Ethylene Biosynthesis Inhibitor Research Articles

ХРАНЕНИЕ ТОМАТОВ – ТРАДИЦИОННЫЕ И ПЕРСПЕКТИВНЫЕ ТЕХНОЛОГИИ

As known, tomatoes contain a fairly large amount of biologically valuable substances in their composition. Consumers prefer tomatoes in fresh form. However, being a climacteric crop, tomatoes differ during storage and maturation by a high rate of respiration and evaporation of moisture, which leads to a decrease in valuable nutrients, deterioration in quality, over-ripening and rapid aging, which as a result reduces the marketable appearance of products. Traditional methods of processing tomatoes before storage are not always effective enough to maintain the quality of tomato fruits at the proper level, since it is not always possible to store tomatoes at the recommended low temperature, the necessary relative humidity, etc. In order to increase the storage time of tomatoes while maintaining their quality and safety, it is necessary to search for new modern methods of fruit processing before storage. In this regard, an overview of existing traditional technologies, as well as modern and promising techniques and methods for preparing fresh tomatoes for storage, contributing to the reduction of quantitative losses, preserving qualitative characteristics, is carried out. The most promising methods of preliminary preparation of tomatoes for storage, providing a high level of physical-chemical, organoleptic and microbiological indicators that ensure the safety of stored products are: treatment with ethylene biosynthesis inhibitors and ethylene absorbers, ozonation, modified gas atmosphere, electric field and ultrasound treatment, the use of biological products, the use of active packaging, antimicrobial film-forming coatings, etc. The article describes the work of both domestic and foreign researchers. Keywords: FRESH TOMATOES, PROCESSING, STORAGE TECHNOLOGY, QUALITY

Biosynthesis of Strained Amino Acids by a PLP‐Dependent Enzyme through Cryptic Halogenation

Amino acids (AAs) are modular building blocks which nature uses to synthesize both macromolecules, such as proteins, and small molecule natural products, such as alkaloids and non‐ribosomal peptides. While the 20 main proteinogenic AAs display relatively limited side chain diversity, a wide range of non‐canonical amino acids (ncAAs) exist that are not used by the ribosome for protein synthesis, but contain a broad array of structural features and functional groups. In this communication, we report the discovery of the biosynthetic pathway for a new ncAA, pazamine, which contains a cyclopropane ring formed in two steps. In the first step, a chlorine is added onto the C4 position of lysine by a radical halogenase, PazA. The cyclopropane ring is then formed in the next step by a pyridoxal‐5’‐phosphate‐dependent enzyme, PazB, via an SN2‐like attack at C4 to eliminate chloride. Genetic studies of this pathway in the native host, Pseudomonas azotoformans, show that pazamine potentially inhibits ethylene biosynthesis in growing plants based on alterations in the root phenotype of Arabidopsis thaliana seedlings. We further show that PazB can be utilized to make an alternative cyclobutane‐containing AA. These discoveries may lead to advances in biocatalytic production of specialty chemicals and agricultural biotechnology.

Biosynthesis of Strained Amino Acids by a PLP-Dependent Enzyme through Cryptic Halogenation.

Amino acids (AAs) are modular building blocks which nature uses to synthesize both macromolecules, such as proteins, and small molecule natural products, such as alkaloids and non-ribosomal peptides. While the 20 main proteinogenic AAs display relatively limited side chain diversity, a wide range of non-canonical amino acids (ncAAs) exist that are not used by the ribosome for protein synthesis, but contain a broad array of structural features and functional groups. In this communication, we report the discovery of the biosynthetic pathway for a new ncAA, pazamine, which contains a cyclopropane ring formed in two steps. In the first step, a chlorine is added onto the C4 position of lysine by a radical halogenase, PazA. The cyclopropane ring is then formed in the next step by a pyridoxal-5'-phosphate-dependent enzyme, PazB, via an SN2-like attack at C4 to eliminate chloride. Genetic studies of this pathway in the native host, Pseudomonas azotoformans, show that pazamine potentially inhibits ethylene biosynthesis in growing plants based on alterations in the root phenotype of Arabidopsis thaliana seedlings. We further show that PazB can be utilized to make an alternative cyclobutane-containing AA. These discoveries may lead to advances in biocatalytic production of specialty chemicals and agricultural biotechnology.

Ambient temperature regulates root circumnutation in rice through the ethylene pathway: transcriptome analysis reveals key genes involved.

Plant roots are constantly prepared to adjust their growth trajectories to avoid unfavorable environments, and their ability to reorient is particularly crucial for survival. Under laboratory conditions, this continuous reorientation of the root tip is manifested as coiling or waving, which we refer to as root circumnutation. However, the effect of ambient temperature (AT) on root circumnutation remains unexplored. In this study, rice seedlings were employed to assess the impact of varying ATs on root circumnutation. The role of ethylene in mediating root circumnutation under elevated AT was examined using the ethylene biosynthesis inhibitor aminooxyacetic acid (AOA) and the ethylene perception antagonist silver thiosulfate (STS). Furthermore, transcriptome sequencing, weighted gene co-expression network analysis, and real-time quantitative PCR were utilized to analyze gene expressions in rice root tips under four distinct treatments: 25°C, 35°C, 35°C+STS, and 35°C+AOA. As a result, genes associated with ethylene synthesis and signaling (OsACOs and OsERFs), auxin synthesis and transport (OsYUCCA6, OsABCB15, and OsNPFs), cell elongation (OsEXPAs, OsXTHs, OsEGL1, and OsEXORDIUMs), as well as the inhibition of root curling (OsRMC) were identified. Notably, the expression levels of these genes increased with rising temperatures above 25°C. This study is the first to demonstrate that elevated AT can induce root circumnutation in rice via the ethylene pathway and proposes a potential molecular model through the identification of key genes. These findings offer valuable insights into the growth regulation mechanism of plant roots under elevated AT conditions.

Elevated CO2-conferred sodium homeostasis is linked to abscisic acid-mediated stomatal closure and signalling pathway in tomato plants

Soil salinity hampers plant performance. Elevated atmospheric CO2 (e[CO2]) could alleviate the detrimental effect of salinity on plants but whether abscisic acid (ABA) is involved in this process is unclear. To address this issue, three tomato (Solanum lycopersicum) genotypes with varying endogenous ABA concentrations (wild-type AC, ABA-deficient mutant flacca and ABA-overproduction line SP5) were grown in pots under ambient (400 μmol · mol–1) or elevated (800 μmol · mol–1) CO2 with or without the addition of 100 mmol · L−1sodium chloride (NaCl). The results showed that e[CO2] favored ion homeostasis by decreasing root-to-shoot delivery of Na+, which was mainly attributed to lowered transpiration rate rather than altered xylem-sap Na+ concentration. In AC and SP5, the low transpiration rate of e[CO2]-plants under salinity was accompanied by enhanced endogenous ABA levels, which might play a role in upregulating the abundance of specific transcripts related to Na+ homeostasis (i.e., SALT OVERLY SENSITIVE) under salt stress. In flacca, e[CO2]-induced Na+ homeostasis was abolished, which could be ascribed to the low and unaltered ABA levels, albeit the ethylene biosynthesis was enhanced in flacca under salt stress, indicating an antagonistic relationship between ABA and ethylene. Furthermore, e[CO2] inhibited ethylene biosynthesis under salt stress in all three genotypes. The results enrich our comprehension of the fundamental processes of e[CO2]-conferred salt tolerance in tomato.

Functional mechanismstudy of the allelochemical myrigalone A identifies a group of ultrapotent inhibitors of ethylene biosynthesis in plants.

Allelochemicals represent a class of natural products released by plants as root, leaf, and fruit exudates that interfere with the growth and survival of neighboring plants. Understanding how allelochemicals function to regulate plant responses may provide valuable new approaches to better control plant function. One such allelochemical, Myrigalone A (MyA) produced by Myrica gale, inhibits seed germination and seedling growththrough an unknown mechanism. Here, we investigate MyA using the tractable model Dictyostelium discoideum and reveal that its activity depends on the conserved homologof the plant ethylene synthesis protein1-aminocyclopropane-1-carboxylic acid oxidase (ACO). Furthermore, in silico modeling predicts the direct binding of MyA to ACO within the catalytic pocket. In D. discoideum, ablation of ACO mimics the MyA-dependent developmental delay, which is partially restored by exogenous ethylene, and MyA reduces ethylene production. In Arabidopsis thaliana, MyA treatment delays seed germination, and this effect is rescued by exogenous ethylene. It also mimics the effect of established ACO inhibitors on root and hypocotyl extension, blocks ethylene-dependent root hair production, and reduces ethylene production. Finally, in silico binding analyses identify a range of highly potent ethylene inhibitorsthat block ethylene-dependent response and reduce ethylene production in Arabidopsis. Thus, we demonstrate a molecular mechanism by which the allelochemical MyA reduces ethylene biosynthesis and identify a range of ultrapotent inhibitors of ethylene-regulated responses.

Mangrove species found in contrasting environments show differing phytohormonal responses to variation in soil bulk density

Abstract Background and aims Mangrove species respond to variation in soil bulk density (BD). However, very little is known about the regulatory mechanisms that trigger these responses. Methods Endogenous concentrations of different phytohormones were measured in the roots of two mangrove species (Avicennia marina and Rhizophora stylosa) grown in low and high BD soils. The potential involvement of ethylene in regulating plant growth responses was tested by applying the ethylene biosynthesis inhibitors cobalt chloride (CoCl2) and aminoisobutyric acid (AIB). Results The two mangrove species responded differently to variation in soil BD. High BD decreased root growth of R. stylosa, but not A. marina. Soil BD had no effect on root phytohormone levels in R. stylosa, but loose soils increased 1-aminocyclopropane-1-carboxylic acid whilst decreasing salicylic acid and gibberellin in A. marina. Applying ethylene inhibitors enhanced R. stylosa root growth, while increasing indole-3-acetic acid but decreasing isopentenyl adenine levels. In contrast, AIB inhibited A. marina root growth, while increasing trans-zeatin levels. Ethylene inhibitors affected salicylic acid levels in both species. Conclusion Salicylic acid is central to root growth responses to variation in BD in A. marina. Conversely, the interaction of ethylene and gibberellin drives responses in R. stylosa. Hormonal interactions involving ethylene potentially reflect the adaptations of the two species to differing conditions within the intertidal zone, with A. marina behaving like an aquatic species and R. stylosa behaving like a terrestrial species.

The impact of growing season on the ethylene biosynthesis and signaling pathways of a heat tolerant tomato during off-vine postharvest ripening

Ethylene initiates and mediates fruit ripening throughout a cascade of signal transductions from ethylene receptors (ETRs) to ethylene response factors (ERFs). High temperatures impair fruit ripening by suppressing ethylene biosynthesis and parts of physiological and biochemical processes. This study made use of the ethylene inhibitor (1-MCP) and exogenous ethylene to investigate the ethylene biosynthesis and signaling pathways of a heat tolerant tomato cultivar, cv. ‘Savior’, during off-vine postharvest ripening during two distinct growing seasons. Mature green ’Savior‘ tomatoes grown in winter (mild temperature) and summer (high temperature) were harvested at and treated with 1-MCP or exogenous ethylene. During off-vine ripening, summer fruit showed a different ethylene biosynthesis profile compared to winter fruit. The application of exogenous ethylene did not accelerate fruit ripening of the heat tolerant cultivar. 1-MCP suppressed ethylene production for a long time, and delayed fruit ripening of winter tomato, while for summer fruit, a limited effect of 1-MCP on inhibiting ethylene biosynthesis and delaying ripening was observed despite the strong suppression of ACC oxidase (ACO) activity. Our work also showed that a 1-MCP treatment reduced gene expression of several ethylene receptors (ETR) but did not have a strong effect on constitutive triple response (CTR), except CTR1, and ethylene-insensitive protein 2 (EIN2). Overall, our results indicate that i) ethylene biosynthesis is differentially regulated in winter as compared to summer fruit by ethylene signaling, ii) a high cultivation temperature impacts ethylene biosynthesis and ethylene sensitivity during fruit ripening despite the fact that this is a heat tolerant cultivar, iii) the expression of most ETRs and CTRs, and especially EIN2 did not respond to the 1-MCP or ethylene treatment.

The Potential of Essential Oils from Active Packaging to Reduce Ethylene Biosynthesis in Plant Products. Part 2: Fruits (Blueberries and Blackberries).

Plant essential oils (EOs) have an important ability to inhibit ethylene biosynthesis. Nevertheless, the effects of EOs on the key components of ethylene biosynthesis (l-aminocyclopropane-1-carboxylic (ACC) oxidase activity, ACC synthase activity, and ACC content) have not yet been thoroughly studied. Accordingly, this study focused on the effects of emitted EOs from active packaging (EO doses from 100 to 1000 mg m-2) on the key components of ethylene biosynthesis of blueberries and blackberries under several storage temperatures. Anise EO and lemon EO active packaging induced the greatest inhibitory effects (60-76%) on the ethylene production of blueberries and blackberries, respectively, even at high storage temperatures (22 °C). In terms of EO doses, active packaging with 1000 mg m-2 of anise EO or lemon EO led to the highest reduction of ethylene production, respectively. At 22 °C, the investigated EO active packing reduced the activities of ACC synthase and ACC oxidase up to 50%. In order to minimise ethylene biosynthesis in blueberries and blackberries when they are stored even under improper temperature scenarios at high temperatures, this EO active packaging is a natural and efficient technological solution.

Brassinosteroid modulates ethylene synthesis and antioxidant metabolism to protect rice (Oryza sativa) against heat stress-induced inhibition of source‒sink capacity and photosynthetic and growth attributes

This study presents an exploration of the efficacy of brassinosteroids (BRs) and ethylene in mediating heat stress tolerance in rice (Oryza sativa). Heat is one of the major abiotic factors that prominently deteriorates rice production by influencing photosynthetic efficiency, source‒sink capacity, and growth traits. The application of BR (0.5 mM) and ethylene (200 μl l−1) either individually and/or in combination was found to alleviate heat stress-induced toxicity by significantly improving photosynthesis, source‒sink capacity and defense systems; additionally, it reduced the levels of oxidative stress markers and ethylene formation. The study revealed the positive influence of BR in promoting plant growth responses under heat stress through its interplay with ethylene biosynthesis and enhanced plant defense systems. Interestingly, treatment with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) substantiated that BR application to heat-stressed rice plants enhanced ethylene-dependent pathways to counteract the underlying adversities. Thus, BR action was found to be mediated by ethylene to promote heat tolerance in rice. The present study sheds light on the potential tolerance mechanisms which can ensure rice sustainability under heat stress conditions.

Methyl jasmonate influences ethylene formation, defense systems, nutrient homeostasis and carbohydrate metabolism to alleviate arsenic-induced stress in rice (Oryza sativa)

The plant growth regulator, jasmonic acid (JA) has emerged as important molecule and involved in key processes of plants. In this study, we investigated the role of methyl jasmonate (MeJA) in achieving tolerance mechanisms against arsenic (As) stress in rice (Oryza sativa). Arsenic toxicity is a major global concern that significantly deteriorate rice production. The application of MeJA (20 μM) and ethylene (150 μL L−1) both individually and/or in combination were found significant in protecting against As-induced toxicity in rice, and significantly improved defense systems. The study shown that the positive influence of MeJA in promoting carbohydrate metabolism, photosynthesis and growth under As stress were the result of its interplay with ethylene biosynthesis and reduced oxidative stress-mediated cellular injuries and cell deaths. Interestingly, the use of JA biosynthesis inhibitor, neomycin (Neo) and ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG) overturned the effects of MeJA and ethylene on plant growth under As stress. From the pooled data, it may also be concluded that Neo treatment to MeJA- treated rice plants restricted JA-mediated responses, implying that application of MeJA modulated ethylene- dependent pathways in response to As stress. Thus, the action of MeJA in As tolerance is found to be mediated by ethylene. The study will shed light on the mechanisms that could be used to ensure the sustainability of rice plants under As stress.

Multi-omic analysis of the extension of broccoli quality during storage by folic acid

IntroductionFolic acid (FA) is a critical metabolite in all living organisms and an important nutritional component of broccoli. Few studies have been conducted on the impact of an exogenous application of FA on the postharvest physiology of fruits and vegetables during storage. In this regard, the mechanism by which an exogenous application of FA extends the postharvest quality of broccoli is unclear. ObjectiveThis study utilized a multicomponent analysis to investigate how an exogenous application of FA effects the postharvest quality of broccoli. MethodsBroccoli was soaked in 5 mg/L FA for 10 min and the effect of the treatment on the appearance and nutritional quality of broccoli was evaluated. These data were combined with transcriptomic, metabolomic, and DNA methylation data to provide insight into the potential mechanism by which FA delays senescence. ResultsThe FA treatment inhibited the yellowing of broccoli during storage. CHH methylation was identified as the main type of methylation that occurs in broccoli and the FA treatment was found to inhibit DNA methylation, promote the accumulation of endogenous FA and chlorophyl, and inhibit ethylene biosynthesis in stored broccoli. The FA treatment also prevented the formation of off-odors by inhibiting the degradation of glucosinolate. ConclusionsFA treatment inhibited the loss of nutrients during the storage of broccoli, delayed its yellowing, and inhibited the generation of off-odors. Our study provides deeper insight into the mechanism by which the postharvest application of FA delays postharvest senescence in broccoli and provides the foundation for further studies of postharvest metabolism in broccoli.

The local and systemic accumulation of ethylene determines the rapid defence responses induced by flg22 in tomato (Solanum lycopersicum L.)

Plant defence responses induced by the bacterial elicitor flg22 are highly dependent on phytohormones, including gaseous ethylene (ET). While the regulatory role of ET in local defence responses to flg22 exposure has been demonstrated, its contribution to the induction of systemic responses is not clearly understood. For this consideration, we examined the effects of different ET modulators on the flg22-induced local and systemic defence progression. In our experiments, ET biosynthesis inhibitor aminoethoxyvinyl glycine (AVG) or ET receptor blocker silver thiosulphate (STS) were applied 1 h before flg22 treatments and 1 h later the rapid local and systemic responses were detected in the leaves of intact tomato plants (Solanum lycopersicum L.). Based on our results, AVG not only diminished the flg22-induced ET accumulation locally, but also in the younger leaves confirming the role of ET in the whole-plant expanding defence progression. This increase in ET emission was accompanied by increased local expression of SlACO1, which was reduced by AVG and STS. Local ET biosynthesis upon flg22 treatment was shown to positively regulate local and systemic superoxide (O2.-) and hydrogen peroxide (H2O2) production, which in turn could contribute to ET accumulation in younger leaves. Confirming the role of ET in flg22-induced rapid defence responses, application of AVG reduced local and systemic ET, O2.- and H2O2 production, whereas STS reduced it primarily in the younger leaves. Interestingly, in addition to flg22, AVG and STS induced stomatal closure alone at whole-plant level, however in the case of combined treatments together with flg22 both ET modulators reduced the rate of stomatal closure in the older- and younger leaves as well. These results demonstrate that both local and systemic ET production in sufficient amounts and active ET signalling are essential for the development of flg22-induced rapid local and systemic defence responses.

Peronophythora litchii RXLR effector P. litchii avirulence homolog 202 destabilizes a host ethylene biosynthesis enzyme.

Oomycete pathogens can secrete hundreds of effectors into plant cells to interfere with the plant immune system during infection. Here, we identified a Arg-X-Leu-Arg (RXLR) effector protein from the most destructive pathogen of litchi (Litchi chinensis Sonn.), Peronophythora litchii, and named it P. litchii avirulence homolog 202 (PlAvh202). PlAvh202 could suppress cell death triggered by infestin 1 or avirulence protein 3a/resistance protein 3a in Nicotiana benthamiana and was essential for P. litchii virulence. In addition, PlAvh202 suppressed plant immune responses and promoted the susceptibility of N. benthamiana to Phytophthora capsici. Further research revealed that PlAvh202 could suppress ethylene (ET) production by targeting and destabilizing plant S-adenosyl-L-methionine synthetase (SAMS), a key enzyme in the ET biosynthesis pathway, in a 26S proteasome-dependent manner without affecting its expression. Transient expression of LcSAMS3 induced ET production and enhanced plant resistance, whereas inhibition of ET biosynthesis promoted P. litchii infection, supporting that litchi SAMS (LcSAMS) and ET positively regulate litchi immunity toward P. litchii. Overall, these findings highlight that SAMS can be targeted by the oomycete RXLR effector to manipulate ET-mediated plant immunity.

LED white light-activated transcription factor MdHY5 inhibits ethylene biosynthesis during apple fruit ripening

Ethylene is one of the most important plant hormones involved in the climacteric fruit ripening process. Apple is a climacteric fruit, and its ripening process is regulated by ethylene. The effect of light-emitting diode (LED) light on plant growth and development has been extensively investigated; however, it remains unclear how LED light affects apple fruit ripening. Herein, we observed that the ripening of apple fruit treated with eight kinds of LED light was significantly inhibited compared with that of the dark control, with inhibition by white light being the most significant. Furthermore, the optimal light intensity for the inhibition of ethylene production was 20 μmol·m−2s−1, with an optimal light duration of 12 h per day. LED white light treatment enhanced the expression of two ELONGATED HYPOCOTYL 5 (HY5) genes, MdHY5L and MdHY5S, which encode transcription factors involved in the light signaling pathway. These two HY5s inhibited the transcription of MdACS1, a crucial rate-limiting enzyme in the ethylene synthesis pathway, by directly binding to its promoter. Collectively, these findings imply that LED white light induces the expression of MdHY5L and MdHY5S and delays the expression of the ethylene synthesis-related gene MdACS1 to prevent fruit ripening. This study preliminarily elucidates the molecular mechanism underlying LED white light-induced inhibition of ethylene synthesis in apple fruit, providing an important theoretical basis for studying how to improve the storage ability and prolong the shelf life of apple fruit.

Ethylene Inhibition Reduces De Novo Shoot Organogenesis and Subsequent Plant Development from Leaf Explants of Solanum betaceum Cav.

In de novo shoot organogenesis (DNSO) plant cells develop into new shoots, without the need of an existing meristem. Generally, this process is triggered by wounding and specific growth regulators, such as auxins and cytokinins. Despite the potential significance of the plant hormone ethylene in DNSO, its effect in regeneration processes of woody species has not been thoroughly investigated. To address this gap, Solanum betaceum Cav. was used as an experimental model to explore the role of this hormone on DNSO and potentially extend the findings to other woody species. In this work it was shown that ethylene positively regulates DNSO from tamarillo leaf explants. Ethylene precursors ACC and ethephon stimulated shoot regeneration by increasing the number of buds and shoots regenerated. In contrast, the inhibition of ethylene biosynthesis or perception by AVG and AgNO3 decreased shoot regeneration. Organogenic callus induced in the presence of ethylene precursors showed an upregulated expression of the auxin efflux carrier gene PIN1, suggesting that ethylene may enhance shoot regeneration by affecting auxin distribution prior to shoot development. Additionally, it was found that the de novo shoot meristems induced in explants in which ethylene biosynthesis and perception was suppressed were unable to further develop into elongated shoots. Overall, these results imply that altering ethylene levels and perception could enhance shoot regeneration efficiency in tamarillo. Moreover, we offer insights into the possible molecular mechanisms involved in ethylene-induced shoot regeneration.

Enhancement of Postharvest Life of Fruits by Application of Salicylic Acid

Salicylic acid (SA), an endogenous plant growth regulator, has been found to produce a wide range of metabolic and physiological responses in plants thereby affecting their growth and development. SA as a natural and safe phenolic compound, which exhibits a high potential in controlling postharvest losses of fruit crops. In this review, various intrinsic biosynthetic pathways and effects of exogenous salicylic acid on respiration, antioxidant systems, ethylene biosynthesis action, oxidative stress, nutritional quality, firmness, disease resistance and postharvest decay have also been discussed. Salicylates (derivatives of salicylic acid) delay the ripening of fruits, probably through inhibition of ethylene biosynthesis or action, and maintain postharvest quality.

A novel NAC transcription factor, PpNAP6, is involved in peach ripening by activating ethylene synthesis

Peach (Prunus persica) is a typical climacteric fruit, having an obvious peak of ethylene release during ripening. Transcriptional regulators play key roles in fruit ripening. NAP (NAC-like, activated by AP3/P1) protein is a subfamily of the NAC (NAM, ATAF1/2 and CUC2) transcription factor (TF) family. Here, we discovered the function of peach NAP subfamily NAC TF, PpNAP6, homologous to the tomato ripening-related TF NOR. In the pulp of ‘Zaofengwang’ peach, PpNAP6 is highly expressed, and its transcript level decreased gradually throughout the whole development period, however, it is up-regulated at onset of peach ripening. Transient transformation experiments showed that PpNAP6 over-expression in peach fruit increased ethylene release and accelerated fruit ripening, while PpNAP6 down-expression inhibited ethylene biosynthesis. Dual-luciferase reporter assay (DLR) and electrophoretic mobility shift assay (EMSA) proved that PpNAP6 can directly bind to the promoters of key ethylene biosynthesis genes PpACS1 and PpACO1, and activate their transcription. Moreover, PpNAP6 was heterologously overexpressed in tomato nor mutant, and the transgenic lines showed the overexpression of PpNAP6 could partially recover its ripening-inhibited phenotype. Interestingly, PpNAP6 activates ethylene biosynthesis during peach ripening, whereas its transcription was inhibited treated with ethephon and enhanced with 1-MCP treatment. In summary, our work revealed that PpNAP6 regulates peach fruit ripening through ethylene biosynthesis, and may be involved in the fine regulation of ethylene via a feedback mechanism.

Nitric oxide in co-ordination with nitrogen reverses cadmium-inhibited photosynthetic activity by interacting with ethylene synthesis, strengthening the antioxidant system, and nitrogen and sulfur assimilation in mustard (Brassica juncea L.)

Nitric oxide (NO) is a gaseous signaling molecule with known prominent roles in plant development and abiotic stress acclimation. This study reports that NO plus nitrogen (N) conspicuously alleviated cadmium (Cd)-inhibited photosynthetic activity by interacting with ethylene synthesis, and modifying the mechanisms of antioxidant enzymes, N and sulfur (S) assimilation in mustard (Brassica juncea L.) cv. Giriraj plants. The application of 100 µM sodium nitroprusside (SNP; NO donor) and 200 mg N kg−1 soil (as ammonium nitrate) to 200 mg Cd kg−1 soil-grown plants reduced oxidative stress (superoxide radical, hydrogen peroxide, and thiobarbituric acid reactive species content) and cell death through enhanced synthesis of metal chelators (non-protein thiols and phytochelatins) and limited Cd translocation. The reduced cellular ROS was also related to NO and N-mediated enhancement of S and N-assimilation, and antioxidants. The NO and N-mediated higher expression of psbA and psbB genes of D1 protein of PSII resulted into higher photosynthetic performance even under higher Cd regimes. Further, NO and N in the presence of aminoethoxyvinylglycine (AVG, ethylene biosynthesis inhibitor) under Cd stress showed reduced growth and photosynthetic attributes, with greater oxidative stress, substantiating ethylene involvement in NO and N-mediated reversal of Cd-inhibited photosynthesis. The principal component analysis showed a positive correlation between the treatment SNP + N + Cd and NO production, antioxidant enzymes, glutathione and metal chelators which resulted in higher N and S-assimilation, and better growth and photosynthetic capacity under Cd stress. The results indicate that NO-mediated alleviation of Cd toxicity and protection of photosynthetic activity were more conspicuous with N availability through the coordination with ethylene synthesis. The outcome of the study may be utilized in maintaining and managing hostile soils polluted with potentially toxic metals like Cd.

Phytohormone ethylene mediates oligogalacturonic acid-induced growth inhibition in tomato etiolated seedlings

Plant growth and immunity are tightly interconnected. Oligogalacturonic acids (OGs) are pectic fragments and have been well investigated in plant immunity as a damage-associated molecular pattern. However, little is known regarding how OGs affect plant growth. Here, we reveal that OGs inhibit the growth of intact etiolated seedling by using the horticultural crop tomato as a model. This inhibitory effect is partially suppressed by the action of ethylene biosynthesis inhibitors, or the gene silencing of SlACS2, an essential rate-limiting enzyme for ethylene biosynthesis, suggesting that SlACS2-mediated ethylene production promotes OG-induced growth inhibition. Furthermore, OGs treatment elevates the SlACS2 protein phosphorylation, and its decrease by the kinase inhibitor K252a partially rescue OG-induced growth inhibition, indicating that SlACS2 phosphorylation involves in OG-induced growth inhibition. Moreover, the mitogen-activated protein kinase SlMPK3 could be activated by OGs treatment and can directly phosphorylate SlACS2 in vitro, and the bimolecular fluorescence complementation combining with the yeast two-hybrid assay shows that SlMPK3 interacts with SlACS2, indicating that SlMPK3 may participate in modulating the OG-induced SlACS2 phosphorylation and growth inhibition. Our results reveal a regulatory mechanism at both the transcriptional and post-transcriptional levels by which OGs inhibit the growth of intact plant seedlings.