears, and promotes meristem and flower development, resulting in a ~13.4% increase in grain yield per ear in hybrids lines. Our findings suggest that ethylene serves as a key signal in inflorescence development, affecting spikelet number, floral fertility, ear length and kernel number, and also provide a tool to improve grain productivity by optimizing ethylene levels in maize or in other cereals. 

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5. Ethylene-independent modulation of root development by ACC via downregulation of WOX5 and group I CLE peptide expression

   https://doi.org/10.1073/pnas.2417735122  

   Mou, Wangshu; Khare, Ria; Polko, Joanna K; Taylor, Isaiah; Xu, Juan; Xue, Dawei; Benfey, Philip; Van_de_Poel, Bram; Chang, Caren; Kieber, Joseph J (February 2025, Proceedings of the National Academy of Sciences)

   In seed plants, the canonical role of 1-aminocyclopropane-1-carboxylic acid (ACC) is to serve as the precursor in the biosynthesis of the phytohormone ethylene, and indeed, ACC treatment is often used as a proxy for ethylene treatment. Increasing evidence suggests that ACC can also act independently of ethylene to regulate various aspects of plant growth and development. Here, we explore the effects of ACC onArabidopsis thalianaroot growth and the mechanisms by which it acts. ACC inhibits growth of the primary root inArabidopsisseedlings when ethylene signaling is blocked, which becomes evident after 36 h of treatment with ACC. This reduced root growth is in part the result of suppressed cell proliferation in the root meristem resulting from altered expression of a key regulator of stem cell niche activity, WOX5. ACC also promotes lateral root (LR) development, in contrast to ethylene, which inhibits LR formation. Transcriptomic analysis of roots revealed no significant changes in gene expression after 45 min or 4 h of ACC treatment, but longer treatment times revealed a large number of differentially expressed genes, including the downregulation of the expression of a small group of phylogenetically related CLE peptides. Reduced expression of these group 1 CLEs in response to ACC leads to the activation of a transcription factor, LBD18, which promotes LR development. These results suggest that ACC acts to modulate multiple aspects ofArabidopsisroot growth independently of ethylene via distinct transcriptional effects in the root meristem and LR precursor cells. 

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