As mentioned above, ethylene interacts with ABA and GAs, both hormones being essential regulators of germination and dormancy Feurtado and Kermode, ; Nambara et al. Thus, the improving effect of ethylene may occur via the involvement of C 2 H 4 -GAs-ABA crosstalk but whether its action is direct or indirect needs clarification.
Figure 2 summarizes the current data concerning ABA-GAs-C 2 H 4 networks based on genetic analyses, microarray data, and physiological studies. It would be then important to discriminate the hierarchy of the different signaling pathways, and their role as sensor of environmental signals. Interactions between ethylene, abscisic acid, gibberellins, and ROS in the regulation of seed germination and dormancy.
This scheme is based on genetic analyses, microarray data, and physiological studies on seed responsiveness to ethylene, ABA, GAs, or ROS cited in the text. Ethylene down-regulates ABA accumulation by both inhibiting its synthesis and promoting its inactivation or catabolism, and also negatively regulates ABA signaling. Ethylene also improves the GAs metabolism, and GAs signaling, and vice versa. Whether ROS are signals induced by environmental factors to modulate the hormonal network toward germination is to be investigated.
Omics studies are now available in the field of seed germination but efforts to develop transcriptomic analysis of ethylene action are required to understand ethylene involvement in seed germination.
Analysis of the effects of ethylene on specific cellular processes highlighted by dormancy and germination studies such as transcription regulation, cell cycle activity and endosperm weakening should help to understand the regulatory network of germination process in seeds. Moreover, although hormonal signaling network share common components, they may work in specific territories in seeds. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Flower development occurs through a series of sequential steps required for the cell proliferation proper regulation, expansion, and the reproductive tissue development. The expression of ethylene biosynthesis genes seems to be linked to the formation of particular flower tissues. In the China rose Hibiscus rosa-sinensis , ACS and ACO were found to be specifically expressed in developing style—stigma plus stamen and ovary tissues Trivellini et al.
Similar evidence has been reported in carnation Dianthus caryophyllus and petunia Tang et al. Ethylene receptors are involved in reproductive organ development. In China rose HrsETR and HrsERS transcript levels were differentially expressed in the bud flower stage in style-stigma plus stamen, petals and ovary with different temporal patterns suggesting a possible tissue-specific role Trivellini et al.
In Arabidopsis , ETR2 receptor was developmentally regulated in the inflorescence, floral meristems, and developing petals and ovules Sakai et al. Flower development occurs with the specification of floral identity in shoot meristem and then floral organ primordial initiates and rises to the formation of sepal, petal, stamen, carpel, and ovule. The development of floral organ is controlled by homeotic genes during reproductive phase.
Each of these steps involves elaborate networks of factors that regulate floral morphogenesis. A potential genetic network involving ethylene as a regulator of flower development and homeotic genes has been emerging. In silver vase A. In tomato, the ectopic expression of LeHB-1 was reported to disrupt flower development, suggesting a critical role in floral organogenesis Lin et al. Moreover, the global transcriptome profile showed that several MADS-box genes regulating floral identity as well as genes related to ethylene response were affected in ufd mutant inflorescences.
These results suggest that ethylene signaling may interact with the development of flower primordia and UFD may have a key function as a positive regulator of floral organ identity and growth genes, together with hormonal signaling pathways. The present section gives an insight into the interaction of ethylene with other hormones during flower development. Auxins may influence flowering in plants by affecting ethylene evolution. In a classical study, Burg and Burg reported that auxin-induced flowering in pineapple by stimulating ethylene formation.
Treatment of pineapple plants with naphthalene acetic acid NAA enhanced ethylene levels. However, this is an exceptional case, and ethylene generally inhibits flowering in many plant species, including Arabidopsis and pharbitis Ipomoea nil , synonym Pharbitis nil Achard et al.
Achard et al. Both the induction and inhibition of flowering have been reported by IAA, inhibition in SD plants cultivated under an inductive photoperiod, whereas stimulation in long-day LD plants under non-inductive conditions Kulikowska-Gulewska et al. ABA plays an important role in the photoperiodic induction of flowering in pharbitis seedlings, and the inhibitory effect of ethylene on pharbitis flowering inhibition may depend on its influence on the ABA level. The inhibition of flowering was observed when ABA was applied just before or at the beginning of a h-long dark period Wilmowicz et al.
Moreover, the application of AVG partially reversed the inhibitory effect of ABA on flowering, suggesting that ABA influenced ethylene production which directly inhibited flowering.
Thus, ABA could affect flowering indirectly by modifying other hormones. In Arabidopsis, ABA-deficient mutants aba and aba have a late flowering phenotype Riboni et al.
Various GAs, such as GA 32 and 2,2-dimethyl G 4 , are especially florigenic when applied to non-induced Darnel ryegrass Lolium temulentum plants Pharis et al. The treatment of GA to the foliar bud of japtropha Jatropha curcas increased the number of female flowers and fastened the flower development due to an increased endogenous level of GA and auxin.
In contrast, ethrel ethylene source treatment decreased flower development due to the decreased endogenous level of auxin, while GA treatment significantly increased it Makwana and Robin, Lee et al. The pulses of GAs especially GA 1 may have different effects on floral initiation according to the time of day that they occur. The diurnal rhythm might be one way by which the absence of phytochrome B causes early flowering in 58M phytochrome B null mutant under most photoperiods.
The expression of key oxidase genes in the biosynthesis of gibberellin, gibberellin 20 oxidase 2 GA20OX2 is high in flowers and siliques, as is the expression of GA20OX3 Phillips et al. However, Mitchum et al. The GA-deficient mutant, gal-3 , which is severely defective in ent-kaurene production Zeevaart and Talon, flowers later than the Thale cress Landsberg erecta wild type in a long day but is totally unable to flower in SD unless treated with exogenous GA 3 Wilson et al.
Although it is quite apparent that GA governs flowering in plants, however, its independence of ethylene is also an important question to be addressed. The growth of plants in the presence of an ethylene precursor ACC or in an ethylene-enriched atmosphere delayed WT flowering Achard et al. These findings were the basis for the current model for integration of the ethylene and GA—DELLA signaling pathways in the regulation of the floral transition Achard et al.
Previous analyses have shown that CTR1 is the major negative regulator of ethylene signaling Kieber et al. A study of Achard et al. Moreover, the ethylene-mediated inhibition of CTR1 activity resulted in a reduction in bioactive GA levels, causing increased accumulation of DELLAs, a family of nuclear growth repressor proteins Achard et al.
Transcript meta-analysis suggests that applying exogenous ethylene to plants represses the expression of GA metabolism genes. Conversely, upon treatment with GAs, the expression of some ethylene synthesis genes is up-regulated. At reduced ethylene levels, the growth of gai-t6 rga double loss-of-function mutants is more resistant to the effects of ACC than the wild type.
Ethylene up-and down-regulates different GA biosynthesis and catabolism genes in Arabidopsis seedlings Vandenbussche et al. The life of flowers is genetically determined due to their role in sexual reproduction and fertilization, and the maintenance of floral structure has a considerable cost in terms of respiratory energy, nutrients, and water loss Stead, ; Jones et al.
The flowers are therefore programmed to senesce after pollination or when the stigma is no longer receptive. In fact, young and mature petals are sinks, and only after pollination, when fertilization and fruit set are accomplished, a controlled senescence program allows important nutrients to be salvaged from dying tissue, from the petal to the developing ovary or transported to other sink tissues i.
Flower senescence involves an ordered set of events coordinated at tissue and cellular level that can be regulated by endogenous signals, such as plant hormones, and by environmental factors, such as temperature, nutrients, light, and pathogen attack. All major plant hormones have been reported to affect flower senescence, with ethylene, jasmonic acid, salicylic acid SA , ABA, and brassinosteroids as inducers and with cytokinins, GA, and auxin as inhibitors Reid and Chen, Ethylene is known to be a key player of plant aging, including fruit ripening, and flower and leaf senescence Abeles et al.
Ethylene in flower petals is involved in the inhibition of cell expansion through the regulation of water channel proteins aquaporin that facilitate the passage of water through biological membranes Ma et al.
The crucial role of aquaporins in flower development suggests that cellular collapse during the flower aging process might be regulated by transcellular and the transmembrane water transport which are important for motor cell dynamics.
This condition might be supported by the massive transcriptional regulation of over genes encoding for aquaporins among different flower developmental stages, from anthesis to senescence, in China rose Trivellini et al.
A large number of flowers are affected by ethylene, but sensitivity to ethylene varies according to species and cultivars Van Doorn, In many ethylene sensitive species, pollination triggers senescence leading to a climacteric rise in ethylene production, which becomes autocatalytic and coordinates cellular events among and within the different floral tissues, leading to wilt, fade, and abscise Woltering and Van Doorn, The use of pharmacological treatments affect at different levels the ethylene signaling pathway, [i.
For example, the exogenous application of ethylene or its biosynthetic precursor such as ACC accelerates corolla senescence in China rose flowers Trivellini et al.
On the other hand, senescence can significantly delayed the treatment of flowers with inhibitors of ethylene biosynthesis, such as AOA Trivellini et al. Their suppression by antisense technology has been successful in prolonging floral display life. The down-regulation of the ACS and ACO genes in carnation reduced ethylene production and was effective in delaying floral senescence Savin et al.
The antisense transformations of ethylene biosynthetic genes have been successfully attempted in other ornamental species including petunia Huang et al. ACS is the rate-limiting enzyme of ethylene biosynthesis in plants Wang et al. A positive feedback regulation, in senescing the China rose flowers through an increase in ethylene production among the different flower organs Trivellini et al.
Recently, the global transcriptome profiling of China rose reveals that the senescence is caused by the enhancement of signals that would naturally occur via transcriptional upregulation of the ethylene biosynthetic pathway during aging Trivellini et al. In addition to the transcripts associated with biosynthetic genes ACO and ACS , also the ethylene response factors ERFs were differentially regulated among flower tissues during senescence Figure 1.
Schematic representation of flower senescence in H. Data from Trivellini et al. Red and blue indicate up-regulation and down-regulation, respectively. Ethylene perception mechanism and its signaling pathway are based on the presence of its receptors, which are essential to carry on the aging process Kieber et al. The alteration of ethylene signaling by transformations of several ornamental species such as campanula, dianthus and kalanchoe with the ETR1 mutated gene under control of the flower-specific promoters resulted in plants with considerably higher ethylene tolerance and a better flower longevity Gubrium et al.
Moreover, transgenic petunia plants with reduced PhEIN2 expression exhibited significant delays in flower senescence Shibuya et al. And in Arabidopsis , a mutation in the CTR1 gene causes a constitutive ethylene response and early senescence and abscission of the flowers Huang et al. Moreover, the suppression of PhGRL2 by VIGS system conferred an accelerated flower senescence phenotype with enhanced ethylene production, and when PhGRL2 was transiently overexpressed in petunia buds, the ethylene production was reduced and the longevity of flowers treated with 35Spro:PhGRL2 was significantly prolonged.
EIN3-regulated genes trigger a diverse array of ethylene responses Solano et al. Recently, silencing an ERF petunia transcription factor homeodomain-leucine zipper protein PhHD-Zip dramatically reduced ethylene production and the abundance of transcripts of genes involved in ethylene ACS , ACO and led to an increase in flower longevity Chang et al.
The dynamic activation of transcription factors during flower senescence is a key mechanism that controls the age-dependent expression of several senescence-related genes.
These transcription factors, in turn, regulate the expression levels of various genes that may influence the ethylene pathway indirectly Olsen et al.
In addition to studies which describe the influence of the individual ethylene hormone on flower senescence, there are also reports that describe the importance of hormonal interactions. Previous studies have shown that either exogenous application Taverner et al. The overproduction of cytokinins in petunia flowers transformed with P -S AG IPT has been reported to delay corolla senescence and decrease sensitivity to ethylene Chang et al.
An increase in ethylene, in petunia flowers exogenously treated with cytokinin, was found during senescence, and the lack of a negative effect can be explained considering the expression of the ethylene receptors was down-regulated by treatment with BA Trivellini et al. Similarly, the application of thidiazuron, a cytokinin-like compound, enhanced ethylene production but simultaneously extended vase life by inhibiting leaf yellowing in cut stock flowers Ferrante et al.
These results suggest that despite the enhanced ethylene production, flowers that accumulated cytokinins showed an increased flower longevity. In contrast, exogenous cytokinins delayed senescence, suggesting they might play a role in the regulation of the time of senescence Van Doorn et al. The HD—Zip I transcription factors are unique to plants and have been reported to be involved in various plant development responses, including flower senescence Xu et al.
Moreover, the silencing of the key regulatory enzyme in the GA biosynthetic pathway, RhGA20ox1 accelerated the senescence in rose petals. Another recent study suggests that a reduction in the bioactive GA content enhances the ethylene-mediated flower senescence Yin et al.
In this study, the overexpression of a basic helix-loop-helix bHLH transcription factor, PhFBH4 , increased the abundance of transcripts of ethylene biosynthesis genes and also increased ethylene production. Another study reported that the transcriptome changes associated with delayed flower senescence on transgenic petunia by inducing the expression of etr , down-regulated genes involved in gibberellin biosynthesis, response to gibberellins stimulus, and ethylene biosynthesis, at different time points Wang H.
Similarly to the ethylene, ABA accumulation accelerates the senescence of cut flowers and flowering potted plants Ferrante et al. In rose, ABA was reported to increase the sensitivity of flowers to ethylene, as the gene expression of some ethylene receptors increased after exogenous ABA treatment Muller et al.
The over-expression of PhHD-Zip accelerated petunia flower senescence and this condition is another example highlighting the interaction of different hormones Chang et al. These results suggest that PhHD-Zip plays an important role in regulating petunia flower senescence. Moreover, a transcriptome study reported that several genes involved in ABA biosynthesis, catabolism, and signaling pathways were induced by exogenous cytokinins BA treatment Trivellini et al. In the experiment reported by Chang et al.
These results suggest that in addition to the ethylene pathway, the cytokinins seem to be strongly involved in the regulation of ABA biosynthesis and its degradation in flower tissues, thus ABA plays a primary role in petunia flower senescence. The fruit is the development of the ovary after the fertilization and protects the seeds until complete maturation. The seeds represent the germ plasm of the plants and are responsible for the dissemination of the species. From an ecological point of view, fruits during the unripe stage represent an organ that must be protected from insects or frugivores.
A fruit must be unattractive and its green color allows the camouflage itself with leaves. The ripening of fruits is a unique coordination of various biochemical and developmental pathways regulated by ethylene, which affects color, texture, nutritional quality and aroma of fruits Barry and Giovannoni, During ripening in climacteric fruits, the ethylene regulates firmness and color changes involving chlorophyll reduction, increase in carotenoids or anthocyanins, sugars, and biosynthesis of volatile organic compounds VOCs.
Ethylene is tightly correlated with the VOCs biosynthesis, which increases in ripe fruit and enhances the attraction of frugivores.
The inhibition of ethylene biosynthesis reduces production of VOCs and reduces the aroma of fruits Figure 2. It has been found that transgenic apples expressing antisense genes for ACS or ACO produced lower VOCs and in particular, the strongest reduction was observed in the esters, which were 3—4 fold lower compared with WT Dandekar et al. The exogenous application of ethylene reconverted the VOCs evolution. This result indicates that ethylene inhibits the key steps of volatile biosynthesis.
The study with the application of 1-MCP or AVG demonstrated that ethylene regulates VOCs biosynthesis directly through the pathway of volatile biosynthesis and indirectly through the ethylene perception. In fact, apricots Prunus armeniaca treated with ethylene biosynthesis inhibitor, such as AVG, strongly reduced the VOCs biosynthesis, while the 1-MCP, an ethylene action inhibitor, enhanced the evolution of aldehydes Valdes et al.
A Schematic and simplified ethylene and VOCs biosynthesis during fruit development. VOCs biosynthesis derive from different pathways such as phenylpropanoids, fatty acid, and carotenoids degradation. B The main enzymes involved in cell wall degradation during fruit ripening and senescence. The action of these enzymes induces loss of firmness and softening.
In climacteric fruits, ethylene biosynthesis increases and shows a peak corresponding to respiration pattern, while in non-climacteric fruits the ethylene declines with fruit ripening and senescence.
The tomato has been used as a model plant for studying the role of ethylene in fruit ripening. The transition from unripe to ripe fruit induces several biochemical changes that involve ethylene biosynthesis and perception. Unripe fruits produce a low amount of ethylene and are insensitive to exogenous ethylene.
Hence, ethylene treatments do not induce the fruit ripening system 1. At the beginning of ripening, ethylene production increases and induces an increase of autocatalytic biosynthesis.
These fruits, in this development stage, if exposed to exogenous ethylene show a burst of ethylene production and ripen faster system 2. Fruits are classified in system 1 when they produce a low amount of ethylene and tissues are insensitive to exogenous ethylene Alexander and Grierson, The delay of ethylene increase is the most common strategy used in post-harvest for prolonging the storage and increasing the shelf life. The inhibition of ethylene biosynthesis or action usually leads to an extension of shelf life of the climacteric fruits.
Ethylene regulates fruit ripening by affecting the ACS and ACO genes and the fruit specific polygalacturonase, involved in the depolymerization of cell wall pectin during ripening Smith et al. It affects pectin methylesterase PME , which provides accessibility to pectin by polygalacturonase and phytoene synthase responsible for the pigmentation of many fruits and flowers Koch and Nevins, ; Fray and Grierson, Cloned mRNAs that accumulate in the unripe tomato fruits exposed to exogenous ethylene were investigated through blot hybridization experiment.
The expression of cloned genes was developmentally regulated by the ethylene during fruit ripening, with more mRNAs produced by these genes in ripe fruits than in unripe fruits and the increase in mRNA was repressed by norbornadiene, an ethylene action inhibitor Lincoln et al. Gene expression analysis of Never-ripe Nr and additional tomato receptor homologs indicated that Nr and LeETR4 transcripts were most abundant in the ripen fruit tissues Zhou et al.
Alba et al. The mutation of the ethylene receptor Nr , which reduces ethylene sensitivity and inhibits ripening, also influenced fruit morphology, seed number, ascorbate accumulation, carotenoid biosynthesis, ethylene evolution, and the expression of many genes during fruit maturation, indicating that ethylene governed multiple aspects of development both prior and during fruit ripening in tomato Alba et al.
In tomato, the E8 gene plays a role in the negative regulation of ethylene biosynthesis through repression of ethylene signal transduction.
The expression of the gene increased during ripening and its antisense repression resulted in an increased ethylene evolution but delayed ripening Penarrubia et al. The relationship between ethylene and auxin in the fruit development has been studied.
Auxins are involved in fruit development and inhibit ripening Brady, The exogenous application of auxins in different fruits delayed the senescence such as observed in Bartlett pears Pyrus communis ; Frenkel and Dyck, , banana Musa acuminate ; Purgatto et al.
The application of auxin lowered the ethylene production in sliced apples Malus domestica , if applied at pre-climacteric phase, while enhancing its biosynthesis at the climacteric stage Lieberman et al.
There exists a crosstalk between auxin and ethylene; and Bleecker and Kende pointed out that auxins can stimulate the biosynthesis of more climacteric ethylene through its inductive action on the expression of the key enzyme ACS Abel and Theologis, Ethylene and auxins are tightly related during fruit senescence.
The free auxin increases during senescence and stimulates ethylene biosynthesis. Further studies are required to understand the ethylene sensitivity changes after 1-MCP treatment. The nature and transcriptional response of CTG led to discovering a rise in free auxin in the 1-MCP treated fruits.
The exogenous application of cytokinins or compounds with cytokinins-like activity increased the sugar content of fruits and induced earlier ripening. Recent studies have shown that CPPU delayed the ethylene increase during fruit ripening and also delayed central placenta softening Ainalidou et al.
In avocado, the application of isopentenyl adenosine increased the ethylene and fruit ripening Bower and Cutting, The studies regarding the role of cytokinins in the plant senescence are available in the literature, but the relationship between cytokinins and ethylene during fruit ripening and senescence has not yet completely been elucidated and needs further investigations.
In tomato fruit, ABA biosynthesis occurs via carotenoids degradation pathways and the key enzyme is the 9- cis -epoxycarotenoid dioxygenase NCED. The ABA content increases following the biosynthesis of carotenoids during ripening. These changes are associated with ripening and also with ethylene production.
The exogenous application of ABA increases ethylene biosynthesis Mou et al. These results suggest that ABA can be a trigger for ethylene production and influence fruit ripening Zhang et al. In banana fruit, ABA stimulates ripening independently from the ethylene.
ABA application increases all hydrolases, which can enhance the softening, with exception to the polygalacturonase activity Lohani et al. Interestingly, these authors provide new insights into the regulatory mechanism underlying tomato fruit development and ripening with the ethylene involved in the downstream signal transduction of ABA and sucrose, as a negative regulator of ASR gene expression, which influenced the expression of several cell wall and ripening-related genes leading to fruit softening.
The relationship of other phytohormones such as ABA and GA with ethylene during fruit senescence needs to be elucidated. The loss of firmness or softening of fruits is a very important quality parameter. The softening is due to cell wall degradation induced from several enzymes that are synergistically activated. Almost all these enzymes are encoded by multi-genes family, which regulates the spatial-temporal activation of these enzymes.
Ethylene plays a crucial role in regulating these genes and enzymes during ripening and senescence. The cell wall degradation is facilitated by expansins that are proteins, which are involved in the enlargement of cell matrix. This phenomenon occurs during cell wall growth and disruption. The action of these enzymes has been found to be tightly associated with the fruit ripening and senescence Civello et al. The expansins are tightly dependent on pH. The transcription of these enzymes is carried out by gene families, which have been isolated and characterized in several plant species.
Different isoforms can provide the expansins action during plant growth and fruit senescence, linking the development stage with the activation of specific isoforms. The inhibition of ethylene biosynthesis also reduced and inhibited the EXP1 gene expression Rose et al. The activation of the expansin EXP1 has also been shown in other climacteric fruits such as banana Trivedi and Nath, Pectin methylesterase is an enzyme activated before fruit ripening and catalyzes the de-esterification of pectin, by removing the methyl group C-6 of galacturonic acid and allows the polygalacturonase action.
The PME has an important role during fruit senescence and cell wall degradation with loss of firmness. This enzyme is stimulated by ethylene and inhibited by ethylene inhibitors such as 1-MCP El-Sharkawy et al.
This enzyme is activated after the action of PME and is also induced by ethylene. In antisense ACC synthase tomato, the exposure to ethylene rapidly increased transcript accumulation of the PG. The gene expression of PG was directly correlated with ethylene concentrations used Sitrit and Bennett, Bananas treated with ethylene increased the activity of this enzyme, while the use of 1-MCP reduced its activity Lohani et al. Analogous results were observed in mango treated with ethylene for inducing ripening or treated with 1-MCP for delaying ripening Chourasia et al.
The cell wall degrading enzymes is sequentially activated during ripening and senescence. Ethylene is one key regulator of these enzymes at transcriptional and post-transcriptional level Figures 2A,B. It may be summarized that ethylene plays a key role in plant growth and development.
The action of ethylene in the growth and development may not be isolated. It triggers the network of signaling pathways and influences through the interaction with other phytohormones regulation of several processes.
The understanding of the crosstalk between ethylene and other phytohormones in regulating growth and senescence could provide a promising strategy to manipulate the content of these hormones through molecular techniques in order to get specific plant responses. During plant life, the transition from vegetative to reproductive stages and senescence is largely influenced by ethylene and its interplay with other plant hormones. This networking not only influences the ethylene concentration but also tissues sensitivity.
There are few studies focusing on the molecular changes in plant tissues after the combined treatments of ethylene with other plant hormones. These studies should be extended to different organs and development stages to deeply understand the intricate network affecting relevant agronomic traits such as yield, longevity, and appearance morphology.
The discovery of new synergistic or antagonist relationships among ethylene and other hormones can have great potential to support cell division and differentiation processes during plant development, to enhance crop yield by delaying aging and prolong shelf-life of flowers and maintain the quality of climacteric fruits. Moreover, the equilibrium between the ethylene biosynthesis and its perception influences the crop adaptability and performance under different stress conditions.
It has been shown that other plant hormones can positively or negatively influence this equilibrium. The interplay of ethylene and plant hormones on plant performance should also be investigated at the post-translation level. NI and MK wrote on the role of ethylene in leaf, flower and fruit growth and development and its interaction with other hormones in the process, together with the introduction. NK suggested the concept of the manuscript, wrote the abstract and looked over the whole manuscript order and language and contributed to the overall look of the manuscript.
AFe, AT, and AFr wrote on the role of ethylene in leaf, flower and fruit senescence and its interaction with other hormones in the process. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer BVDP and handling Editor declared their shared affiliation, and the handling Editor states that the process nevertheless met the standards of a fair and objective review. Abel, S.
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