Ethylene and fruit ripening

The latest advances in our understanding of the relationship between ethylene and fruit ripening are reviewed. Considerable progress has been made in the characterisation of genes encoding the key ethylene biosynthetic enzymes, ACC synthase (ACS) and ACC oxidase (ACO) and in the isolation of genes involved in the ethylene signal transduction pathway, particularly those encoding ethylene receptors ( ETR ). These have allowed the generation of transgenic fruit with reduced ethylene production and the identification of the Nr tomato ripening mutant as an ethylene receptor mutant. Through these tools, a clearer picture of the role of ethylene in fruit ripening is now emerging. In climacteric fruit, the transition to autocatalytic ethylene production appears to result from a series of events where developmentally regulated ACO and ACS gene expression initiates a rise in ethylene production, setting in motion the activation of autocatalytic ethylene production. Differential expression of ACS and ACO gene family members is probably involved in such a transition. Finally, we discuss evidence suggesting that the NR ethylene perception and transduction pathway is specific to a defined set of genes expressed in ripening climacteric fruit and that a distinct ETR pathway regulates other ethylene-regulated genes in both immature and ripening climacteric fruit as well as in non-climacteric fruit. The emerging picture is one where both ethylene-dependent and -independent pathways coexist in both climacteric and non-climacteric fruits. Further work is needed in order to dissect the molecular events involved in individual ripening processes and to understand the regulation of the expression of both ethylene-dependent and -independent genes.     

The Relationship between the Expression of Ethylene-Related Genes and Papaya Fruit Ripening Disorder Caused by Chilling Injury

Papaya (Carica papaya L.) is sensitive to low temperature and easy to be subjected to chilling injury, which causes fruit ripening disorder. This study aimed to investigate the relationship between the expression of genes related to ethylene and fruit ripening disorder caused by chilling injury. Papaya fruits were firstly stored at 7°C and 12°C for 25 and 30 days, respectively, then treated with exogenous ethylene and followed by ripening at 25°C for 5 days. Chilling injury symptoms such as pulp water soaking were observed in fruit stored at 7°C on 20 days, whereas the coloration and softening were completely blocked after 25 days, Large differences in the changes in the expression levels of twenty two genes involved in ethylene were seen during 7°C-storage with chilling injury. Those genes with altered expression could be divided into three groups: the group of genes that were up-regulated, including ACS1/2/3, EIN2, EIN3s/EIL1, CTR1/2/3, and ERF1/3/4; the group of genes that were down-regulated, including ACO3, ETR1, CTR4, EBF2, and ERF2; and the group of genes that were un-regulated, including ACO1/2, ERS, and EBF1. The results also showed that pulp firmness had a significantly positive correlation with the expression of ACS2, ACO1, CTR1/4, EIN3a/b, and EBF1/2 in fruit without chilling injury. This positive correlation was changed to negative one in fruit after storage at 7°C for 25 days with chilling injury. The coloring index displayed significantly negative correlations with the expression levels of ACS2, ACO1/2, CTR4, EIN3a/b, ERF3 in fruit without chilling injury, but these correlations were changed into the positive ones in fruit after storage at 7°C for 25 days with chilling injury. All together, these results indicate that these genes may play important roles in the abnormal softening and coloration with chilling injury in papaya.     

Regulation of the protein and gene expressions of ethylene biosynthesis enzymes under different temperature during peach fruit ripening

Ethylene has profound effect on fruit development and ripening, and the role of ethylene biosynthesis enzymes involving 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS), ACC oxidase (ACO), and S-Adenosyl-l-methionine synthetase (SAMS) in peach fruit (cv. Xiahui-8) was characterized under 25 and 4 °C, respectively. All these enzymes in ethylene synthesis pathway were identified using 2-DE and real-time PCR. Both protein and gene expressions of ACO and SAMS were much higher at 25 °C than at 4 °C. Among five members of ACS family, PpaACS4 may belong to system II ethylene biosynthesis, while PpaACS3 involved in system I during development stage, and low temperature can induce PpaACS1 expression. The ethylene release and low expressions of proteins and genes of most enzymes indicated that low temperature can effectively postpone ripening stage by reducing ethylene evolution. High gene expression of PpaSAMS did not cause excessive expression of SAMS protein under low temperature, and over-expression of PpaACS1 at low temperature still did not induce increase of ethylene production. The mechanism underlying the phenomenon about how temperature affects ethylene release was also discussed.     

Dose-dependent effects of malformin A1 on IAA-induced ethylene production in mung bean (Vigna radiate L.) hypocotyl segments

Purified malformin A1 (cyclo-D-Cys-D-Cys-L-Val-D-Leu-L-lle), a cyclicpentapeptide toxin fromAspergillus niger, was applied to the hypocotyl segments of mung bean (Vigna radiata L.) seedlings to investigate its role in regulating ethylene biosynthesis. Production of ethylene was induced by treating the plants with 0.1 mM indole-3-acetic acid (1AA). When 0.1 μM malformin A1 was then applied, ethylene production increased and the activities of two key enzymes for its biosynthesis, 1-aminocyclopropane-1-carboxylic acid (ACC)-synthase (ACS) and ACC-oxidase (ACO), were also stimulated. However, at levels of 1 or 10 μM malformin A1, both ethylene production and enzymatic activities were significantly reduced. In the case of ACO,in vitro activity was regulated by malformin A1, independent of ACS activity or the influence of IAA. Furthermore, the conjugate form of ACC, N-malonyl ACC, was significantly promoted by treatment with 0.1 μM malformin A1. These data suggest that malformin A1 can modulate ethylene production through diverse paths and that its effect depends on the concentration of the treatment administered.     

Manipulation of ethylene biosynthesis

The plant hormone ethylene is involved in many plant processes ranging from seed germination to leaf and flower senescence and fruit ripening. Ethylene is synthesized from methionine, via S-adenosyl-L-methionine (SAM) and 1-amino-cyclopropane-1-carboxylic acid (ACC). The key ethylene biosynthetic enzymes are ACC synthase (ACS) and ACC oxidase (ACO). Manipulation of ethylene biosynthesis by chemicals and gene technology is discussed. Biotechnological modification of ethylene synthesis is a promising method to prevent spoilage of agricultural and horticultural products.     

Effects of Chilling Temperatures on Ethylene Binding by Banana Fruit

Banana fruit are highly susceptible to chilling injury during low temperature storage. Experiments were conducted to compare ethylene binding during storage at chilling (3 and 8 °C) versus optimum (13 °C) temperatures. The skins of fruit stored at 3 and 8 °C gradually darkened as storage duration increased. This chilling effect was reflected in increasing membrane permeability as shown by increased relative electrolyte leakage from skin tissue. In contrast, banana fruit stored for 8 days at 13 °C showed no chilling injury symptoms. Exposure of banana fruit to the ethylene binding inhibitor 1-methylcyclopropene (1 l l^-1 1-MCP) prevented ripening. However, this treatment also enhanced the chilling injury accelerated the occurrence of chilling injury-associated increased membrane permeability. ¹⁴C-ethylene release assay showed that ethylene binding by banana fruit stored at low temperature decreased with reduced storage temperature and/or prolonged storage time. Fruit exposed to 1-MCP for 12 h and then stored at 3 or 8 °C exhibited lower ethylene binding than those stored at 13 °C. Thus, chilling injury of banana fruit stored at low temperature is associated with a decrease in ethylene binding. The ability of tissue to respond to ethylene is evidently reduced, thereby resulting in failure to ripen.     

G-protein-coupled alpha2A-adrenoreceptor agonists differentially alter citrus leaf and fruit abscission by affecting expression of ACC synthase and ACC oxidase

Temporal and spatial expression patterns of genes encoding 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS1 and ACS2) and ACC oxidase (ACO), ACC concentration, and ethylene production in leaves and fruit of 'Valencia' orange (Citrus sinensis [L.] Osbeck) were examined in relation to differential abscission after treatment with 2-chloroethylphosphonic acid (ethephon) alone or in combination with guanfacine or clonidine, two G-protein-coupled alpha(2A)-adrenoreceptor selective agonists. Guanfacine and clonidine markedly reduced ethephon-enhanced leaf abscission, but had little effect on ethephon-enhanced fruit loosening. Ethephon-enhanced fruit and leaf ethylene production, and ACC concentration in fruit abscission zones, fruit peel, leaf abscission zones, and leaf blades were decreased by guanfacine. Guanfacine reduced ethephon-enhanced expression of ACS1 and ACO genes in leaf abscission zones and blades, but to a lesser extent in fruit abscission zones. The expression pattern of the ACS2 gene, however, was not associated with abscission. The results demonstrate that differential expression of ACS1 and ACO genes is associated with reduction of ethephon-enhanced leaf abscission by guanfacine, and suggest a link between G-protein-related signalling and abscission.     

The role of ethylene in the prevention of chilling injury in nectarines

Woolliness is a chilling injury phenomenon occurring in nectarines held at low temperatures for extended periods. It is a disorder marked by altered cell wall metabolism during ripening leading to a dry, woolly texture in the fruit. Two treatments were found to alleviate this disorder. One was holding the fruits for 2 days at 20 °C before 0 °C storage (delayed storage) and the second was having ethylene present during cold storage (ethylene). Immediately stored fruit (control) had 88 percnt; woolliness while 7 percnt; of delayed storage and 15 percnt; of ethylene fruit showed woolliness. The severity of the injury in individual fruits was closely related to inhibition of ethylene evolution. Woolly fruit had higher levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and less 1-aminocyclopropane-1-carboxylic acid oxidase (ACO, EC 1.4.3) activity than healthy fruit. It is suggested that ethylene is essential for promoting the proper sequence of cell wall hydrolysis necessary for normal fruit softening. This is in contrast to chilling injury in other fruits, whereby ethylene is often a sign of incipient damage. Respiration was also found to be associated with chilling injury, in that fruit with woolliness had a depressed respiration.     

GhXB38D represses cotton fibre elongation through ubiquitination of ethylene biosynthesis enzymes GhACS4 and GhACO1

Ethylene plays an essential role in the development of cotton fibres. Ethylene biosynthesis in plants is elaborately regulated by the activities of key enzymes, 1-aminocyclopropane-1-carboxylate oxidase (ACO) and 1-aminocyclopropane-1-carboxylate synthase (ACS); however, the potential mechanism of post-translational modification of ACO and ACS to control ethylene synthesis in cotton fibres remains unclear. Here, we identify an E3 ubiquitin ligase, GhXB38D, that regulates ethylene biosynthesis during fibre elongation in cotton. GhXB38D gene is highly expressed in cotton fibres during the rapid elongation stage. Suppressing GhXB38D expression in cotton significantly enhanced fibre elongation and length, accompanied by the up-regulation of genes associated with ethylene signalling and fibre elongation. We demonstrated that GhXB38D interacts with the ethylene biosynthesis enzymes GhACS4 and GhACO1 in elongating fibres and specifically mediates their ubiquitination and degradation. The inhibition of GhXB38D gene expression increased the stability of GhACS4 and GhACO1 proteins in cotton fibres and ovules, resulting in an elevated concentration of ethylene. Our findings highlight the role of GhXB38D as a regulator of ethylene synthesis by ubiquitinating ACS4 and ACO1 proteins and modulating their stability. GhXB38D acts as a negative regulator of fibre elongation and serves as a potential target for enhancing cotton fibre yield and quality through gene editing strategy.     

Exogenous Eethylene influences flower opening of cut roses (Rosa hybrida) by regulating the genes encoding ethylene biosynthesis enzymes

1 Introduction The simple gaseous phytohormone ethylene as apotent modulator has various roles in plant growth,development and in response to biotic and abioticstress, such as germination, fruit ripening, flower andleaf senescence, and responsiveness to pathogen attack and mechanical damage[1]. The opening and senes-cence of many kinds of flowers are correlated tightly to ethylene, including carnation, petunia, orchid and rose[2]. Generally, roses are classified as ethylene-sen-sitive, however…     

Recovery of ethylene biosynthesis in diazocyclopentadiene (DACP)-treated tomato fruit

Diazocyclopentadiene (DACP), a competitive ethylene action inhibitor binds irreversibly to the ethylene receptor to reduce tissue responses to ethylene. Tomato fruit (Lycopersicon esculentum Mill cv lsquo;Rondellorsquo;) were treated with DACP at the mature green stage. Ethylene biosynthesis and respiration rate were depressed. Color changes from green to red were delayed. Compared to the control, ACC content increased and ACC oxidase activity in vivo decreased in DACP-treated fruit. Thus, decrease of ethylene production caused by DACP treatment was due to the reduction of ACC oxidase activity. The decline in ripening subsequently recovered after DACP treatment. Results from the Northern analysis for gene expression of ACC synthase and ACC oxidase, showed that expression of both genes declined in DACP-treated fruit, and then recovered. Therefore the recovery of ethylene production was due to the recovery in gene expression and activity of ACC oxidase. We conclude that the effects of DACP on ethylene biosynthesis are on expression of ACC synthase and ACC oxidase genes, and/or regulation of ACC oxidase activity.     

Exogenous ethylene influences flower opening of cut roses (<Emphasis Type="Italic">Rosa hybrida</Emphasis>) by regulating the genes encoding ethylene biosynthesis enzymes

The purpose of this paper is to investigate the differential responses of flower opening to ethylene in two cut rose cultivars, ‘Samantha’, whose opening process is promoted, and ‘Kardinal’, whose opening process is inhibited by ethylene. Ethylene production and 1-aminocyclopropane-1-carboxylate (ACC) synthase and oxidase activities were determined first. After ethylene treatment, ethylene production, ACC synthase (ACS) and ACC oxidase (ACO) activities in petals increased and peaked at the earlier stage (stage 3) in ‘Samantha’, and they were much more dramatically enhanced and peaked at the later stage (stage 4) in ‘Kardinal’ than control during vasing. cDNA fragments of three Rh-ACSs and one Rh-ACO genes were cloned and designated as Rh-ACS1, Rh-ACS2, Rh-ACS3 and Rh-ACO1 respectively. Northern blotting analysis revealed that, among three genes of ACS, ethylene-induced expression patterns of Rh-ACS3 gene corresponded to ACS activity and ethylene production in both cultivars. A more dramatic accumulation of Rh-ACS3 mRNA was induced by ethylene in ‘Kardinal’ than that of ‘Samantha’. As an ethylene action inhibitor, STS at concentration of 0.2 mmol/L generally inhibited the expression of Rh-ACSs and Rh-ACO in both cultivars, although it induced the expression of Rh-ACS3 transiently in ‘Kardinal’. Our results suggests that ‘Kardinal’ is more sensitive to ethylene than ‘Samantha’; and the changes of Rh-ACS3 expression caused by ethylene might be related to the acceleration of flower opening in ‘Samantha’ and the inhibition in ‘Kardinal’. Additional results indicated that three Rh-ACSs genes were differentially associated with flower opening and senescence as well as wounding.     

Inhibition of ethylene biosynthesis by antisense ACC oxidase RNA prevents chilling injury in Charentais cantaloupe melons

Non-freezing low temperature storage causes injury to melons and most other fruit and vegetables of tropical and subtropical origin. We demonstrate here that ethylene suppression through an antisense ACC oxidase (ACO) gene considerably reduced the sensitivity of Charentais cantaloupe melons to chilling injury. In contrast to wild-type fruit, antisense ACO melons did not develop the characteristic chilling injury of pitting and browning of the rind neither when stored at low temperature (3 weeks at 2 °C) nor upon rewarming. Treating antisense melons with 10 p.p.m. ethylene for more than 1 d prior to cold storage resulted in the restoration of chilling sensitivity. When the ethylene treatment was performed after cold storage, the chilling injury symptoms did not appear. The tolerance to chilling was associated with a lower accumulation of ethanol and acetaldehyde, reduced membrane deterioration and higher capacity of the fruit to remove active oxygen species. The activities of catalase, superoxide dismutase and peroxidase were markedly increased in antisense ACO fruit in comparison with wild-type fruit, particulary upon rewarming and post-storage ethylene treatment. Severe chilling injury symptoms were correlated with a lower activity of activated oxygen scavenging enzymes. These results demonstrate that ethylene acts in conjunction with low temperature to induce metabolic shifts that participate in the development of chilling injury.     

Involvement of ethylene biosynthesis and perception in the susceptibility of citrus fruits to Penicillium digitatum infection and the accumulation of defence-related mRNAs

Citrus fruits infected with the fungus Penicillium digitatum substantially increase the production of the plant hormone ethylene. In this study, the regulation of ethylene biosynthesis in Citrus sinensis-infected fruits and its putative involvement in an active defence response against P. digitatum infection is examined. Ethylene production is demonstrated as being the result of the co-ordinated and differential up-regulation of at least three ethylene biosynthetic genes: ACS1, ACS2, and ACO. Blocking ethylene perception by 1-MCP resulted in an increased ethylene production and ACS2 expression during infection and mechanical wounding, suggesting that this gene is negatively regulated by ethylene. ACO expression was induced by ethylene in the absence of wounding or infection, although further results indicate that its induction during the course of infection may not be primarily mediated by ethylene. Treatment with 1-MCP also increased susceptibility to Penicillium decay, showing an involvement of ethylene perception in promoting defence responses in citrus fruits. The changes in the expression of two defence-related genes up-regulated during infection were also studied: the ones coding for phenylalanine ammonia-lyase (PAL) and an acidic class II chitinase (ACR311). The onset of PAL expression after mechanical wounding or inoculation was not changed in 1-MCP-pretreated fruits, while its later increase during the course of infection was abolished. Chitinase gene induction was more related to mechanical damage and was partially repressed by ethylene. These studies indicate distinct possible regulatory mechanisms of plant fruit defence genes in the context of fungal infection and ethylene perception.