Ethylene Synthesis In Plants Research Articles

Insights into ACO genes across Rosaceae: evolution, expression, and regulatory networks in fruit development.

ACO (1-aminocyclopropane-1-carboxylic acid) serves as a pivotal enzyme within the plant ethylene synthesis pathway, exerting influence over critical facets of plant biology such as flowering, fruit ripening, and seed development. This study aims to identify ACO genes from representative Rosaceae genomes, reconstruct their phylogenetic relationships by integrating synteny information, and investigate their expression patterns and networks during fruit development. we utilize a specialized Hidden Markov Model (HMM), crafted on the sequence attributes of ACO gene-encoded proteins, to systematically identify and analyze ACO gene family members across 12 representative species within the Rosaceae botanical family. Through transcriptome analysis, we delineate the expression patterns of ACO genes in six distinct Rosaceae fruits. Our investigation reveals the presence of 62 ACO genes distributed among the surveyed Rosaceae species, characterized by hydrophilic proteins predominantly expressed within the cytoplasm. Phylogenetic analysis categorizes these ACO genes into three discernible classes, namely Class I, Class II, and Class III. Further scrutiny via collinearity assessment indicates a lack of collinearity relationships among these classes, highlighting variations in conserved motifs and promoter types within each class. Transcriptome analysis unveils significant disparities in both expression levels and trends of ACO genes in fruits exhibiting respiratory bursts compared to those that do not. Employing Weighted Gene Co-Expression Network Analysis (WGCNA), we discern that the co-expression correlation of ACO genes within loquat fruit notably differs from that observed in apples. Our findings, derived from Gene Ontology (GO) enrichment results, signify the involvement of ACO genes and their co-expressed counterparts in biological processes linked to terpenoid metabolism and carbohydrate synthesis in loquat. Moreover, our exploration of gene regulatory networks (GRN) highlights the potential pivotal role of the GNAT transcription factor (Ejapchr1G00010380) in governing the overexpression of the ACO gene (Ejapchr10G00001110) within loquat fruits. The constructed HMM of ACO proteins offers a precise and systematic method for identifying plant ACO proteins, facilitating phylogenetic reconstruction. ACO genes from representative Rosaceae fruits exhibit diverse expression and regulative patterns, warranting further function characterizations.

Functional mechanism study 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 growth through an unknown mechanism. Here, we investigate MyA using the tractable model Dictyostelium discoideum and reveal that its activity depends on the conserved homolog of the plant ethylene synthesis protein 1-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 inhibitors that 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.

Targeted plant hologenome editing for plant trait enhancement.

Summary Breeding better crops is a cornerstone of global food security. While efforts in plant genetic improvement show promise, it is increasingly becoming apparent that the plant phenotype should be treated as a function of the holobiont, in which plant and microbial traits are deeply intertwined.Using a minimal holobiont model, we track ethylene production and plant nutritional value in response to alterations in plant ethylene synthesis (KO mutation in ETO1), which induces 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase 5 (ACS5), or microbial degradation of ACC (KO mutation in microbial acdS), preventing the breakdown of the plant ACC pool, the product of ACS5.We demonstrate that similar plant phenotypes can be generated by either specific mutations of plant‐associated microbes or alterations in the plant genome. Specifically, we could equally increase plant nutritional value by either altering the plant ethylene synthesis gene ETO1, or the microbial gene acdS. Both mutations yielded a similar plant phenotype with increased ethylene production and higher shoot micronutrient concentrations. Restoring bacterial AcdS enzyme activity also rescued the plant wild‐t8yp phenotype in an eto1 background.Plant and bacterial genes build an integrated plant–microbe regulatory network amenable to genetic improvement from both the plant and microbial sides.

Thermal risk for common beans due to high temperatures in three counties of Rio Grande do Sul state

Common beans are an important protein source for human diet. Much cultivated in small farms it is considered a subsistence crop, employing little cultivation technology. It presents a high susceptibility to temperatures above 28 °C in reproductive periods, causing abortion of plant parts due to the high temperature triggering the plant ethylene synthesis. The agroclimatic zoning for culture does not emphasis on air temperature, which affects the crop. With these assumptions, the aim of this work was to evaluate the high temperature thermal risk for the bean crop in Cruz Alta, Passo Fundo and São Luiz Gonzaga. From the maximum air temperature data obtained since 1961, we obtained the average frequency of days at which the maximum air temperature was equal or greater than 28 °C in ten-day periods. The bigger thermal risk was found in the third ten-day period of January and in the last ten-day period of December. Passo Fundo showed the better thermal conditions for bean crop. São Luiz Gonzaga, even during periods not indicated for the culture, during winter, still showed happen at least one day of thermal risk.

Measuring light-induced fungal ethylene production enables non-destructive diagnosis of disease occurrence in harvested fruits

Pathogenic fungi cause enormous losses to fruits, and ethylene (ET) is associated with disease development in fruit crops. In this study, ET production of several fungal pathogens was enhanced by light, probably through the free radicals produced by photochemical reactions. Real-time gas analysis showed a sharp increase in ET production when fungal cultures were moved from dark-to-light (DTL). Similarly, light accelerated ET production in the Botrytis cinerea-infected Arabidopsis thaliana plants even when pyrazinamide, the inhibitor for plant ET synthesis, was applied, suggesting that the fungus is responsible for ET production during host invasion. Furthermore, a sharp increase in ET production after DTL transition was observed in B. cinerea-infected tomatoes and grapes, but not in healthy or physically wounded fruits. Taken together, these findings indicate that the DTL-induced ET is specific to the plant materials with fungal infection, and thus represents a candidate marker for non-destructive disease diagnosis of harvested fruits.

Plant Growth Promotion Under Water: Decrease of Waterlogging-Induced ACC and Ethylene Levels by ACC Deaminase-Producing Bacteria.

Some plant growth-promoting bacteria encode for 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which facilitates plant growth and development by lowering the level of stress ethylene under waterlogged conditions. The substrate ACC is the immediate precursor for ethylene synthesis in plants; while bacterial ACC deaminase hydrolyzes this compound into α-ketobutyrate and ammonia to mitigate the adverse effects of the stress caused by ethylene exposure. Here, the structure and function of ACC deaminase, ethylene biosynthesis and waterlogging response, waterlogging and its consequences, role of bacterial ACC deaminase under waterlogged conditions, and effect of this enzyme on terrestrial and riparian plants are discussed.

Surface display of ACC deaminase on endophytic Enterobacteriaceae strains to increase saline resistance of host rice sprouts by regulating plant ethylene synthesis

BackgroundMost endophytic bacteria in consortia, which provide robust and broad metabolic capacity, are attractive for applications in plant metabolic engineering. The aim of this study was to investigate the effects of engineered endophytic bacterial strains on rice sprout ethylene level and growth under saline stress. A protocol was developed to synthesize engineered strains by expressing bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene on cells of endophytic Enterobacter sp. E5 and Kosakonia sp. S1 (denoted as E5P and S1P, respectively).ResultsResults showed that ACC deaminase activities of the engineered strains E5P and S1P were significantly higher than those of the wild strains E5 and S1. About 32–41% deaminase was expressed on the surface of the engineered strains. Compared with the controls without inoculation, inoculation with the wild and engineered strains increased the deaminase activities of sprouts. Inoculation with the engineered strains increased 15–21% more deaminase activities of sprouts than with the wild strains, and reduced the ethylene concentrations of sprouts more significantly than with wild strains (P < 0.05). Inoculation with the wild and engineered strains promoted the growth of sprouts, while the promoting effects were more profound with the engineered strains than with the wild strains. The engineered strains improved saline resistance of sprouts under salt concentrations from 10 to 25 g L−1. The engineered strains promoted longer roots and shoots than the wild strains under the salt stresses, indicating that the ACC deaminases on the endophytic bacterial cells could result in plant-produced ACC degradation and inhibit plant ethylene formation.ConclusionsThe protocols of expressing enzymes on endophytic bacterial cells showed greater potentials than those of plant over-expressed enzymes to increase the efficiency of plant metabolic pathways.

The β-cyanoalanine synthase pathway: beyond cyanide detoxification.

Production of cyanide through biological and environmental processes requires the detoxification of this metabolic poison. In the 1960s, discovery of the β-cyanoalanine synthase (β-CAS) pathway in cyanogenic plants provided the first insight on cyanide detoxification in nature. Fifty years of investigations firmly established the protective role of the β-CAS pathway in cyanogenic plants and its role in the removal of cyanide produced from ethylene synthesis in plants, but also revealed the importance of this pathway for plant growth and development and the integration of nitrogen and sulfur metabolism. This review describes the β-CAS pathway, its distribution across and within higher plants, and the diverse biological functions of the pathway in cyanide assimilation, plant growth and development, stress tolerance, regulation of cyanide and sulfide signalling, and nitrogen and sulfur metabolism. The collective roles of the β-CAS pathway highlight its potential evolutionary and ecological importance in plants.

Role of Diazotrophic Bacteria in Biological Nitrogen Fixation and Plant Growth Improvement

Though there is an abundant supply of nitrogen in the atmosphere, it cannot be used directly by the biological systems since it has to be combined with the element hydrogen before their incorporation. This process of nitrogen fixation (N₂-fixation) may be accomplished either chemically or biologically. Between the two elements, biological nitrogen fixation (BNF) is a microbiological process that converts atmospheric di-nitrogen (N₂) into plant-usable form. In this review, the genetics and mechanism of nitrogen fixation including genes responsible for it, their types and role in BNF are discussed in detail. Nitrogen fixation in the different agricultural systems using different methods is discussed to understand the actual rather than the potential N₂-fixation procedure. The mechanism by which the diazotrophic bacteria improve plant growth apart from nitrogen fixation such as inhibition of plant ethylene synthesis, improvement of nutrient uptake, stress tolerance enhancement, solubilization of inorganic phosphate and mineralization of organic phosphate is also discussed. Role of diazotrophic bacteria in the enhancement of nitrogen fixation is also dealt with suitable examples. This mini review attempts to address the importance of diazotrophic bacteria in nitrogen fixation and plant growth improvement.

Possible Role of 1-Aminocyclopropane-1-Carboxylate (ACC) Deaminase Activity of Sinorhizobium sp. BL3 on Symbiosis with Mung Bean and Determinate Nodule Senescence.

Sinorhizobium sp. BL3 forms symbiotic interactions with mung bean (Vigna radiata) and contains lrpL-acdS genes, which encode the 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme that cleaves ACC, a precursor of plant ethylene synthesis. Since ethylene interferes with nodule formation in some legumes and plays a role in senescence in plant cells, BL3-enhancing ACC deaminase activity (BL3+) and defective mutant (BL3−) strains were constructed in order to investigate the effects of this enzyme on symbiosis and nodule senescence. Nodulation competitiveness was weaker in BL3− than in the wild-type, but was stronger in BL3+. The inoculation of BL3− into mung bean resulted in less plant growth, a lower nodule dry weight, and smaller nodule number than those in the wild-type, whereas the inoculation of BL3+ had no marked effects. However, similar nitrogenase activity was observed with all treatments; it was strongly detected 3 weeks after the inoculation and gradually declined with time, indicating senescence. The rate of plant nodulation by BL3+ increased in a time-dependent manner. Nodules occupied by BL3− formed smaller symbiosomes, and bacteroid degradation was more prominent than that in the wild-type 7 weeks after the inoculation. Changes in biochemical molecules during nodulation were tracked by Fourier Transform Infrared (FT-IR) microspectroscopy, and the results obtained confirmed that aging processes differed in nodules occupied by BL3 and BL3−. This is the first study to show the possible role of ACC deaminase activity in senescence in determinate nodules. Our results suggest that an increase in ACC deaminase activity in this strain does not extend the lifespan of nodules, whereas the lack of this activity may accelerate nodule senescence.

Effect of Brevibacterium iodinum RS16 and Methylobacterium oryzae CBMB20 Inoculation on Seed Germination and Early Growth of Maize and Sorghum-sudangrass hybrid Seedling under Different Salinity Levels

Salinity is one of the most relevant abiotic factor limiting crop yield and its net primary productivity. In addition, salinity induces an increased stress ethylene synthesis in plants which, in turn, exacerbate the responses to the stressor. Bacterial single or co-inoculation effect was tested using previously characterized plant growth promoting (PGP) bacteria Brevibacterium iodinum RS16 and Methylobacterium oryzae CBMB20 on maize and sorghum-sudan grass hybrid under different concentrations of NaCl. Non-inoculated maize and sorghum-sudangrass hybrid showed 33.4% and 20.0% reduction in seed germination under highest NaCl (150 mM) level tested. However, under the same NaCl concentration, co-inoculation with B. iodinum RS16 and M. oryzae CBMB20 PGP strains increased the seed germination in maize (16.7%) and sorghum-sudangrass hybrid (4.4%). In Gnotobiotic growth pouch experiments conducted for maize and sorghum-sudangrass hybrid, co-inoculation of PGP B. iodinum RS16 and M. oryzae CBMB20 mitigated the salinity stress and promoted root length by 22.9% and 29.7%, respectively. Thus the results of this study could help in development of potential bioinoculants that may be suitable for crop production under saline conditions.

Ethylene-regulated (methylsulfanyl)alkanoate ester biosynthesis is likely to be modulated by precursor availability in Actinidia chinensis genotypes

The limiting steps of ethylene-dependent (methylsulfanyl)alkanoate ester biosynthesis have been investigated in this study, using closely related Actinidia chinensis genotypes and the commercial cultivar ‘Hort16A’. Quantification of methylsulfanyl-compounds from the headspace of ethylene-producing kiwifruits revealed little variation in their volatile composition but remarkable differences in the magnitude of the fruit volatile levels. To test whether the variations in fruit volatile levels can be correlated with the genotype-specific apparent catalytic efficiency, the initial slope of the substrate response curve ( V′ Max K M −1 where V′ Max is the apparent V Max in a crude extract) was evaluated for total alcohol acyltransferase (EC 2.3.1.84) activity. The V′ Max K M −1 values of different (methylsulfanyl)alkyl-CoAs were in a similar range for most genotypes, which suggests substrate availability as the limiting factor for (methylsulfanyl)alkanoate ester synthesis in these kiwifruit. Furthermore, gene expression analysis of acyltransferase expressed sequence tags points towards the action of multiple isozymes for (methylsulfanyl)alkanoate ester synthesis, emphasizing the central role of substrate levels on final ester concentrations. Volatile levels of the potential precursor methional were increased in ethylene-producing A. chinensis kiwifruit and a close connection between (methylsulfanyl)alkanoate ester formation and ethylene synthesis in plants is proposed. Finally, a possible biosynthetic pathway is presented.

The Sulfur-Containing Amino Acids: An Overview

Methionine, cysteine, homocysteine, and taurine are the 4 common sulfur-containing amino acids, but only the first 2 are incorporated into proteins. Sulfur belongs to the same group in the periodic table as oxygen but is much less electronegative. This difference accounts for some of the distinctive properties of the sulfur-containing amino acids. Methionine is the initiating amino acid in the synthesis of virtually all eukaryotic proteins; N-formylmethionine serves the same function in prokaryotes. Within proteins, many of the methionine residues are buried in the hydrophobic core, but some, which are exposed, are susceptible to oxidative damage. Cysteine, by virtue of its ability to form disulfide bonds, plays a crucial role in protein structure and in protein-folding pathways. Methionine metabolism begins with its activation to S-adenosylmethionine. This is a cofactor of extraordinary versatility, playing roles in methyl group transfer, 5'-deoxyadenosyl group transfer, polyamine synthesis, ethylene synthesis in plants, and many others. In animals, the great bulk of S-adenosylmethionine is used in methylation reactions. S-Adenosylhomocysteine, which is a product of these methyltransferases, gives rise to homocysteine. Homocysteine may be remethylated to methionine or converted to cysteine by the transsulfuration pathway. Methionine may also be metabolized by a transamination pathway. This pathway, which is significant only at high methionine concentrations, produces a number of toxic endproducts. Cysteine may be converted to such important products as glutathione and taurine. Taurine is present in many tissues at higher concentrations than any of the other amino acids. It is an essential nutrient for cats.

DOWN REGULATION OF ETHYLENE PRODUCTION AND SOFTENING IN ´MCINTOSH´ APPLES

Most 'Mclntosh' apples are produced for the fresh market and have to be stored under controlled atmosphere conditions to avoid rapid softening. The softening of fruits is the result of structural changes in the cell walls, caused by the activity of hydrolytic enzymes that are under the control of the ripening hormone ethylene. Ethylene is synthesized in plants from S-adenosyl-L-methionine by a short pathway that consists of two enzymes: 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and 1-amino-cyclopropane-1-carboxylic acid oxidase (ACO). To interfere with ethylene synthesis in plants we have cloned two ACS genes from ripening 'Mclntosh' apples. The gene showing the closest similarity to the ripening-related ACS gene in other fruits was used to make antisense constructs. 'Mclntosh' plants were transformed using an Agrobacterium-mediated transformation system. Transgenic plants were propagated on antibiotic-containing agar, transferred to the greenhouse for conditioning, and later to the field. Transgenic 'McIntosh' fruits which developed on these trees were evaluated for morphological characteristics, ethylene production, and ripening parameters. Down regulation of ethylene production that resulted in significant delay in softening was achieved in some transgenic lines resulting in improved storability. The data indicate that structural integrity of this fruit may be maintained simply under refrigerated storage and controlled humidity.

Plant Growth-Promoting Effects of Diazotrophs in the Rhizosphere

Because of their ability to transform atmospheric N2 into ammonia that can be used by the plant, researchers were originally very optimistic about the potential of associative diazotrophic bacteria to promote the growth of many cereals and grasses. However, multiple inoculation experiments during recent decades failed to show a substantial contribution of Biological Nitrogen Fixation (BNF) to plant growth in most cases. It is now clear that associative diazotrophs exert their positive effects on plant growth directly or indirectly through (a combination of) different mechanisms. Apart from fixing N2, diazotrophs can affect plant growth directly by the synthesis of phytohormones and vitamins, inhibition of plant ethylene synthesis, improved nutrient uptake, enhanced stress resistance, solubilization of inorganic phosphate and mineralization of organic phosphate. Indirectly, diazotrophs are able to decrease or prevent the deleterious effects of pathogenic microorganisms, mostly through the synthesis of antibiotics and/or fungicidal compounds, through competition for nutrients (for instance, by siderophore production) or by the induction of systemic resistance to pathogens. In addition, they can affect the plant indirectly by interacting with other beneficial microorganisms, for example, Azospirillum increasing nodulation of legumes by rhizobia. The further elucidation of the different mechanisms involved will help to make associative diazotrophs a valuable partner in future agriculture.

Inhibition of 1-aminocyclopropane-1-carboxylate oxidase by 2-oxoacids

An extract from ripe pear fruits was used to demonstrate that 1-aminocyclopropane-1-carboxylate (ACC) oxidase, the enzyme responsible for plant ethylene synthesis, is sensitive to inhibition by a range of 2-oxoacids, competitively with respect to the co-substrate ascorbic acid, and non-competitively with respect to ACC, and to the co-factors, iron (II) and carbon dioxide. The significance of the findings is discussed in terms of the reaction mechanism of ACC oxidase, an enzyme which is related by primary sequence to the family of iron (II)-dependent dioxygenases, most of which use 2-oxoglutarate as a co-substrate.

Characterization of the ethylene-forming enzyme partially purified from melon

The ethylene-forming enzyme, which is responsible for the final stage of ethylene synthesis in plants, has been partially purified from melon fruits. The enzyme has a molecular weight of 41 000, a pH optimum at about pH 7.5, an apparent K m of 60 μM, and although it resembles many 2-oxoglutarate-dependent dioxygenases in its requirement for ascorbate and Fe 2+, it does not require 2-oxoglutarate for activity. The enzyme is inhibited by SH-reagents, n-propyl gallate, 1,2-dihydroxynaphthalene, CO 2+, Ni 2+, Cu 2+, Zn 2+ and Mn 2+, but is insensitive to cycloheximide and protonophores.

Control of ethylene synthesis by expression of a bacterial enzyme in transgenic tomato plants.

Synthesis of the phytohormone ethylene is believed to be essential for many plant developmental processes. The control of ripening in climacteric fruits and vegetables is among the best characterized of these processes. One approach to reduce ethylene synthesis in plants is metabolism of its immediate precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). Soil bacteria containing an enzyme, ACC deaminase, were identified by their ability to grow on ACC as a sole nitrogen source. The gene encoding ACC deaminase was cloned and introduced into tomato plants. Reduction in ethylene synthesis in transgenic plants did not cause any apparent vegetative phenotypic abnormalities. However, fruits from these plants exhibited significant delays in ripening, and the mature fruits remained firm for at least 6 weeks longer than the nontransgenic control fruit. These results indicated that ACC deaminase is useful for examining the role of ethylene in many developmental and stress-related processes in plants as well as for extending the shelf life of fruits and vegetables whose ripening is mediated by ethylene.

Gravitropism in Plant Stems May Require Ethylene

Two inhibitors of ethylene synthesis in plants (cobaltous ion and aminoethoxyvinylglycine) and two inhibitors of ethylene action (silver ion and carbon dioxide) significantly delay the gravitropic response (upward bending) of mature dicot stems laid on their sides. This evidence suggests that ethylene may be required in the gravitropic response of shoots.

Regulation of wound ethylene synthesis in plants

Ethylene is produced by plants at specific stages of their life cycle and is involved in the regulation of many developmental processes, such as fruit ripening, flower fading, leaf abscission, growth in aquatic plants and initiation of flowering in bromeliads1,2. Ethylene is also formed when plants are subjected to stress by, for example, wounding, noxious chemicals, drought or waterlogging1–3. In both cases the biosynthetic pathway begins with methionine 1–5. It proceeds to ethylene by way of S-adenosylmethionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC), a recently discovered intermediate6,7, in ripening fruit7,8 and auxin-treated pea stem sections9,10. We now report that wound-induced ethylene synthesis also proceeds by way of ACC and that it is regulated at the level of the ACC-forming enzyme (ACC synthase). Wounding of pericarp tissue of tomato fruit (Lycopersicon esculentum Mill.) results in rapid enhancement of the activity of ACC synthase and, consequently, in a greatly increased rate of ACC synthesis.