Role of ethylene on various ripening pathways and on the development of sensory quality of Charentais cantaloupe melons

Charentais melons (Cucumis melo L., var cantalupensis Naud.) in which ethylene biosynthesis has been suppressed by an antisense ACC oxidase gene have been used to better understand the role of ethylene in the regulation of the ripening process of climacteric fruit and on the development of sensory qualities. We have shown that a number of biochemical and molecular processes associated with the ripening of climacteric fruit are ethylene-independent. In some cases, such as softening of the flesh, the same pathway comprises both ethylene-dependent and -independent components. The various ethylene-dependent events exhibit differential sensitivity to ethylene. The threshold level for degreening of the rind is 1 ppm, while 2.5 ppm are required to trigger the ethylene-dependent component of the softening process. The saturating level of ethylene for all these events is less than 5 ppm, which is by far lower than the internal ethylene concentrations found in the fruit at the climacteric peak (around 100 ppm). Detachment of the fruit influences the development of respiratory climacteric. Fruit remaining attached to the vine, although producing higher levels of ethylene, exhibit a reduced climacteric rise in respiration as compared to detached fruit. The response of antisense ACO fruit to exogenous ethylene in terms of respiration is higher in detached than in attached fruit. Ethylene-suppressed melons show a severe reduction of aroma volatiles production, particularly in ester production. In the biosynthetic pathway of aliphatic esters, the dehydrogenation of fatty acids and aldehydes appears to be ethylene-dependent. In contrast, alcohol acetylation comprises ethylene-dependent and ethylene-independent components, probably corresponding to differentially regulated alcohol acetyl transferases. In terms of sensory quality, these data show that the extension of shelf-life through the inhibition of ethylene production has some beneficial effects on texture and sugar accumulation but is detrimental for the generation of aroma

Cadmium-induced ethylene production and responses in Arabidopsis thaliana rely on ACS2 and ACS6 gene expression

Background: Anthropogenic activities cause metal pollution worldwide. Plants can absorb and accumulate these metals through their root system, inducing stress as a result of excess metal concentrations inside the plant. Ethylene is a regulator of multiple plant processes, and is affected by many biotic and abiotic stresses. Increased ethylene levels have been observed after exposure to excess metals but it remains unclear how the increased ethylene levels are achieved at the molecular level. In this study, the effects of cadmium (Cd) exposure on the production of ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and on the expression of the ACC Synthase (ACS) and ACC Oxidase (ACO) multigene families were investigated in Arabidopsis thaliana. Results: Increased ethylene release after Cd exposure was directly measurable in a system using rockwool-cultivated plants; enhanced levels of the ethylene precursor ACC together with higher mRNA levels of ethylene responsive genes: ACO2, ETR2 and ERF1 also indicated increased ethylene production in hydroponic culture. Regarding underlying mechanisms, it was found that the transcript levels of ACO2 and ACO4, the most abundantly expressed members of the ACO multigene family, were increased upon Cd exposure. ACC synthesis is the rate-limiting step in ethylene biosynthesis, and transcript levels of both ACS2 and ACS6 showed the highest increase and became the most abundant isoforms after Cd exposure, suggesting their importance in the Cd-induced increase of ethylene production. Conclusions: Cadmium induced the biosynthesis of ACC and ethylene in Arabidopsis thaliana plants mainly via the increased expression of ACS2 and ACS6. This was confirmed in the acs2-1acs6-1 double knockout mutants, which showed a decreased ethylene production, positively affecting leaf biomass and resulting in a delayed induction of ethylene responsive gene expressions without significant differences in Cd contents between wild-type and mutant plants

Recent Developments on the Role of Ethylene in the Ripening of Climacteric Fruit

It has long been recognised that ethylene plays a major role in the ripening process of climacteric fruit. A more thorough analysis, however, has revealed that a number of biochemical and molecular processes associated with climacteric fruit ripening are ethylene-independent. One of the crucial steps of the onset of ripening is the induction of autocatalytic ethylene production. In ethylene-suppressed melons, ACC synthase activity is induced at the same time as in control melons, indicating that ACC biosynthesis during the early stages of ripening seems to be a developmentally-regulated (ethylene-independent) process. The various ripening events exhibit differential sensitivity to ethylene. For instance, the threshold level for degreening of the rind is 1ppm, while 2.5 ppm are required to trigger some components of the softening process. The saturating level of ethylene producing maximum effects is less than 5 ppm, which is by far lower than the internal ethylene concentrations found in the fruit at the climacteric peak (over 100 ppm). In many fruit chilling temperatures hasten ethylene production and ripening and in some late season pear varieties, exposure to chilling temperatures is even absolutely required for the attainment of the capacity to synthesize autocatalytic ethylene. This is correlated with the stimulation of expression of ACC oxidase and of members of the ACC synthase gene family. Ethylene operates via a perception and transduction pathway to induce the expression of genes responsible for the biochemical and physiological changes observed during ripening. However, only a few genes induced via the ethylene transduction pathway have been described so far. We have used a differential display method to isolate novel ethylene-reponsive (ER) cDNA clones of tomato that potentially play a role in propagating the ethylene response and in regulating fruit ripening. Collectively, these data permit a general scheme of the molecular mechanisms of fruit ripening to be proposed

A dominant repressor version of the tomatoSl-ERF.B3gene confers ethylene hypersensitivity via feedback regulation of ethylene signaling and response components

Ethylene Response Factors (ERFs) are downstream components of the ethylene signal transduction pathway, although their role in ethylene-dependent developmental processes remains poorly understood. As the ethylene-inducible tomato Sl-ERF.B3 has been shown previously to display a strong binding affinity to GCC-box-containing promoters, its physiological significance was addressed here by a reverse genetics approach. However, classical up- and down-regulation strategies failed to give clear clues to its roles in planta, probably due to functional redundancy among ERF family members. Expression of a dominant repressor ERF.B3-SRDX version of Sl-ERF.B3 in the tomato resulted in pleiotropic ethylene responses and vegetative and reproductive growth phenotypes. The dominant repressor etiolated seedlings displayed partial constitutive ethylene response in the absence of ethylene and adult plants exhibited typical ethylene-related alterations such as leaf epinasty, premature flower senescence and accelerated fruit abscission. The multiple symptoms related to enhanced ethylene sensitivity correlated with the altered expression of ethylene biosynthesis and signaling genes and suggested the involvement of Sl-ERF.B3 in a feedback mechanism that regulates components of ethylene production and response. Moreover, Sl-ERF.B3 was shown to modulate the transcription of a set of ERFs and revealed the existence of a complex network interconnecting different ERF genes. Overall, the study indicated that Sl-ERF.B3 had a critical role in the regulation of multiple genes and identified a number of ERFs among its primary targets, consistent with the pleiotropic phenotypes displayed by the dominant repression lines

ER5, a tomato cDNA encoding an ethylene-responsive LEA-like protein: characterization and expression in response to drought, ABA and wounding

We report the isolation by differential display of a novel tomato ethylene-responsive cDNA, designated ER5. RT-PCR analysis of ER5 expression revealed an early (15 min) and transient induction by ethylene in tomato fruit, leaves and roots. ER5 mRNA accumulated during 2 h of ethylene treatment and thereafter underwent a dramatic decline leading to undetectable expression after 5 h of treatment. The full-length cDNA clone of 748 bp was obtained and DNA sequence analysis showed strong homologies to members of the atypical hydrophobic group of the LEA protein family. The predicted amino acid sequence shows 67%, 64%, 64%, and 61%sequence identity with the tomato Lemmi9, soybean D95-4, cotton Lea14-A, and resurrection plant pcC27-45 gene products, respectively. As with the other members of this group, ER5 encodes a predominantly hydrophobic protein. Prolonged drought stress stimulates ER5 expression in leaves and roots, while ABA induction of this ethylene-responsive clone is confined to the leaves. The use of 1-MCP, an inhibitor of ethylene action, indicates that the drought induction of ER5 is ethylene-mediated in tomato roots. Finally, wounding stimulates ER5 mRNA accumulation in leaves and roots. Among the Lea gene family this novel clone is the first to display an ethylene-regulated expression

A conserved phosphorylation site regulates the transcriptional function of ETHYLENE-INSENSITIVE3-like1 in tomato

ETHYLENE-INSENSITIVE3/ETHYLENE-INSENSITIVE3-like (EIN3/EIL) transcription factors are important downstream components of the ethylene transduction pathway known to regulate the transcription of early ethylene-responsive genes in plants. Previous studies have shown that phosphorylation can repress their transcriptional activity by promoting protein degradation. The present study identifies a new phosphorylation region named EPR1 (EIN3/EIL phosphorylation region 1) in tomato EIL1 proteins. The functional significance of EPR1 was tested by introducing mutations in this region of the Sl-EIL1 gene and by expressing these mutated versions in transgenic tomato plants. Transient expression data and phenotypic analysis of the transgenic lines indicated that EPR1 is essential for the transcriptional activity of Sl-EIL1. Moreover, mutation in the EPR1 site that prevents phosphorylation abolishes ethylene constitutive responses normally displayed by the Sl-EIL1-overexpressing lines. Bimolecular fluorescence complementation (BiFC) studies showed that the presence of a functional phosphorylation site within EPR1 is instrumental in the dimerization of Sl-EIL1 proteins. The results illuminate a new molecular mechanism for the control of EIN3/EIL activity and propose a model where phosphorylation within the EPR1 promotes the dimerization process allowing the initiation of EIL-mediated transcription of early ethylene-regulated genes

Transcriptional regulation of Banana EIN3-like genes: correlation with ethylene fruit responsiveness and ripening processes

Ethylene signal transduction initiates with ethylene binding at receptor proteins and terminates in a transcription cascade involving the EIN3/EIL transcription factors. In order to get more insights into the ethylene responsiveness process of banana fruit, we have isolated from banana fruit four cDNA homologs of the Arabidopsis EIN3/EIN3-Like gene, MaEILs (Musa acuminata ethylene insensitive 3-like). Sequence comparison with other banana EIL genes already registered in the database led us to conclude that, at this day, at least 5 different genes namely MaEIL1, MaEIL2/AB266318, MaEIL3/AB266319, MaEIL4/AB266320 and AB266321 exist in banana. Expression of these genes were further analysed in peel and pulp tissues, in relationship with changes of fruit ethylene responsiveness and ripening processes. MaEIL mRNAs were detected in all examined tissues but at lower level in peel than in pulp. According to tissues, MaEIL genes were differentially regulated by ripening and ethylene in mature green fruit. MaEIL2/AB266318 was the unique ripening- and ethylene-induced gene, MaEIL1, MaEIL4/AB266320 and AB266321 genes were down-regulated while MAEIL3/ AB266319 presented an unusual pattern of expression. Interestingly, a marked change was observed mainly on MaEIL1 and MaEIL3/AB266319 mRNA accumulation, concomitantly with changes in ethylene responsiveness of fruit. Data presented in this study suggest the importance of a transcriptionally step control in the regulation of EIL genes during banana fruit ripening. (Résumé d'auteur

Isolation and characterization of three members of the multigenic family encoding ACC oxidase from H. brasiliensis during plant development : [Draft]

Applying Ethephon, an ethylene releaser, to increase rubber production in H. brasiliensis has been practised for a long time. The effect of ethylene on latex production has been amply described, notably for lengthening latex flow and its regeneration. Nevertheless, little is known about the expression of genes involved in ethylene biosynthesis and response to ethylene. In this paper, we isolated and characterized genes encoding ACC oxidase, a key enzyme in ethylene biosynthesis in the plant. We then studied the effect of ethylene stimulation on the expression of ACO genes in various tissues during plant development. Three members of the ACO multigenic family were isolated from a bark cDNA library with RACE technology: HbACO-H4, HbACO-H5, and HbACO-O48. Full length cDNA sequences encoded for peptides of 318, 315, and 318 amino acids respectively for these 3 members, which had 79 to 92% protein identity and 75 to 86% nucleotide homology between them. Two genomic sequences were isolated: HbACO-H4, which was 1504 bp long and consisted of 2 introns and 3 exons, while Hb-ACO-H5 was 1456 bp long and consisted of 3 introns and 4 exons. These three genes were differentially expressed in different plant organs in response to ethylene stimulation. (Résumé d'auteur

A preliminary transcriptomic approach to elucidate post harvest ripening of plum fruit

The aim of the present study was to dissect common and/or diverse mechanisms regulating plum (Prunus salicina) fruit ripening in genotypes characterized by different patterns of ethylene production. Fruit of an ethylenesuppressed cultivar ('Shiro') and a cultivar characterized by the typical increase of ethylene production during fruit ripening ('Santa Rosa') were harvested at commercial maturity stage and allowed to further ripen at room temperature (23°C) up to 4 days. While non-detectable amounts of ethylene were recorded in 'Shiro' fruit, a typical climacteric behavior was observed in 'Santa Rosa' plums. For comparative purposes, the peach microarray μPEACH 1.0 containing 4,806 oligonucleotides corresponding to an equal number of genes expressed in peach fruit was employed for transcript profiling during postharvest ripening of both cultivars. Intriguingly, transcript levels of genes involved in ethylene biosynthesis, primarily 1-aminocyclopropane-1-carboxylate synthase, appeared to increase during the progress of 'Shiro' fruit ripening, following the same pattern as in 'Santa Rosa' plums. These data suggest that an induction of the ethylene biosynthetic pathway is present also in plum cultivars in which the burst of ethylene is not detectable. Expression levels of other genes implicated in auxin metabolism, antioxidant system and stress response followed the same pattern in both cultivars. Overall, this preliminary transcriptomic approach tried to elucidate the flow of events that accompany postharvest ripening of plum cultivars with diverse properties in relation to ethylene evolutio