Bouzayen, Mondher

Chang, Caren

Kalaitzis, Panagiotis

Kanellis, Angelos

Mattoo, Autar

Van Der Straeten, Dominique

Zhang, Jin-Song

English

Ghent University Academic Bibliography

EDITORIALpublished: 12 March 2020doi: 10.3389/fpls.2020.00248Frontiers in Plant Science | www.frontiersin.org 1 March 2020 | Volume 11 | Article 248Edited and reviewed by:Gerrit T. S. Beemster,University of Antwerp, Belgium*Correspondence:Dominique Van Der Straetendominique.vanderstraeten@ugent.beSpecialty section:This article was submitted toPlant Physiology,a section of the journalFrontiers in Plant ScienceReceived: 21 January 2020Accepted: 18 February 2020Published: 12 March 2020Citation:Van Der Straeten D, Kanellis A,Kalaitzis P, Bouzayen M, Chang C,Mattoo A and Zhang J-S (2020)Editorial: Ethylene Biology andBeyond: Novel Insights in the EthylenePathway and Its Interactions.Front. Plant Sci. 11:248.doi: 10.3389/fpls.2020.00248Editorial: Ethylene Biology andBeyond: Novel Insights in theEthylene Pathway and ItsInteractionsDominique Van Der Straeten 1*, Angelos Kanellis 2, Panagiotis Kalaitzis 3,Mondher Bouzayen 4, Caren Chang 5, Autar Mattoo 6 and Jin-Song Zhang 71 Laboratory of Functional Plant Biology, Department of Biology, Ghent University, Ghent, Belgium, 2 Laboratory ofPharmacognosy, Department of Pharmaceutical Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece,3Department of Horticultural Genetics and Biotechnology, Mediterranean Agronomic Institute of Chania, Chania, Greece,4 INRA Génomique et Biotechnologie des Fruits (GBF), Toulouse, France, 5Department of Cell Biology and MolecularGenetics, University of Maryland, College Park, MD, United States, 6 Beltsville Agricultural Research Center, AgriculturalResearch Service (USDA), Beltsville, MD, United States, 7 Institute of Genetics and Developmental Biology, Chinese Academyof Sciences (CAS), Beijing, ChinaKeywords: ethylene, ACC (1-aminocyclopropane-1-carboxylic acid), stress, ACC synthase (ACS), ACC oxidase(ACO), gold standardEditorial on the Research TopicEthylene Biology and Beyond: Novel Insights in the Ethylene Pathway and Its InteractionsThis Research Topic presents selected contributions to Ethylene 2018, the XI InternationalSymposium on the Plant Hormone Ethylene, held in Chania, Greece, on 2nd−6th June 2018,covering exciting new discoveries in the ethylene field.This issue brings novel insights in ethylene signaling in bacteria, algae, and lower plants as wellas evidence supporting a specific role for the ethylene precursor 1-aminocyclopropane-1-carboxylicacid (ACC) in plants.Ethylene receptors were initially thought to be specific to plants. Interestingly, ethylene receptorhomologs have been found in cyanobacteria. It was previously shown that in Synechocystis sp.an ethylene receptor regulates phototaxis and biofilm formation. In this issue, the same group(Allen et al.) demonstrates that another cyanobacterium, the filamentous species Geitlerinema sp.which possesses two ethylene receptor homologs, similarly displays ethylene-dependent alterationsin phototaxis, suggesting that such signaling could be prevalent in cyanobacteria. Both species arehighly sensitive to ethylene although their ethylene binding characteristics resemble that of plants,thus suggesting signal amplification in cyanobacteria.In higher plants, subfamily-I of the Arabidopsis receptors (ETR1 and ERS1) and theirinteractions with downstream players have been extensively studied, while information onsubfamily-II (ETR2, ERS2, and EIN4) remains sparse. Here, Berleth et al. demonstrate that ETR2displays comparable affinities for CTR1 and EIN2 to that previously reported for ETR1, suggestingsimilar protein-protein interaction-mediated signal transfer for both subfamilies. In addition, theauthors show enhanced stability of type-II receptor homomers and type-II:type-I heteromers ascompared to type-I homomers, emphasizing the importance of type-II receptors.Wang and Qiao present a mini-review on the transcriptional regulation of the ethylene responsein Arabidopsis. Ethylene signaling involves numerous regulatory steps leading to a diversity ofresponses in plant growth and development. This review discusses our current understanding ofthe transcriptional regulation as a major control point in ethylene signaling, focusing on recentinsights into the role of chromatin modification in repressing transcription.Van Der Straeten et al. Ethylene Biology and BeyondDolgikh et al. summarize recent advances on the molecularmechanisms that underlie EIN3/EIL1-directed ethylene signalingin Arabidopsis, and focus on the role of EIN3/EIL in tuningtranscriptional regulation of ethylene response in time and space.Furthermore, they consider the role of EIN3/EIL1-independentregulation of ethylene signaling.Qin et al. review hormonal crosstalk of ethylene in primaryroot growth of Arabidopsis and rice. Based on the proposedmodel, ethylene restricts primary root growth by governing auxinbiosynthesis, transport, and signaling through EIN3/EIL1, ERF1,and HB52 interactions in Arabidopsis. ABA and CKs constrainprimary root growth by controlling the posttranscriptionalregulation of ACS resulting in stimulated ethylene synthesis.GA and ethylene antagonistically regulate stability of DELLAproteins, which act as growth repressors. Low levels of BRshinder ethylene synthesis by BZR1 and BES1 suppressed ACSgene expression, while high levels of BRs increase ACS stability.Through a different mechanism, ethylene restricts primary rootgrowth in rice, by augmenting auxin and ABA biosynthesis.Understanding light-dependent differences in ethylene synthesisand signaling is essential to expand our insight into the roles ofethylene in growth and development across the plant life cycle.Harkey et al. performed a meta-analysis of multipletranscriptomic datasets to uncover responses to ethylenethat are both light-dependent and light-independent. A set of139 transcripts with robust and consistent responses to elevatedethylene across root-specific datasets was identified. This “goldstandard” group of ethylene-regulated transcripts includesnumerous genes encoding proteins that function in ethylenesignaling and synthesis. The study further reveals a numberof previously uncharacterized factors that may contribute toethylene response phenotypes.Plants synthesize ethylene in a two-step reaction startingwith the conversion of S-adenosyl-L-methionine (SAM) to1-aminocyclopropane-1-carboxylic acid (ACC). Vanderstraetenet al. demonstrated that ACC affects early vegetative developmentindependently of ethylene signaling. Using ethylene biosynthesisand signaling inhibitors, as well as mutants, ACC-specificethylene-independent growth responses in both dark- and light-grown Arabidopsis seedlings were revealed. Hence, researchersemploying ACC as an ethylene precursor should be mindfulof putative ACC effects confounding ethylene responses invegetative growth. The exact mechanism underlying the ACCresponse remains to be identified.While ACC may play an ethylene-independent role in plantgrowth and development, the three-membered ring amino-acidis probably also of paramount importance in the balanced co-existence of plants and beneficial micro-organisms around them,surmounting attacks of pathogens.Though the genome of the pathogenic fungus Fusariumgraminearum, which infects wheat, seems to lack genes encodingethylene biosynthetic enzymes, Svoboda et al. identified twoACC deaminase genes, one of which encodes an activeACC deaminase. Considering that ethylene insensitive wheatexhibited higher resistance to Fusarium and reduced mycotoxincontent, Fusarium knockouts of both genes were generated.No differences in the fungal infection and mycotoxin contentwere detected indicating that ethylene might not affect fullFusarium virulence.Nonaka et al. used ACC deaminase in a Super-Agrobacteriumstrain to enhance transformation efficiencies of recalcitrantspecies. Super-Agrobacterium was updated to version 4 byintroducing both an ACC deaminase and GABA transaminasegene, encoding enzymes that degrade ACC and GABA,respectively. The use of this modified strain resulted insubstantial reduction of the amount of time and labor requiredfor transformations, hence providing a more powerful tool forplant genetic engineering and functional analysis.While most studies have focused on the conversion of SAMto ACC by ACC synthases, there has been increasing interestin the subsequent step, carried out by ACC oxidases (ACOs).Houben and Van de Poel provide a comprehensive and historicalperspective on our understanding of the ACO enzyme, includingits discovery, activity, evolution, expression, regulation andpotential biotechnological applications.A thorough analysis of players in ethylene signaling enabledidentification of key regulators in fruit development andripening. Not unexpectedly, translational regulation of ethylenebiosynthesis and signaling appears to be fundamental in thecontrol of ethylene effects, besides transcriptional regulation.Mitalo et al. show that many aspects of kiwifruit ripeningcan be triggered by ethylene treatment or by low temperature,with the exception of aroma volatile production, a majorripening feature contributing to fruit quality, that is lacking incold-triggered ripening. The data indicate that the productionof aroma compounds is strongly ethylene-dependent andsupport the notion that in kiwifruit ethylene and lowtemperature-induced ripening may involve two differentregulatory mechanisms.Chen et al. used a modification of parallel reactionmonitoring, a targeted mass spectrometry proteomic method,to study ETR receptor abundance in tomato fruit. Focusing onsingle peptides of rare proteins, they compared the abundanceof ETRs in WT and in the NR mutant. Pearson correlationsbetween mRNA and protein profiles were used as indicatorsto discriminate the two genotypes and reveal changes overfruit development. It is proposed as an approach to study ETRsubfunctionalization across the plant kingdom in developmentas well as in plant-microorganism interactions.Regarding the role of ethylene in pigmentation, Khunmuanget al. demonstrate that ethylene-mediated petal color fading incut Vanda “Sansai Blue” flowers results from degradation ofanthocyanidins, cyaniding, and delphinidin, and is not relatedto the levels of flavonols, such as kaempferol. The endogenousanthocyanin degradation process stimulated by ethylene appearsrelated to increased peroxidase activity but was independent offlower senescence. Espley et al. investigated the incidence ofinternal browning flesh disorder (IBFD) in high anthocyaninred apples (Malus x domestica). The study, using the highlypigmented “Royal Gala” apple cultivar over-expressing MYB10,revealed that the anthocyanin-related transcription factor isassociated with the undesirable fruit disorder. The MYB10transgenic fruit had a high incidence of IBFD compared towild type. Interestingly, MYB10-expressor apple had higherFrontiers in Plant Science | www.frontiersin.org 2 March 2020 | Volume 11 | Article 248Van Der Straeten et al. Ethylene Biology and Beyondexpression of ethylene-related genes ACS, ACO, and ERF.Prematurely induced ethylene can advance fruit maturity and, asshown by these authors, may lead to adverse effects on storage ofhigh-anthocyanin fruits.Hormonal pathways are not functioning as independentroutes, but rather contribute to an information web,connecting internal signaling to transduction pathways ofexternal cues. Ethylene is involved in such an intricatenetwork which fine-tunes development from cell andorgan specification to senescence and abscission, but alsoincorporates external signals enabling plasticity in an everchanging environment, and controlling reactions to adverseconditions, such as those encountered as a result of globalclimate change.External factors such as wind, hale or snow, and/or growthon uneven terrain, induces tension wood formation in order toreorient and uplift the stem toward its original growth position.Tension wood is characterized by the presence of gelatinous,cellulose-rich (G-)fibers with its microfibrils oriented parallel tothe fiber cell axis. Seyfferth et al. demonstrated that ethyleneregulates transcriptional responses related to the amount ofG-fiber formation and their properties, including chemistry andcellulose microfibril angle, in hybrid aspen. The quantitative andqualitative changes in G-fibers are likely to contribute to upliftingof stems.Given the importance of ethylene in agricultural applicationsand the need for sustainable crop production, on the field aswell as in post-harvest control of fruits and vegetables, recentresearch has also focused on improved control of ethylene releaseand sensitivity, as well as on long-term storage conditions ofcrop products.AUTHOR CONTRIBUTIONSAll authors listed have made a substantial, direct and intellectualcontribution to the work, and approved it for publication.Conflict of Interest: The authors declare that the research was conducted in theabsence of any commercial or financial relationships that could be construed as apotential conflict of interest.Copyright © 2020 Van Der Straeten, Kanellis, Kalaitzis, Bouzayen, Chang, Mattooand Zhang. This is an open-access article distributed under the terms of the CreativeCommons Attribution License (CC BY). The use, distribution or reproduction inother forums is permitted, provided the original author(s) and the copyright owner(s)are credited and that the original publication in this journal is cited, in accordancewith accepted academic practice. No use, distribution or reproduction is permittedwhich does not comply with these terms.Frontiers in Plant Science | www.frontiersin.org 3 March 2020 | Volume 11 | Article 248

Editorial : Ethylene biology and beyond : novel insights in the ethylene pathway and its interactions

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Editorial : Ethylene biology and beyond : novel insights in the ethylene pathway and its interactions

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