Promoted Ethylene Production Research Articles

Enhancing CO2 Electroreduction Precision to Ethylene and Ethanol: The Role of Additional Boron Catalytic Sites in Cu-Based Tandem Catalysts.

The electrocatalytic conversion of carbon dioxide (CO2) into valuable multicarbon (C2+) compounds offers a promising approach to mitigate CO2 emissions and harness renewable energy. However, achieving precise selectivity for specific C2+ products, such as ethylene and ethanol, remains a formidable challenge. This study shows that incorporating elemental boron (B) into copper (Cu) catalysts provides additional adsorption sites for *CO intermediates, enhancing the selectivity of desirable C2+ products. Additionally, using a nickel single-atom catalyst (Ni-SAC) as a *CO source increases local *CO concentration and reduces the hydrogen evolution reaction. In situ experiments and density functional theory (DFT) calculations reveal that surface-bound boron units adsorb and convert *CO more efficiently, promoting ethylene production, while boron within the bulk phase of copper influences charge transfer, facilitating ethanol generation. In a neutral electrolyte, the bias current density for ethylene production using the B-O-Cu2@Ni-SAC0.05 hybrid catalyst exceeded 300 mA cm-2, and that for ethanol production with B-O-Cu5@Ni-SAC0.2 surpassed 250 mA cm-2. This study underscores that elemental doping in Cu-based catalysts not only alters charge and crystalline phase arrangements at Cu sites but also provides additional reduction sites for coupling reactions, enabling the efficient synthesis of distinct C2+ products.

Methyl jasmonate activated regulatory module Ma14-3-3e-MbHLH130-MbACO13/MbACS7 promoting ethylene biosynthesis and fruit ripening in banana

Methyl jasmonate (MeJA), an important phytohormone, plays a vital role in many biological processes. However, its effect and mechanism in regulating ethylene synthesis and fruit ripening in banana remain unknown. In this research, we found that exogenous MeJA accelerated postharvest ripening of banana, which coincided with increased ethylene production and upregulation of MbACS7 and MbACO13 expression. MabHLH130 directly interacted with and stimulated the transcription of MbACS7 and MbACO13. Additionally, MabHLH130 interacted with Ma14-3-3e through the RHSSSP motif. Overexpression of either MabHLH130 or Ma14-3–3e in tomato promoted ethylene production and fruit ripening, and this effect was enhanced by exogenous MeJA treatment. Furthermore, the Ma14-3–3e-MabHLH130 interaction module activated MbACS7 and MbACO13 transcription, which was enhanced by exogenous MeJA treatment. Taken together, these results demonstrated that the MeJA-responsive Ma14-3–3e-MabHLH130-MbACS7/MbACO13 module promoted ethylene biosynthesis and fruit ripening in bananas, providing valuable genetic targets for breeding programs aimed at extending fruit shelf-life.

The transcription factor WRKY22 modulates ethylene biosynthesis and root development through transactivating the transcription of ACS5 and ACO5 in Arabidopsis.

The WRKY transcription factor (TF) genes form a large family in higher plants, with 72 members in Arabidopsis (Arabidopsis thaliana). The gaseous phytohormone ethylene (ET) regulates multiple physiological processes in plants. It is known that 1-aminocyclopropane-1-carboxylic acid (ACC) synthases (ACSs, EC 4.4.1.14) limit the enzymatic reaction rate of ethylene synthesis. However, whether WRKY TFs regulate the expression of ACSs and/or ACC oxidases (ACOs, EC 1.14.17.4) remains largely elusive. Here, we demonstrated that Arabidopsis WRKY22 positively regulated the expression of a few ACS and ACO genes, thus promoting ethylene production. Inducible overexpression of WRKY22 caused shorter hypocotyls without ACC treatment. A qRT-PCR screening demonstrated that overexpression of WRKY22 activates the expression of several ACS and ACO genes. The promoter regions of ACS5, ACS11, and ACO5 were also activated by WRKY22, which was revealed by a dual luciferase reporter assay. A follow-up chromatin immunoprecipitation coupled with quantitative PCR (ChIP-qPCR) and electrophoretic mobility shift assay (EMSA) showed that the promoter regions of ACS5 and ACO5 could be bound by WRKY22 directly. Moreover, wrky22 mutants had longer primary roots and more lateral roots than wild type, while WRKY22-overexpressing lines showed the opposite phenotype. In conclusion, this study revealed that WRKY22 acts as a novel TF activating, at least, the expression of ACS5 and ACO5 to increase ethylene synthesis and modulate root development.

The OsEIL1-OsWOX11 transcription factor module controls rice crown root development in response to soil compaction.

Optimizing the root architecture of crops is an effective strategy for improving crop yields. Soil compaction is a serious global problem that limits crop productivity by restricting root growth, but the underlying molecular mechanisms are largely unclear. Here, we show that ethylene stimulates rice (Oryza sativa) crown root development in response to soil compaction. First, we demonstrate that compacted soil promotes ethylene production and the accumulation of ETHYLENE INSENSITIVE 3-LIKE 1 (OsEIL1) in rice roots, stimulating crown root primordia initiation and development, thereby increasing crown root number in lower stem nodes. Through transcriptome profiling and molecular analyses, we reveal that OsEIL1 directly activates the expression of WUSCHEL-RELATED HOMEOBOX 11 (OsWOX11), an activator of crown root emergence and growth, and that OsWOX11 mutations delay crown root development, thus impairing the plant's response to ethylene and soil compaction. Genetic analysis demonstrates that OsWOX11 functions downstream of OsEIL1. In summary, our results demonstrate that the OsEIL1-OsWOX11 module regulates ethylene action during crown root development in response to soil compaction, providing a strategy for the genetic modification of crop root architecture and grain agronomic traits.

The brassinosteroid signaling component SlBZR1 promotes tomato fruit ripening and carotenoid accumulation.

The plant hormone ethylene is essential for climacteric fruit ripening, although it is unclear how other phytohormones and their interactions with ethylene might affect fruit ripening. Here, we explored how brassinosteroids (BRs) regulate fruit ripening in tomato (Solanum lycopersicum) and how they interact with ethylene. Exogenous BR treatment and increased endogenous BR contents in tomato plants overexpressing the BR biosynthetic gene SlCYP90B3 promoted ethylene production and fruit ripening. Genetic analysis indicated that the BR signaling regulators Brassinazole-resistant1 (SlBZR1) and BRI1-EMS-suppressor1 (SlBES1) act redundantly in fruit softening. Knocking out SlBZR1 inhibited ripening through transcriptome reprogramming at the onset of ripening. Combined transcriptome deep sequencing and chromatin immunoprecipitation followed by sequencing identified 73 SlBZR1-repressed targets and 203 SlBZR1-induced targets involving major ripening-related genes, suggesting that SlBZR1 positively regulates tomato fruit ripening. SlBZR1 directly targeted several ethylene and carotenoid biosynthetic genes to contribute to the ethylene burst and carotenoid accumulation to ensure normal ripening and quality formation. Furthermore, knock-out of Brassinosteroid-insensitive2 (SlBIN2), a negative regulator of BR signaling upstream of SlBZR1, promoted fruit ripening and carotenoid accumulation. Taken together, our results highlight the role of SlBZR1 as a master regulator of tomato fruit ripening with potential for tomato quality improvement and carotenoid biofortification.

The microRNA ppe-miR393 mediates auxin-induced peach fruit softening by promoting ethylene production.

Auxin can inhibit or promote fruit ripening, depending on the species. Melting flesh (MF) peach fruit (Prunus persica L. Batsch) cultivars produce high levels of ethylene caused by high concentrations of indole-3-acetic acid (IAA), which leads to rapid fruit softening at the late stage of development. In contrast, due to the low concentrations of IAA, the fruit of stony hard (SH) peach cultivars does not soften and produces little ethylene. Auxin seems necessary to trigger the biosynthesis of ethylene in peach fruit; however, the mechanism is not well understood. In this study, we identified miRNA gene family members ppe-miR393a and ppe-miR393b that are differentially expressed in SH and MF fruits. RNA ligase-mediated 5' rapid amplification of cDNA ends and transient transformation of Nicotiana benthamiana revealed TRANSPORT INHIBITOR RESPONSE 1 (PpTIR1), part of the auxin perception and response system, as a target of ppe-miR393a and b. Yeast 2-hybrid assay and bimolecular fluorescence complementation assay revealed that PpTIR1 physically interacts with an Aux/IAA protein PpIAA13. The results of yeast 1-hybrid assay, electrophoretic mobility shift assay, and dual-luciferase assay indicated that PpIAA13 could directly bind to and trans-activate the promoter of 1-aminocyclopropane-1-carboxylic acid synthase 1 (PpACS1), required for ethylene biosynthesis. Transient overexpression and suppression of ppe-miR393a and PpIAA13 in peach fruit induced and repressed the expression of PpACS1, confirming their regulatory role in ethylene synthesis. Gene expression analysis in developing MF and SH fruits, combined with postharvest α-naphthalene acetic acid (NAA) treatment, supports a role for a ppe-miR393-PpTIR1-PpIAA13-PpACS1 module in regulating auxin-related differences in ethylene production and softening extent in different types of peach.

Suppression of the target of rapamycin kinase accelerates tomato fruit ripening through reprogramming the transcription profile and promoting ethylene biosynthesis.

Tomato fruit ripening is a unique process of nutritional and energy metabolism. Target of rapamycin (TOR), a conserved serine/threonine protein kinase in eukaryotes, controls cell growth and metabolism by integrating nutrient, energy, and hormone signals. However, it remains unclear whether TOR participates in the modulation of tomato fruit ripening. Here, we showed that the manipulation of SlTOR by chemical or genetic methods greatly alters the process of tomato fruit maturation. Expression pattern analysis revealed that the transcripts of SlTOR declined as fruit ripening progressed. Moreover, suppression of SlTOR by TOR inhibitor AZD8055 or knock down of its transcripts by inducible RNA interference, accelerated fruit ripening, and led to overall effects on fruit maturity, including changes in colour and metabolism, fruit softening, and expression of ripening-related genes. Genome-wide transcription analysis indicated that silencing SlTOR reprogrammed the transcript profile associated with ripening, including cell wall and phytohormone pathways, elevated the expression of ethylene biosynthetic genes, and further promoted ethylene production. In contrast, the ethylene action inhibitor 1-MCP efficiently blocked fruit maturation, even following SlTOR inhibition. These results suggest that accelerated fruit ripening caused by SlTOR inhibition depends on ethylene, and that SlTOR may function as a regulator in ethylene metabolism.

Methanol‐to‐Light Olefins Reaction using Zn‐Ag Modified SSZ‐13 Catalyst

AbstractThe 2 wt.% of Zn and Ag (Zn1‐x‐Agx; x=0.2, 0.4, 0.6 %) modified SSZ‐13 (SZ‐13) zeolite was prepared by wet‐impregnation method, and its catalytic activity was demonstrated for methanol‐to‐olefin (MTO). The Zn0.6‐Ag0.4/SZ‐13 catalyst exhibited high catalytic activity due to change in properties of catalyst. The Zn particles were highly dispersed inside the SZ‐13; while Ag particles were dispersed on the surface of SZ‐13, confirmed by HRTEM and surface area. The small % of Ag over SZ‐13 promotes ethylene production via aromatization of reaction, and highly dispersed Zn on SZ‐13 help to produce stable ethylene and propylene. The Zn0.6‐Ag0.4/SZ‐13 catalyst showed (∼10 %) higher light olefin (87 %) selectivity than parent SZ‐13 as well as mono metal incorporated SZ‐13. The higher catalytic activity was attributed due to effect of both metals (Zn and Ag), where Ag promotes partial aromatization on the surface, and Zn increases the Lewis acidity in the zeolite pore. This catalyst can help to improve the selectivity of light olefin using MTO reaction.

Increased ACS Enzyme Dosage Causes Initiation of Climacteric Ethylene Production in Tomato.

Fruits of wild tomato species show different ethylene-dependent ripening characteristics, such as variations in fruit color and whether they exhibit a climacteric or nonclimacteric ripening transition. 1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) are key enzymes in the ethylene biosynthetic pathway encoded by multigene families. Gene duplication is a primary driver of plant diversification and angiosperm evolution. Here, interspecific variations in the molecular regulation of ethylene biosynthesis and perception during fruit ripening in domesticated and wild tomatoes were investigated. Results showed that the activated ACS genes were increased in number in red-ripe tomato fruits than in green-ripe tomato fruits; therefore, elevated dosage of ACS enzyme promoted ripening ethylene production. Results showed that the expression of three ACS isogenes ACS1A, ACS2, and ACS4, which are involved in autocatalytic ethylene production, was higher in red-ripe tomato fruits than in green-ripe tomato fruits. Elevated ACS enzyme dosage promoted ethylene production, which corresponded to the climacteric response of red-ripe tomato fruits. The data suggest that autoinhibitory ethylene production is common to all tomato species, while autocatalytic ethylene production is specific to red-ripe species. The essential regulators Non-ripening (NOR) and Ripening-Inhibitor (RIN) have experienced gene activation and overlapped with increasing ACS enzyme dosage. These complex levels of transcript regulation link higher ethylene production with spatiotemporal modulation of gene expression in red-ripe tomato species. Taken together, this study shows that bursts in ethylene production that accompany fruit color changes in red-ripe tomatoes are likely to be an evolutionary adaptation for seed dispersal.

The miR164a-NAM3 module confers cold tolerance by inducing ethylene production in tomato.

Because of a high sensitivity to cold, both the yield and quality of tomato (Solanum lycopersicum L.) are severely restricted by cold stress. The NAC transcription factor (TF) family has been characterized as an important player in plant growth, development, and the stress response, but the role of NAC TFs in cold stress and their interaction with other post-transcriptional regulators such as microRNAs in cold tolerance remains elusive. Here, we demonstrated that SlNAM3, the predicted target of Sl-miR164a/b-5p, improved cold tolerance as indicated by a higher maximum quantum efficiency of photosystem II (Fv/Fm), lower relative electrolyte leakage, and less wilting in SlNAM3-overexpression plants compared to wild-type. Further genetic and molecular confirmation revealed that Sl-miR164a/b-5p functioned upstream of SlNAM3 by inhibiting the expression of the latter, thus playing a negative role in cold tolerance. Interestingly, this role is partially mediated by an ethylene-dependent pathway because either Sl-miR164a/b-5p silencing or SlNAM3 overexpression improved cold tolerance in the transgenic lines by promoting ethylene production. Moreover, silencing of the ethylene synthesis genes, SlACS1A, SlACS1B, SlACO1, and SlACO4, resulted in a significant decrease in cold tolerance. Further experiments demonstrated that NAM3 activates SlACS1A, SlACS1B, SlACO1, and SlACO4 transcription by directly binding to their promoters. Taken together, the present study identified the miR164a-NAM3 module conferring cold tolerance in tomato plants via the direct regulation of SlACS1A, SlACS1B, SlACO1, and SlACO4 expression to induce ethylene synthesis.

Post‐anthesis saline‐alkali stress inhibits grain filling by promoting ethylene production and signal transduction

AbstractSaline‐alkali stress is one of the major abiotic stresses that severely affect rice yield. However, the mechanism by which saline‐alkali stress regulates grain filling in rice is still unclear. In this study, Oryza sativa L. spp. Indica cultivar Chaoyou1000 (C1000) was exposed to post‐anthesis saline‐alkali conditions at 6 days after anthesis, which significantly reduced the grain weight by suppressing the accumulation of starch and non‐structural carbohydrates in grains. Further analysis found that 1‐aminocyclopropane‐1‐carboxylate (ACC), a precursor for ethylene, was increased by saline‐alkali treatment. qRT‐PCR results showed that several key genes involved in ethylene biosynthesis, including the OsACS and OsACO genes, were upregulated in saline‐alkali‐treated grains. In addition, genes involved in the ethylene signalling pathway were also induced by saline‐alkali stress. Exogenous ethylene application reduced grain weight and both starch and NSC contents in grains of C1000, suggesting that saline‐alkali‐induced ethylene has a negative effect on grain filling. Furthermore, the gene expression levels of OsSUS, OsAGPL, OsAGPS, OsSSI and OsSSIIIa, which are key genes in the starch biosynthesis pathway, were downregulated in saline‐alkali‐treated grains. In agreement, assays on these enzymes further revealed that saline‐alkali stress decreased the activities of sucrose synthase (SUS), adenosine diphosphate glucose pyrophosphorylase (AGP) and starch synthase (StS). Together, our results indicated that saline‐alkali stress suppressed the enzyme activities involved in the conversion of sucrose to starch by elevating ethylene production, which led to inhibition of grain filling.

Promoting ethylene production over a wide potential window on Cu crystallites induced and stabilized via current shock and charge delocalization

Electrochemical CO2 reduction (CO2RR) in a product-orientated and energy-efficient manner relies on rational catalyst design guided by mechanistic understandings. In this study, the effect of conducting support on the CO2RR behaviors of semi-conductive metal-organic framework (MOF) — Cu3(HITP)2 are carefully investigated. Compared to the stand-alone MOF, adding Ketjen Black greatly promotes C2H4 production with a stabilized Faradaic efficiency between 60-70% in a wide potential range and prolonged period. Multicrystalline Cu nano-crystallites in the reconstructed MOF are induced and stabilized by the conducting support via current shock and charge delocalization, which is analogous to the mechanism of dendrite prevention through conductive scaffolds in metal ion batteries. Density functional theory calculations elucidate that the contained multi-facets and rich grain boundaries promote C–C coupling while suppressing HER. This study underlines the key role of substrate-catalyst interaction, and the regulation of Cu crystalline states via conditioning the charge transport, in steering the CO2RR pathway.

F-box protein EBF1 and transcription factor ABI5-like regulate banana fruit chilling-induced ripening disorder.

Cold stress adversely affects plant production, both qualitatively and quantitatively. Banana (Musa acuminata) is sensitive to cold stress and suffers chilling injury (CI) when stored under 11°C, causing abnormal fruit softening. However, the mechanism underlying the abnormal fruit softening due to CI remains obscure. This study uncovered the coordinated transcriptional mechanism of ethylene F-box (EBF1) protein and abscisic acid-insensitive 5 (ABI5)-like protein in regulating chilling-induced softening disorders of Fenjiao banana. Cold stress severely inhibited the transcript and protein levels of EBF1, ABI5-like, and fruit softening-related genes. The ABI5-like protein bound to the promoters of key starch and cell wall degradation-related genes such as β-amylase 8 (BAM8), pectate lyase 8 (PL8), and β-D-xylosidase23-like (XYL23-like) and activated their activities. EBF1 physically interacted with ABI5-like and enhanced the transcriptional activity of the key starch and cell wall degradation-related genes but did not ubiquitinate or degrade ABI5-like protein. This promoted fruit ripening and ameliorated fruit CI in a manner similar to the effect of exogenous abscisic acid treatment. The ectopic and transient overexpression of EBF1 and ABI5-like genes in tomato (Solanum lycopersicum) and Fenjiao banana accelerated fruit ripening and softening by promoting ethylene production, starch and cell wall degradation, and decreasing fruit firmness. EBF1 interacted with EIL4 but did not ubiquitinate or degrade EIL4, which is inconsistent with the typical role of EBF1/2 in Arabidopsis (Arabidopsis thaliana). These results collectively highlight that the interaction of EBF1 and ABI5-like controls starch and cell wall metabolism in banana, which is strongly inhibited by chilling stress, leading to fruit softening and ripening disorder.

Distinct Functions of Ethylene and ACC in the Basal Land Plant Marchantia polymorpha

Ethylene is a gaseous phytohormone involved in various physiological processes, including fruit ripening, senescence, root hair development and stress responses. Recent genomics studies have suggested that most homologous genes of ethylene biosynthesis and signaling are conserved from algae to angiosperms, whereas the function and biosynthesis of ethylene remain unknown in basal plants. Here, we examined the physiological effects of ethylene, an ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) and an inhibitor of ethylene perception, silver thiosulfate (STS), in a basal land plant, Marchantia polymorpha. M. polymorpha plants biosynthesized ethylene, and treatment with high concentrations of ACC slightly promoted ethylene production. ACC remarkably suppressed the growth of thalli (vegetative organs) and rhizoids (root-hair-like cells), whereas exogenous ethylene slightly promoted thallus growth. STS suppressed thallus growth and induced ectopic rhizoid formation on the dorsal surface of thalli. Thus, ACC and ethylene have different effects on the vegetative growth of M. polymorpha. We generated single and double mutants of ACC synthase-like (ACSL) genes, MpACSL1 and MpACSL2. The mutants did not show obvious defects in thallus growth, ACC content and ethylene production, indicating that MpACSL genes are not essential for the vegetative growth and biosynthesis of ACC and ethylene. Gene expression analysis suggested the involvement of MpACSL1 and MpACSL2 in stress responses. Collectively, our results imply ethylene-independent function of ACC and the absence of ACC-mediated ethylene biosynthesis in M. polymorpha.

Ethylene increases the cold tolerance of apple via the MdERF1B-MdCIbHLH1 regulatory module.

Cold stress has always been a major abiotic factor affecting the yield and quality of temperate fruit crops. Ethylene plays a critical regulatory role in the cold stress response, but the underlying molecular mechanisms remain elusive. Here, we revealed that ethylene positively modulates apple responses to cold stress. Treatment with 1-aminocyclopropane-1-carboxylate (an ethylene precursor) and aminoethoxyvinylglycine (an ethylene biosynthesis inhibitor) respectively increased and decreased the cold tolerance of apple seedlings. Consistent with the positive effects of ethylene on cold stress responses, a low-temperature treatment rapidly induced ethylene release and the expression of MdERF1B, which encodes an ethylene signaling activator, in apple seedlings. Overexpression of MdERF1B significantly increased the cold tolerance of apple plant materials (seedlings and calli) and Arabidopsis thaliana seedlings. A quantitative real-time PCR analysis indicated that MdERF1B upregulates the expression of the cold-responsive gene MdCBF1 in apple seedlings. Moreover, MdCIbHLH1, which functions upstream of CBF-dependent pathways, enhanced the binding of MdERF1B to target gene promoters as well as the consequent transcriptional activation. The stability of MdERF1B-MdCIbHLH1 was affected by cold stress and ethylene. Furthermore, MdERF1B interacted with the promoters of two genes critical for ethylene biosynthesis, MdACO1 and MdERF3. The resulting upregulated expression of these genes promoted ethylene production. However, the downregulated MdCIbHLH1 expression in MdERF1B-overexpressing apple calli significantly inhibited ethylene production. These findings imply that MdERF1B-MdCIbHLH1 is a potential regulatory module that integrates the cold and ethylene signaling pathways in apple.

The mechanism for brassinosteroids suppressing climacteric fruit ripening.

The plant hormone ethylene is important for the ripening of climacteric fruit, such as pear (Pyrus ussuriensis), and the brassinosteroid (BR) class of phytohormones affects ethylene biosynthesis during ripening via an unknown molecular mechanism. Here, we observed that exogenous BR treatment suppressed ethylene production and delayed fruit ripening, whereas treatment with a BR biosynthesis inhibitor promoted ethylene production and accelerated fruit ripening in pear, suggesting BR is a ripening suppressor. The expression of the transcription factor BRASSINAZOLE-RESISTANT 1PuBZR1 was enhanced by BR treatment during pear fruit ripening. PuBZR1 interacted with PuACO1, which converts 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, and suppressed its activity. BR-activated PuBZR1 bound to the promoters of PuACO1 and of PuACS1a, which encodes ACC synthase, and directly suppressed their transcription. Moreover, PuBZR1 suppressed the expression of transcription factor PuERF2 by binding its promoter, and PuERF2 bound to the promoters of PuACO1 and PuACS1a. We concluded that PuBZR1 indirectly suppresses the transcription of PuACO1 and PuACS1a through its regulation of PuERF2. Ethylene production and expression profiles of corresponding apple (Malus domestica) homologs showed similar changes following epibrassinolide treatment. Together, these results suggest that BR-activated BZR1 suppresses ACO1 activity and the expression of ACO1 and ACS1, thereby reducing ethylene production and suppressing fruit ripening. This likely represents a conserved mechanism by which BR suppresses ethylene biosynthesis during climacteric fruit ripening.

ERF4 affects fruit firmness through TPL4 by reducing ethylene production.

The firmness of fleshy fruit crops has a significant effect on their quality, consumer preference, shelf life and transportability. In a combined quantitative trait locus and genome-wide association studies study of apple fruit texture, we identified a mutation (C-G) in the ethylene response factor-associated amphiphilic repression (EAR) motif in the coding region of the apple ETHYLENE RESPONSE FACTOR4 (ERF4) gene. Chromatin immunoprecipitation sequencing showed that ERF4 binds to the promoter of ERF3, which is involved in regulation of ethylene biosynthesis. The EAR mutation in ERF4 results in reduced repression of ERF3 expression, which is turn promotes ethylene production and loss of fruit firmness. ERF4 acts as a transcriptional repressor whose activity is modulated by a TOPLESS co-repressor 4 (TPL4)-binding EAR repression motif. Biolayer interferometry analysis showed that the mutation in the EAR motif causes a reduction in the interaction with TPL4. Suppression of ERF4 or TPL4 promoted fruit ripening and ethylene production. Taken together, our results provide insights into how ERF4 allelic variation underlies an important fruit quality trait.

Auxin-activated MdARF5 induces the expression of ethylene biosynthetic genes to initiate apple fruit ripening.

Summary The gaseous plant hormone ethylene induces the ripening of climacteric fruit, including apple (Malus domestica). Another phytohormone, auxin, is known to promote ethylene production in many horticultural crops, but the regulatory mechanism remains unclear.Here, we found that auxin application induces ethylene production in apple fruit before the stage of commercial harvest, when they are not otherwise capable of ripening naturally.The expression of MdARF5, a member of the auxin response factor transcription factor (TF) family involved in the auxin signaling pathway, was enhanced by treatment with the synthetic auxin naphthaleneacetic acid (NAA). Further studies revealed that MdARF5 binds to the promoter of MdERF2, encoding a TF in the ethylene signaling pathway, as well as the promoters of two 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) genes (MdACS3a and MdACS1) and an ACC oxidase (ACO) gene, MdACO1, all of which encode key steps in ethylene biosynthesis, thereby inducing their expression. We also observed that auxin‐induced ethylene production was dependent on the methylation of the MdACS3a promoter.Our findings reveal that auxin induces ethylene biosynthesis in apple fruit through activation of MdARF5 expression.

Coronatine inhibits mesocotyl elongation by promoting ethylene production in etiolated maize seedlings

Maize (Zea mays L.) is one of the most important cereal crops in the world. In order to survive, plants must regulate their growth in response to multiple developmental and environmental cues, including modulating lodging stress. Coronatine is a chlorosis-inducing non-host-specific phytotoxin produced by several members of the Pseudomonas syringe group of pathovars, which can lead to leaf chlorosis, anthocyanin production, and growth inhibition. In this study, we investigated the physiological mechanism for coronatine during maize mesocotyl growth and development. Using ethephon as a positive control, we found that coronatine inhibited the elongation of mesocotyls in maize B73 etiolated seedlings which was related to ethylene production. Both coronatine and ethephon increased mesocotyls coarsening by increasing the cell diameter and shortened it by inhibiting cell elongation. Coronatine also thickened cell walls in longitudinal and transverse sections by increasing the expression of the cellulose lignin synthesis gene ZmEXT. To further verify the correlation between coronatine and ethephon during mesocotyl growth, we detected the release of endogenous ethylene and the expression of ZmACOs and ZmACSs. We found that coronatine increased the ethylene production while inhibiting auxin synthesis, thereby inhibiting mesocotyl growth.

Overexpression of a basic helix-loop-helix transcription factor gene, SlbHLH22, promotes early flowering and accelerates fruit ripening in tomato (Solanum lycopersicum L.).

The overexpression of SlbHLH22 functioned in controlling flowering time, accelerated fruit ripening, and produced more ethylene-producing phenotypes in tomato. Flowering and fruit ripening are two complex transition processes regulated by various internal and external factors that ultimately lead to fruit maturation and final seed dispersal. The basic helix-loop-helix (bHLH) transcription factor is the largest TF gene family in plants that controls various biological and developmental aspects, but the actual roles of these genes have not been fully studied. Here, we performed a functional characterization of the bHLH gene SlbHLH22 in tomato. SlbHLH22 was fully expressed in tomato flowers, while a moderate expression level was also observed in fruits at different developmental stages. Overexpression of the SlbHLH22 gene revealed that it is highly involved in controlling flowering time, through the activation of the SlSFT or SlLFY genes, and promoting fruit ripening and improved carotenoid accumulation. The expression patterns of carotenoid-related genes (SlPYS1) were also upregulated in transgenic tomato fruits. In transgenic tomato fruit, we observed clear changes in colour from green to orange with enhanced expression of the SlbHLH22 gene. SlbHLH22 was upregulated under exogenous ACC, IAA, ABA, and ethephon. Overexpression of SlbHLH22 also promotes ethylene production. Moreover, ethylene biosynthesis and perception genes (SlACO3, SlACS1, SlACS2, SlACS4, SlACS1a, SlEIN1, SlEIN2, SlEIN3, SlEIN4, SlETR2, SlETR3, SlSAM3, and SlSAMS) were upregulated. Ripening-related genes (SlAP2a, SlCNR, SlNOR, SlMYB, and SlTAG) were consistent in their expression pattern in transgenic plants. Finally, our study provides evidence that tomato bHLH genes play an important role in flowering, fruit ripening, and development.