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Authors: Oluwaseun Olayemi Aluko, Vincent Ninkuu, James Ziemah, Yan Jianpei, Esther Taiwo, Stephen Bright Ninkuu, Noah Sabuli, Adetunde Lawrence Adelani, Abdul-Wahab M. Imoru, Suleiman Fatimoh Ozavize, Queen Adaugo Onyiro, Godfred Dogee, Oluwafemi Michael Adedire, Oluwaseyi Setonji Hunpatin and Nelson Opoku.
Plant Stress (2024)
Highlights: • Ethylene-insensitive3/ethylene-insensitive3-like (EIN3/EILs) proteins in rice exhibit three clads in a Maximum Likelihood (ML) tree. • The gene structures and motif composition of EIN3/EILs genes suggest potential stress-mitigation functions. • OsEIN3/EILs genes are responsive to exogenous abscisic acid and jasmonic acid treatment, highlighting their potential role in growth mediation and abiotic stress tolerance • OsEIN3/EILs genes are highly responsive to drought and salt stresses
Abstract: "The nuclear-localized ethylene-insensitive3/ethylene-insensitive3-like (EIN3/EIL) proteins regulate the ethylene signaling pathway for growth and stress responses. This study presents a genome-wide analysis of nine Oryza sativa EIN3/EIL genes, exhibiting three clads in an ML phylogenetic tree. These proteins are conserved in both exon-intron organization and motif architecture aligned with their phylogenetic clustering. The EIN3/EIL proteins harbor the EIN3, EIN3 superfamily, and RDV-p3 conserved domains. OsEIN3/EIL expression profiling revealed consistently high transcript levels of LOC_Os03g20790 and LOC_Os02g36510 in leaf blades across vegetative and reproductive stages and in the endosperm, indicating a potential role in growth and yield enhancement. Additionally, LOC_Os03g20790, LOC_Os02g36510, LOC_Os07g48630, and LOC_Os09g31400 are highly expressed at later stages of root development, showing potential in nutrient signaling for seed-filling. Moreover, elevated expression of LOC_Os04g38400, LOC_Os09g31400, LOC_Os03g20790, LOC_Os08g39830, and LOC_Os07g48630 were detected under mannitol treatment, while LOC_Os04g38400 and LOC_Os08g39830 were highly upregulated in root and leaf tissues under drought stress exposure. Additionally, EIN3/EIL genes intricately interacted with MPK1, MPK5, and MYC genes, underscoring their potential involvement in growth and stress tolerance. Our findings lay a foundation for improved rice growth and yield enhancement."
Authors: Jian-Jun Tao, Cui-Cui Yin, Yang Zhou, Yi-Hua Huang, Shou-Yi Chen and Jin-Song Zhang.
Environmental and Experimental Botany (2024)
Highlights: • Universal and divergent functions of ethylene in different crops under salinity. • The opposite role of ethylene signaling in rice compared to some other crops. • The dual roles of ethylene being a stress signal and a stress substance.
Abstract: "Soil salinization severely hinders plant growth and decreases crop yield, and is increasingly an obstacle for the sustainability of agriculture. As a stress hormone, ethylene is known to function as a signal molecule to coordinate plant growth and stress response in the dicotyledonous model plant Arabidopsis. However, the roles of ethylene in most crop plants under salinity have received less attention, and underlying mechanisms are still undefined. According to reported results, the functions of ethylene as a stress signal in some crop species like the semiaquatic monocotyledonous plant rice turn out to be much different. Moreover, there exist some contradictions between ethylene production and signaling in salt response. Therefore, in this review, besides making a summary of the universal roles, we also focus on the divergent roles of ethylene under salinity in rice and some other crop species, in terms of ethylene biosynthesis and signal transduction. In addition, the discrepancies between ethylene production and signaling in salt response are discussed."
Authors: Qinpei Li, Haiqi Fu, Xiang Yu, Xing Wen, Hongwei Guo, Yan Guo and Jingrui Li.
Journal of Experimental Botany (2023)
Abstract: "High salinity stress promotes plant ethylene biosynthesis and triggers the ethylene signaling response. However, the precise mechanism underlying how plants transduce ethylene signaling in response to salt stress remains largely unknown. In this study, we discovered that SALT OVERLY SENSITIVE 2 (SOS2) inhibits the kinase activity of CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) by phosphorylating the 87th serine (S87). This phosphorylation event activates the ethylene signaling response, leading to enhanced plant salt resistance. Furthermore, through genetic analysis, we determined that the loss of CTR1 or the gain of SOS2-mediated CTR1 phosphorylation both contribute to improved plant salt tolerance. Additionally, in the sos2 mutant, we observed compromised proteolytic processing of ETHYLENE INSENSITIVE 2 (EIN2) and reduced nuclear localization of EIN2 C-terminal fragments (EIN2-C), which correlates with decreased accumulation of ETHYLENE INSENSITIVE 3 (EIN3). Collectively, our findings unveil the role of the SOS2-CTR1 regulatory module in promoting the activation of the ethylene signaling pathway and enhancing plant salt tolerance."
Authors: Kirti Shekhawat, Katja Fröhlich, Gabriel X. García-Ramírez, Marilia A. Trapp and Heribert Hirt.
Cells (2023)
Abstract: "The plant phytohormone ethylene regulates numerous physiological processes and contributes to plant–microbe interactions. Plants induce ethylene production to ward off pathogens after recognition of conserved microbe-associated molecular patterns (MAMPs). However, plant immune responses against pathogens are essentially not different from those triggered by neutral and beneficial microbes. Recent studies indicate that ethylene is an important factor for beneficial plant–microbial association under abiotic stress such as salt and heat stress. The association of beneficial microbes with plants under abiotic stresses modulates ethylene levels which control the expression of ethylene-responsive genes (ERF), and ERFs further regulate the plant transcriptome, epi-transcriptome, Na+/K+ homeostasis and antioxidant defense mechanisms against reactive oxygen species (ROS). Understanding ethylene-dependent plant–microbe interactions is crucial for the development of new strategies aimed at enhancing plant tolerance to harsh environmental conditions. In this review, we underline the importance of ethylene in beneficial plant–microbe interaction under abiotic stresses."
Authors: Qian Ma, Chunxue Su and Chun-Hai Dong.
Plants (2021)
Abstract: "Quinoa (Chenopodium quinoa Willd.), originated from the Andean region of South America, shows more significant salt tolerance than other crops. To reveal how the plant hormone ethylene is involved in the quinoa responses to salt stress, 4-week-old quinoa seedlings of ‘NL-6′ treated with water, sodium chloride (NaCl), and NaCl with ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were collected and analyzed by transcriptional sequencing and tandem mass tag-based (TMT) quantitative proteomics. A total of 9672 proteins and 60,602 genes was identified. Among them, the genes encoding glutathione S-transferase (GST), peroxidase (POD), phosphate transporter (PT), glucan endonuclease (GLU), beta-galactosidase (BGAL), cellulose synthase (CES), trichome birefringence-like protein (TBL), glycine-rich cell wall structural protein (GRP), glucosyltransferase (GT), GDSL esterase/lipase (GELP), cytochrome P450 (CYP), and jasmonate-induced protein (JIP) were significantly differentially expressed. Further analysis suggested that the genes may mediate through osmotic adjustment, cell wall organization, reactive oxygen species (ROS) scavenging, and plant hormone signaling to take a part in the regulation of quinoa responses to ethylene and salt stress. Our results provide a strong foundation for exploration of the molecular mechanisms of quinoa responses to ethylene and salt stress."
Authors: Xiao Zou, Li Liu, Zhubing Hu, Xuekui Wang, Yanchun Zhu, Jialiang Zhang, Xuefei Li, Ziyi Kang, Yongjun Lin and Changxi Yin.
Journal of Experimental Botany (2021)
Abstract: "The phytohormones ethylene and jasmonate play important roles in the adaption of rice plants to salt stress. However, the molecular interactions between ethylene and jasmonate on rice seminal root growth under salt stress is unknown. In this study, effects of NaCl on the homeostasis of ethylene and jasmonate and on the rice seminal root growth were investigated. Our results indicate that NaCl treatment promotes ethylene biosynthesis by up-regulating transcription of ethylene biosynthesis genes, whereas NaCl-induced ethylene cannot inhibit rice seminal root growth directly, but rather inhibits growth indirectly by promoting jasmonate biosynthesis. NaCl treatment also promotes jasmonate biosynthesis through an ethylene-independent pathway. Moreover, the analysis results of quantitative real-time PCR and confocal microscopy demonstrate that NaCl-induced jasmonate restricts root meristem cell proliferation by reducing meristem cell number and cell division activity via down-regulated transcription of OsPLT and cell division-related genes, respectively. Additionally, NaCl-induced jasmonate inhibits root cell elongation by down-regulating transcription of cell elongation-related genes, which in turn inhibits seminal root growth. Overall, salt stress promotes jasmonate biosynthesis through ethylene-dependent and -independent pathways in the rice seminal root, and salt-induced jasmonate inhibits the rice seminal root growth by inhibiting root meristem cell proliferation and root cell elongation under salt stress."
Authors: Irina I. Vaseva, Kiril Mishev, Thomas Depaepe, Valya Vassileva and Dominique Van Der Straeten.
Plants (2021)
Abstract: "We explored the interplay between ethylene signals and the auxin pool in roots exposed to high salinity using Arabidopsis thaliana wild-type plants (Col-0), and the ethylene-signaling mutants ctr1-1 (constitutive) and ein2-1 (insensitive). The negative effect of salt stress was less pronounced in ctr1-1 individuals, which was concomitant with augmented auxin signaling both in the ctr1-1 controls and after 100 mM NaCl treatment. The R2D2 auxin sensor allowed mapping this active auxin increase to the root epidermal cells in the late Cell Division (CDZ) and Transition Zone (TZ). In contrast, the ethylene-insensitive ein2-1 plants appeared depleted in active auxins. The involvement of ethylene/auxin crosstalk in the salt stress response was evaluated by introducing auxin reporters for local biosynthesis (pTAR2::GUS) and polar transport (pLAX3::GUS, pAUX1::AUX1-YFP, pPIN1::PIN1-GFP, pPIN2::PIN2-GFP, pPIN3::GUS) in the mutants. The constantly operating ethylene-signaling pathway in ctr1-1 was linked to increased auxin biosynthesis. This was accompanied by a steady expression of the auxin transporters evaluated by qRT-PCR and crosses with the auxin transport reporters. The results imply that the ability of ctr1-1 mutant to tolerate high salinity could be related to the altered ethylene/auxin regulatory loop manifested by a stabilized local auxin biosynthesis and transport."
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Authors: Petar Mohorović, Batist Geldhof, Kristof Holsteens, Marilien Rinia, Johan Ceusters and Bram Van de Poel.
Plant Direct (2023)
Abstract: "Salinity, drought, and waterlogging are common environmental stresses that negatively impact plant growth, development, and productivity. One of the responses to abiotic stresses is the production of the phytohormone ethylene, which induces different coping mechanisms that help plants resist or tolerate stress. In this study, we investigated if an ethylene pretreatment can aid plants in activating stress-coping responses prior to the onset of salt, drought, and waterlogging stress. Therefore, we measured real-time transpiration and CO2 assimilation rates and the impact on biomass during and after 3 days of abiotic stress. Our results showed that an ethylene pretreatment of 1 ppm for 4 h did not significantly influence the negative effects of waterlogging stress, while plants were more sensitive to salt stress as reflected by enhanced water losses due to a higher transpiration rate. However, when exposed to drought stress, an ethylene pretreatment resulted in reduced transpiration rates, reducing water loss during drought stress. Overall, our findings indicate that pretreating tomato plants with ethylene can potentially regulate their responses during the forthcoming stress period, but optimization of the ethylene pre-treatment duration, timing, and dose is needed. Furthermore, it remains tested if the effect is related to the stress duration and severity and whether an ethylene pretreatment has a net positive or negative effect on plant vigor during stress recovery. Further investigations are needed to elucidate the mode of action of how ethylene priming impacts subsequent stress responses."
Authors: Liuchun Feng, Qi Li, Dongqin Zhou, Mingyun Jia, Zhuangzhuang Liu, Zhaoqi Hou, Quanjin Ren, Shengdong Ji, Shifei Sang, Shipeng Lu and Jinping Yu.
The Plant Journal (2024)
Significance Statement: The utilization of plant growth-promoting rhizobacteria (PGPR) is an effective strategy for enhancing plant salt tolerance, but only a few mechanisms involved in this process have been identified so far. The present study showed methionine induced by Bacillus subtilis CNBG-PGPR-1 is a key regulator to enhance plant salt tolerance through the ethylene pathway and ROS scavenging, providing a novel understanding of the mechanism by which beneficial microbes improve plant salt tolerance.
Abstract: "Soil salinity severely threatens plant growth and crop yields. The utilization of PGPR is an effective strategy for enhancing plant salt tolerance, but the mechanisms involved in this process have rarely been reported. In this study, we investigated the effects of Bacillus subtilis CNBG-PGPR-1 on improving plant salt tolerance and elucidated the molecular pathways involved. The results showed that CNBG-PGPR-1 significantly improved the cellular homeostasis and photosynthetic efficiency of leaves and reduced ion toxicity and osmotic stress caused by salt in tomato. Transcriptome analysis uncovered that CNBG-PGPR-1 enhanced plant salt tolerance through the activation of complex molecular pathways, with plant hormone signal transduction playing an important role. Comparative analysis and pharmacological experiments confirmed that the ethylene pathway was closely related to the beneficial effect of CNBG-PGPR-1 on improving plant salt tolerance. Furthermore, we found that methionine, a precursor of ethylene synthesis, significantly accumulated in response to CNBG-PGPR-1 in tomato. Exogenous L-methionine largely mimicked the beneficial effects of CNBG-PGPR-1 and activated the expression of ethylene pathway-related genes, indicating CNBG-PGPR-1 induces methionine accumulation to regulate the ethylene pathway in tomato. Finally, CNBG-PGPR-1 reduced salt-induced ROS by activating ROS scavenger-encoding genes, mainly involved in GSH metabolism and POD-related genes, which were also closely linked to methionine metabolism. Overall, our studies demonstrate that CNBG-PGPR-1-induced methionine is a key regulator in enhancing plant salt tolerance through the ethylene pathway and ROS scavenging, providing a novel understanding of the mechanism by which beneficial microbes improve plant salt tolerance."
Authors: Hye Lin Park, Dong Hye Seo, Han Yong Lee, Arkadipta Bakshi, Chanung Park, Yuan-Chi Chien, Joseph J. Kieber, Brad M. Binder and Gyeong Mee Yoon.
Nature Communications (2023)
Editor's view: Park et al. show that upon exposure to ethylene gas, CTR1, which normally has a negative effect on ethylene signaling, translocates into the nucleus and enhances the plant’s response to ethylene by stabilizing the EIN3 transcription factor.
Abstract: "The phytohormone ethylene controls plant growth and stress responses. Ethylene-exposed dark-grown Arabidopsis seedlings exhibit dramatic growth reduction, yet the seedlings rapidly return to the basal growth rate when ethylene gas is removed. However, the underlying mechanism governing this acclimation of dark-grown seedlings to ethylene remains enigmatic. Here, we report that ethylene triggers the translocation of the Raf-like protein kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1), a negative regulator of ethylene signaling, from the endoplasmic reticulum to the nucleus. Nuclear-localized CTR1 stabilizes the ETHYLENE-INSENSITIVE3 (EIN3) transcription factor by interacting with and inhibiting EIN3-BINDING F-box (EBF) proteins, thus enhancing the ethylene response and delaying growth recovery. Furthermore, Arabidopsis plants with enhanced nuclear-localized CTR1 exhibited improved tolerance to drought and salinity stress. These findings uncover a mechanism of the ethylene signaling pathway that links the spatiotemporal dynamics of cellular signaling components to physiological responses."
Authors: Aung Htay Naing, Jova Riza Campol, Hyunhee Kang, Junping Xu, Mi Young Chung and Chang Kil Kim.
Frontiers in Plant Science (2022)
Abstract: "Ethylene plays a critical signaling role in the abiotic stress tolerance mechanism. However, the role of ethylene in regulating abiotic stress tolerance in petunia has not been well-investigated, and the underlying molecular mechanism by which ethylene regulates abiotic stress tolerance is still unknown. Therefore, we examined the involvement of ethylene in salt and drought stress tolerance of petunia using the petunia wild type cv. “Mirage Rose” and the ethylene biosynthesis genes (PhACO1 and PhACO3)-edited mutants (phaco1 and phaco3). Here, we discovered that editing PhACO1 and PhACO3 reduced ethylene production in the mutants, and mutants were more sensitive to salt and drought stress than the wild type (WT). This was proven by the better outcomes of plant growth and physiological parameters and ion homeostasis in WT over the mutants. Molecular analysis revealed that the expression levels of the genes associated with antioxidant, proline synthesis, ABA synthesis and signaling, and ethylene signaling differed significantly between the WT and mutants, indicating the role of ethylene in the transcriptional regulation of the genes associated with abiotic stress tolerance. This study highlights the involvement of ethylene in abiotic stress adaptation and provides a physiological and molecular understanding of the role of ethylene in abiotic stress response in petunia. Furthermore, the finding alerts researchers to consider the negative effects of ethylene reduction on abiotic stress tolerance when editing the ethylene biosynthesis genes to improve the postharvest quality of horticultural crops."
Authors: Irina I. Vaseva, Lyudmila Simova-Stoilova, Elisaveta Kirova, Kiril Mishev, Thomas Depaepe, Dominique Van Der Straeten and Valya Vassileva.
Plant Physiology and Biochemistry (2021)
Highlights • ctr1-1 mutant has high peroxidase activity under control and salt stress conditions. • P5CS activity differs in ein2-1 and ctr1-1 genetic background. • Salt stress induces high L-proline accumulation in ctr1-1 plants. • Salt hypersensitivity of ein2-1 is linked to suppressed SOS gene expression.
Abstract: "To pinpoint ethylene-mediated molecular mechanisms involved in the adaptive response to salt stress we conducted a comparative study of Arabidopsis thaliana wild type (Col-0), ethylene insensitive (ein2-1), and constitutive signaling (ctr1-1) mutant plants. Reduced germination and survival rates were observed in ein2-1 plants at increasing NaCl concentrations. By contrast, ctr1-1 mutation conferred salt stress tolerance during early vegetative development, corroborating earlier studies. Аll genotypes experienced strong stress as evidenced by the accumulation of reactive oxygen species (ROS) and increased membrane lipid peroxidation. However, the isoenzyme profiles of ROS scavenging enzymes demonstrated a higher peroxidase (POX) activity in ctr1-1 individuals under control and salt stress conditions. A markedly elevated free L-Proline (L-Pro) content was detected in the ethylene constitutive mutant. This coincided with the increased levels of Delta-1-Pyrroline-5-Carboxylate Synthase (P5CS) which is the rate-limiting enzyme from the proline biosynthetic pathway. A stabilized upregulation of a stress-induced P5CS1 splice variant was observed in the ctr1-1 background, which was not documented in the ethylene insensitive mutant ein2-1. Transcript profiling of the major SALT OVERLY SENSITIVE (SOS) pathway players (SOS1, SOS2, and SOS3) revealed altered gene expression in the organs of the ethylene signaling mutants. Overall suppressed SOS expression was observed in the ein2-1 mutants while only the SOS transcript profiles in the ctr1-1 roots were similar to the wild type. Altogether, we provide experimental evidence for ethylene-mediated molecular mechanisms implicated in the acclimation response to salt stress in Arabidopsis, which operate mainly through the regulation of free proline accumulation and enhanced ROS scavenging."
Authors: Gustavo Cebrián, Jessica Iglesias-Moya, Alicia García, Javier Martínez, Jonathan Romero, José Javier Regalado, Cecilia Martínez, Juan Luis Valenzuela and Manuel Jamilena.
Horticulture Research (2021)
Abstract: "Abiotic stresses have a negative effect on crop production, affecting both vegetative and reproductive development. Ethylene plays a relevant role in plant response to environmental stresses, but the specific contribution of ethylene biosynthesis and signalling components in the salt stress response differs between Arabidopsis and rice, the two most studied model plants. In this paper, we study the effect of three gain-of-function mutations affecting the ethylene receptors CpETR1B, CpETR1A, and CpETR2B of Cucurbita pepo on salt stress response during germination, seedling establishment, and subsequent vegetative growth of plants. The mutations all reduced ethylene sensitivity, but enhanced salt tolerance, during both germination and vegetative growth, demonstrating that the three ethylene receptors play a positive role in salt tolerance. Under salt stress, etr1b, etr1a, and etr2b germinate earlier than WT, and the root and shoot growth rates of both seedlings and plants were less affected in mutant than in WT. The enhanced salt tolerance response of the etr2b plants was associated with a reduced accumulation of Na+ in shoots and leaves, as well as with a higher accumulation of compatible solutes, including proline and total carbohydrates, and antioxidant compounds, such as anthocyanin. Many membrane monovalent cation transporters, including Na+/H+ and K+/H+ exchangers (NHXs), K+ efflux antiporters (KEAs), high-affinity K+ transporters (HKTs), and K+ uptake transporters (KUPs) were also highly upregulated by salt in etr2b in comparison with WT. In aggregate, these data indicate that the enhanced salt tolerance of the mutant is led by the induction of genes that exclude Na+ in photosynthetic organs, while maintaining K+/Na+ homoeostasis and osmotic adjustment. If the salt response of etr mutants occurs via the ethylene signalling pathway, our data show that ethylene is a negative regulator of salt tolerance during germination and vegetative growth. Nevertheless, the higher upregulation of genes involved in Ca2+ signalling (CpCRCK2A and CpCRCK2B) and ABA biosynthesis (CpNCED3A and CpNCED3B) in etr2b leaves under salt stress likely indicates that the function of ethylene receptors in salt stress response in C. pepo can be mediated by Ca2+ and ABA signalling pathways."
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