Microbial modulation of plant ethylene signaling: ecological and evolutionary consequences
© The Author(s). 2018
Received: 9 November 2017
Accepted: 5 March 2018
Published: 21 March 2018
The plant hormone ethylene is one of the central regulators of plant development and stress resistance. Optimal ethylene signaling is essential for plant fitness and is under strong selection pressure. Plants upregulate ethylene production in response to stress, and this hormone triggers defense mechanisms. Due to the pleiotropic effects of ethylene, adjusting stress responses to maximize resistance, while minimizing costs, is a central determinant of plant fitness. Ethylene signaling is influenced by the plant-associated microbiome. We therefore argue that the regulation, physiology, and evolution of the ethylene signaling can best be viewed as the interactive result of plant genotype and associated microbiota. In this article, we summarize the current knowledge on ethylene signaling and recapitulate the multiple ways microorganisms interfere with it. We present ethylene signaling as a model system for holobiont-level evolution of plant phenotype: this cascade is tractable, extremely well studied from both a plant and a microbial perspective, and regulates fundamental components of plant life history. We finally discuss the potential impacts of ethylene modulation microorganisms on plant ecology and evolution. We assert that ethylene signaling cannot be fully appreciated without considering microbiota as integral regulatory actors, and we more generally suggest that plant ecophysiology and evolution can only be fully understood in the light of plant-microbiome interactions.
Environmental stress and plant fitness
Plants are constantly facing a range of different environmental stressors linked for instance to temperature, water availability, presence of toxic minerals, or pathogens. Stress can be permanent, for instance, when a plant lives outside its ecological optimum, or acute during climatic extremes such as drought and flooding waves. Environmental stress has an important effect on plant fitness and elicits specific adaptations . Plants have evolved a range of physiological and morphological responses to stressors, allowing them to cope with the prevailing environmental conditions. Although these responses vary widely, they all share one characteristic: they all come at a cost to the plant, diverting resources from growth and reproduction, and causing negative side effects that may have consequences on other traits that can result in indirect fitness costs. Optimizing the relative investment into stress response and other life history traits is thus essential to maximize fitness . Due to the variability of stressors and their interactive effects with plant genotype, regulating stress response is a complex task with several possible optima. Further, adaptation to one specific set of environmental conditions may negatively affect plant fitness under other conditions . Plant transpiration illustrates this dilemma well: stomatal closure, a typical plant response to drought, reduces water loss, but comes at a cost of lower photosynthesis, gas exchange and sap flow. Given that stomata are also an entry point for several pathogens , the optimal aperture will be a function of several parameters including water availability, plant sensitivity to desiccation, and presence of pathogens .
To optimize fitness, stress responses must be therefore carefully adjusted. This implies that plants need to perceive different stressors, process the signals, and trigger an optimal stress response, thereby maximizing resistance while minimizing costs and side effects. Signal integration in plants is generally achieved by alterations in hormonal balance. Hormones such as ethylene, auxin, or jasmonic acid interactively shape the relative investment of plants into growth, reproduction, and stress defense . Hormone concentrations are dictated by the combined action of the plant’s own regulatory pathways as well as the activities of its associated microbiota. Hormonal regulation therefore offers an excellent model to approach plant physiology, ecology, and evolution from a holobiont perspective in which plants and microbes form a coherent unit of selection .
In this review, we approach ethylene, a central plant hormone regulating the balance between growth and stress tolerance, from a holobiont perspective. We first briefly, summarize the importance of ethylene for stress tolerance and other life history traits. We then go on to provide an overview of how plants and their associated microbiota jointly shape hormonal balances, thereby shifting plant response toward or away from adaptation to specific situations.
Regulation of stress response by plants
Role of ethylene
Ethylene is a central plant hormone regulating several aspects of plant growth and development, throughout the whole plant life cycle, from germination to senescence . In addition, this hormone is essential to regulate stress responses and confer stress tolerance [9, 10]. Stress results in increased levels of ethylene in plants. Stress-derived ethylene is a signal triggering adaptive responses and influences other hormonal signaling pathways . Due to the multiple effects of ethylene on plant phenotype, increased ethylene levels will induce a range of pleiotropic effects, such as growth inhibition and late flowering , in addition to the target response . Precisely controlling cellular ethylene levels is thus a key aspect of plant physiology .
Ethylene production, signal transduction, and response
Ethylene varies as a function of stress type and intensity
Ethylene production depends on the intensity and duration of stress periods. For instance, different levels of heavy metal [25, 27] or different dehydration rates  differentially modulate ethylene biosynthesis and signaling. In another example, low-levels of stress stimulate ethylene production, while high levels may decrease it [28, 29], either as part of a targeted stress response or as the result of impaired plant metabolism.
Ethylene response from ecological and agricultural perspective
Ethylene variation in plants
Variability in ethylene-based stress responses across plant species
The core ethylene transduction cascade is highly conserved in plants, and a wide range of plants use ethylene as a regulator of their stress responses. However, plants vary greatly in how ethylene impacts stress perception, transduction, and the final response. Plants evolved in a certain environment have adapted ethylene signaling to the stresses typical for that environment or even dropped it, if not useful. For instance, plants living in flood-prone or riparian areas, including rice and Rumex palustris, use flooding-induced accumulation of ethylene to trigger important adaptive responses . In contrast, some aquatic plants adapted to a permanently submerged lifestyle and lost many genes involved in ethylene signaling [32, 33]. Contrasting ethylene-mediated responses are even seen in closely related plant species. For instance, different species of Rumex sp. or different varieties of rice all use ethylene as a flooding signal to trigger adaptive responses, yet the responses itself are highly variable, ranging from compensatory growth to complete quiescence [31, 34].
Variability in stress perception and ethylene signal transduction
Both ACS and ACO ethylene biosynthetic genes are encoded by large multigene families. These genes are organ-specific and are differentially regulated by different environmental signals [15, 35, 36]. The size of these multigene families can vary between plant species and could link to the variation in ethylene-mediated stress perception. For instance, apple harbors 19 ACS genes as compared to 12 ACS genes in Arabidopsis thaliana and 9 in tomato [36–38]. Deletion of one single gene, ACS6, resulted for instance in a 85–90% reduction in ethylene production in maize . Variation in the ethylene response can also occur at the level of ethylene perception across different plant genotypes linked to changes in receptor affinity, expression pattern, and/or turn-over . Furthermore, knocking out EIN3 showed opposite effects on salinity tolerance in Arabidopsis and rice . Ethylene signaling and response are highly dependent on plant genotype , organ, growth stage , and associated microbiota.
Importance of microbiota as co-regulator of stress response
Plants are associated with a complex microbiome, including bacteria, fungi, and protists that have impact on diverse aspects of plant growth, health, and evolution . Plant-associated microbiota can be either vertically transmitted, as is the case for endophytes that live within plant tissues, or horizontally for instance by recruiting microbiota to the rhizosphere from the surrounding soil species pool. Microbiota form an integral part of a plant’s immune system, metabolism, and hormonal balance . They directly alleviate stress, for instance, by producing protective compounds that enhance drought resistance [34, 46], by degrading organic pollutants , or by chelating heavy metals . Plant-associated microbes can also fine-tune hormonal balance and physiology by modulated plant hormone levels and the pathways they steer. In the case of ethylene, several possible mechanisms have been described by which microorganisms can affect plant hormonal levels. Below, we examine the mechanisms by which the plant-microbe dialog determines ethylene-mediated plant responses as the basis for a more general model on holobiont-level regulation of plant hormonal balance.
Ethylene modulation as a holobiome process
Ethylene signaling forms a perfect example of a holobiont-level physiological cascade. From the holobiont perspective, plant physiology is controlled by a combination of traits encoded in the host genome as well as its associated microbes, which collectively form the holobiont . This association offers a broader genetic pool than the plant alone: ethylene-modulating microbes could increase the reservoir of genetic information linked to ethylene signaling, enabling a greater plant phenotypic plasticity in response to stressors. The microbiota can (1) impact plant-perceived stress, (2) co-regulate ethylene which affects plant fitness, and (3) perceive ethylene, potentially responding to it.
Plant and ethylene-modulating microbes as unit of selection
Ethylene levels are a strong determinant of fitness in dynamic environments. Given that plants and microbes work in concert to modulate ethylene-mediated responses, the holobiont level of selection is the most appropriate: the ethylene cascade provides an important link between the host and its associated microbes, and forms an integrated biological entity . This interaction even has the potential to be evolutionarily stable: plants rely on microbes to optimize their fitness and microbes directly benefit from a more vigorous host that may provide more nutrients and energy. As plants can select associated microbes on the basis of the functions they perform, mutualistic interactions may persist across generations.
Ethylene modulation by microorganisms: evolutionary impact on plants
Reduction of stress perception by microorganisms
Alteration of ethylene level by microorganisms
Microbes can potentially influence all regulatory steps of the ethylene pathway (Fig. 2). The most direct way of acting on ethylene signaling is to either directly produce or degrade ethylene. Several plant-associated microbes can increase plant ethylene levels by directly synthesizing ethylene or inducing plant ACS activity [49–52]. Ethylene production by microbes was first reported in the pathogen Ralstonia solanacearum, which, among other symptoms, induces banana premature ripening . Microbial ethylene production was later mainly investigated in relation to pathogenic bacteria [50, 51]. However, biosynthetic pathway studies  and the examination of available bacterial genomes have revealed that the relevant genes and pathways can be found across a wide range of microorganisms [54, 55]. For instance, more than one third of all cultivable soil bacteria can produce ethylene via different pathways . Phylogenetic studies of ethylene-forming enzymes show that multiple ethylene-producing pathways have evolved independently and later spread between bacterial phyla by horizontal gene transfer [53, 56]. Ethylene production by microbes may have deep effects on plant physiology and life history, as demonstrated by the accelerated fruit ripening in plants inoculated with Escherichia coli engineered to produce ACC oxidase . Rhizosphere microbes can further increase ethylene indirectly by secreting auxin [58, 59] and cytokinin [58, 60], two hormones that upregulate the expression of ACS-coding genes [61, 62].
Microbioorganisms can also decrease ethylene levels, for instance, by producing ACC deaminase. This enzyme degrades ACC, ultimately leading to lower plant ethylene concentrations. ACC deaminase can be found in both commensal  and pathogenic microbes . ACC deaminase genes are widespread in bacteria, fungi, and members of stramenopiles . ACC deaminase genes of bacteria and fungi shared high sequence identity , pointing to a single evolutionary origin and frequent horizontal transfer of this gene in bacteria and fungi [65–67]. The reduction of ethylene levels caused by ACC-deaminase producing microbes is of the same magnitude as the one resulting from knocking out ACS genes [39, 68]. In contrast to commonly held assumptions, ACC deaminase-producing microbes are not necessarily good and the effects of ACC deaminase on plant physiology and plant growth greatly depend on the interactive effects of plant genotype [69, 70] and the environment [68, 71]. For instance, root growth reduction by ethylene is a common adaptation to avoid salt and pollutants . Alleviating this inhibition may bring a short-term increase in root growth, but may ultimately be deleterious for the plant.
Co-evolution of plants with bacteria that increase or inhibit ethylene levels may have various consequences: co-evolution of plants with microbes increasing ethylene levels may cause the plant to reduce ethylene production in order to maintain homeostasis. This could result in a lower ability to produce ethylene, a higher sensitivity to stressors and a dependency on microbial ethylene production (Fig. 3d). In contrast, plants associated with ethylene-reducing microorganisms such as ACC deaminase producers may need to produce more ACC to compensate for microbial degradation (Fig. 3c). Thus, plants may evolve a higher expression of ACS genes, which can not only allow a wide range of responses, but may also lead to overreactions to stress without modulation by the associated microbiome.
Microbial alteration of plant ethylene response and intertwined signaling
In addition to direct manipulation of ethylene levels, the microbiota is an integral component of stress perception and response. For instance, some microbial species can perceive environmental stressors relevant to the plant  as well as sense and respond to plant ethylene . This suggests that they may potentially be part of the holobiont-level ethylene-regulated traits, communicating stress perception to plants, and monitoring plant stress status. As ethylene sensitivity in plant-associated microbiota is widespread, we propose that ethylene signaling may be part of a hologenome-level stress response in which genetic traits carried by both microbiota and the plant are activated in response to stressors. Ethylene modulation is under this perspective the result of the co-evolution of both plant and microbial traits. Bacteria could receive signals from environment or plants and trigger plant ethylene response factors (Fig. 3e) or even express their own ethylene response factors in response to plant ethylene or environmental cues (Fig. 3f).
Such intertwined signaling between plants and microbes might contribute to complete  or a partial  loss of plant ethylene pathways over the course of evolution, as observed in the loss of the ACC biosynthetic route in several gymnosperms  or the production of ethylene via an ACC-independent pathway in several plants . From a co-evolutionary perspective, such plants will become more dependent on microbiota for ethylene pathway modulation.
What makes co-evolution possible?
Plants live in close association with a wide range of microbes. Roots select and feed a specific microbiome . A wide range of the rhizosphere-enriched microorganisms have the ability to modulate plant ethylene signaling. For instance, genes linked to ethylene production or reduction can be found in a broad range of bacteria and fungi [65, 78, 79]. The constant contact with an ethylene signaling-altering microbiota may cause the evolution of a modified pathway optimizing plant response in the presence of external perturbations.
Positive feedback loops: under stressful conditions, plants produce more ACC . This confers an advantage to microorganisms producing ACC deaminases that are able to use ACC as a nitrogen and carbon source. This may result in an increased density of ACC-degrading microbes, whose effect can be counteracted by the plant by producing more ACC. The outcome might be beneficial only for microbes (parasitism of plant nitrogen), or mutually beneficial (symbiosis via shared ethylene signaling).
Plant adaptation to fluctuating environments requires a rapid rewiring of stress response pathways such as ethylene signaling. However, this adaptation may be too slow in plants, requiring several generations to acquire and spread the needed mutations. Emergence of genetic variation in the microbiome is many orders of magnitude faster than in plants . Modulation of plant hormone levels via the microbiome may thus provide a new mechanism to match plant phenotype to environmental conditions.
Modulation of plant hormone levels via the microbiome may thus provide a new mechanism to match plant phenotype to environmental conditions.
Ethylene-modulating microorganisms can be transmitted vertically, from one generation to the next generation, thus allowing co-evolution of microbes and the host as a cohesive unit of selection . Vertical co-evolution may allow more gene transfer to the next generation, and the establishment of relatively stable associations. Nonetheless, vertical transmission is probably essential for the last of our proposed co-evolutionary dynamics (intertwined signaling; Fig. 3e, f). The ethylene modulation genes could transfer between ethylene-modulating bacteria by horizontal transfer [66, 67] and through symbiotic island exchange .
Evolutionary implications of ethylene manipulation by plant-associated microorganisms
Alterations of ethylene signaling may offer new functions and shift the niche of the holobiont
Altering ethylene levels might allow plants to exploit new niche space, where other trait combinations are optimal. Co-evolution leading to ethylene overproduction (Fig. 3c) and insensitivity (Fig. 3d) might also shift plant niches, as well as restrict the chances for a plant to re-inhabit its ancestral range.
Change in plant-encoded ethylene signaling genes
During co-evolution, some microorganisms are potentially part of holobiont-level ethylene-regulated traits (Fig. 3e, f). This association might reduce some parts of the plant genome working in parallel with the microbiota, saving the cost of gene expression and maintenance of redundant genes. In addition to losing some part of the ethylene signaling pathway, based on the amount of plant dependency on associated microbes, dispersal of seeds to new environments with completely different microbial communities might cause them to die before they are able to adapt to the new conditions and pass the traits down to their offspring.
Uncoupling plant phenotype from mutations in the plant genome
Mutations can alter plant evolution by affecting different pathways including the ethylene pathway. Mutations in the plant ethylene biosynthesis and signaling pathway (for instance, the ability to overproduce ethylene) could cause new morphological traits or functions that promote plant fitness in a new environment, and therefore increase the chances for natural selection. Associated microbiota influence this selection by making the ancestral microbe-associated plants more successful in competition, thereby decreasing the advantage of mutations, as microbes might override the plant-bacteria co-evolution by altering different parts of the ethylene pathway.
The plant hormone ethylene mediates many aspects of plant life history. At the holobiont level, ethylene signaling is a regulatory cascade composed of both plant- and microbiota-associated traits, which together provide a dynamic and fine-tuned response to environmental conditions and stressors. The holobiont perspective in plant hormone regulation also has large evolutionary implications in which plants have become dependent on their microbiome for fully adaptive ethylene-mediated responses. From an agricultural perspective, the plant holobiont may facilitate appropriate or maladapted stress responses depending on the match or mismatch of plant and microbiome traits. Many aspects of plant health related to the microbiome and ethylene signaling may represent a useful model case to further our general understanding of plant holobiont ecology and evolution.
Availability of data and materials
MR and AJ wrote the first draft of the paper. All authors provided and critically reviewed the content. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Consent for publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- Bohnert H, Nelson D, Jensen R. Adaptations to environmental stresses. Plant Cell. 1995;7:1099–111.View ArticlePubMedPubMed CentralGoogle Scholar
- Huot B, Yao J, Montgomery BL, He SY. Growth–defense tradeoffs in plants: a balancing act to optimize fitness. Mol Plant. 2014;7:1267–87.View ArticlePubMedPubMed CentralGoogle Scholar
- Denison RF. Evolutionary tradeoffs as opportunities to improve yield potential. Field Crops Res. 2015;182:3–8.View ArticleGoogle Scholar
- Melotto M, Underwood W, Koczan J, Nomura K, He SY. Plant stomata function in innate immunity against bacterial invasion. Cell. 2006;126:969–80.View ArticlePubMedGoogle Scholar
- Araújo WL, Fernie AR, Nunes-Nesi A. Control of stomatal aperture. Plant Signal Behav. 2011;6:1305–11.View ArticlePubMedPubMed CentralGoogle Scholar
- Leon-Reyes A, Spoel SH, Lange ESD, Abe H, Kobayashi M, Tsuda S, et al. Ethylene modulates the role of NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 in cross talk between salicylate and Jasmonate signaling. Plant Physiol. 2009;149:1797–809.View ArticlePubMedPubMed CentralGoogle Scholar
- Vandenkoornhuyse P, Quaiser A, Duhamel M, Le Van A, Dufresne A. The importance of the microbiome of the plant holobiont. New Phytol. 2015;206:1196–206.View ArticlePubMedGoogle Scholar
- Bleecker AB, Kende H. Ethylene: a gaseous signal molecule in plants [Internet]. https://doi.org/10.1146/annurev.cellbio.16.1.1. 2003 [cited 2017 Mar 27]. Available from: http://annualreviews.org/doi/abs/10.1146/annurev.cellbio.16.1.1.
- Sasidharan R, Voesenek LACJ. Ethylene-mediated acclimations to flooding stress. Plant Physiol. 2015;169:3–12.View ArticlePubMedPubMed CentralGoogle Scholar
- Thao NP, Khan MIR, Thu NBA, Hoang XLT, Asgher M, Khan NA, et al. Role of ethylene and its cross talk with other signaling molecules in plant responses to heavy metal stress. Plant Physiol. 2015;169:73–84.View ArticlePubMedPubMed CentralGoogle Scholar
- Pieterse CMJ, Leon-Reyes A, Van der Ent S, Van Wees SCM. Networking by small-molecule hormones in plant immunity. Nat Chem Biol. 2009;5:308–16.View ArticlePubMedGoogle Scholar
- Scarpeci TE, Frea VS, Zanor MI, Valle EM. Overexpression of AtERF019 delays plant growth and senescence, and improves drought tolerance in Arabidopsis. J Exp Bot. 2017;68:673–85.PubMedGoogle Scholar
- Roux F, Touzet P, Cuguen J, Le Corre V. How to be early flowering: an evolutionary perspective. Trends Plant Sci. 2006;11:375–81.View ArticlePubMedGoogle Scholar
- Schellingen K, Van Der Straeten D, Vandenbussche F, Prinsen E, Remans T, Vangronsveld J, et al. Cadmium-induced ethylene production and responses in Arabidopsis thaliana rely on ACS2 and ACS6 gene expression. BMC Plant Biol. 2014;14:214.View ArticlePubMedPubMed CentralGoogle Scholar
- Barry CS, Blume B, Bouzayen M, Cooper W, Hamilton AJ, Grierson D. Differential expression of the 1-aminocyclopropane-1-carboxylate oxidase gene family of tomato. Plant J. 1996;9:525–35.View ArticlePubMedGoogle Scholar
- Johnson PR, Ecker JR. The ethylene gas signal transduction pathway: a molecular perspective. Annu Rev Genet. 1998;32:227–54.View ArticlePubMedGoogle Scholar
- Alonso JM, Hirayama T, Roman G, Nourizadeh S, Ecker JR. EIN2, a bifunctional transducer of ethylene and stress responses in Arabidopsis. Science. 1999;284:2148–52.View ArticlePubMedGoogle Scholar
- An F, Zhao Q, Ji Y, Li W, Jiang Z, Yu X, et al. Ethylene-induced stabilization of ETHYLENE INSENSITIVE3 and EIN3-LIKE1 is mediated by proteasomal degradation of EIN3 binding F-box 1 and 2 that requires EIN2 in Arabidopsis. Plant Cell Online. 2010;22:2384–401.View ArticleGoogle Scholar
- Groen SC, Whiteman NK, Bahrami AK, Wilczek AM, Cui J, Russell JA, et al. Pathogen-triggered ethylene signaling mediates systemic-induced susceptibility to herbivory in Arabidopsis. Plant Cell Online. 2013;25:4755–66.View ArticleGoogle Scholar
- Kacperska A. Ethylene synthesis and a role in plant responses to different stressors. Biol Biotechnol Plant Horm Ethyl [Internet]. Springer, Dordrecht; 1997 [cited 2017 Oct 12]. p. 207–16. Available from: https://0-link-springer-com.brum.beds.ac.uk/chapter/10.1007/978-94-011-5546-5_27.
- Wees SCMV, Pelt JAV, Bakker PAHM, Pieterse CMJ. Bioassays for assessing Jasmonate-dependent defenses triggered by pathogens, herbivorous insects, or beneficial rhizobacteria. Jasmonate Signal [Internet]. Humana Press, Totowa, NJ; 2013 [cited 2017 Oct 3]. p. 35–49. Available from: https://0-link-springer-com.brum.beds.ac.uk/protocol/10.1007/978-1-62703-414-2_4.
- van Loon LC, Rep M, Pieterse CMJ. Significance of inducible defense-related proteins in infected plants. Annu Rev Phytopathol. 2006;44:135–62.View ArticlePubMedGoogle Scholar
- Morgan PW, Drew MC. Ethylene and plant responses to stress. Physiol Plant. 1997;100:620–30.View ArticleGoogle Scholar
- Peng J, Li Z, Wen X, Li W, Shi H, Yang L, et al. Salt-induced stabilization of EIN3/EIL1 confers salinity tolerance by deterring ROS accumulation in Arabidopsis. PLoS Genet. 2014;10:e1004664.View ArticlePubMedPubMed CentralGoogle Scholar
- Keunen E, Schellingen K, Vangronsveld J, Cuypers A. Ethylene and metal stress: small molecule, big impact. Front Plant Sci [Internet]. 2016 [cited 2017 Feb 22];7. Available from: http://0-www.ncbi.nlm.nih.gov.brum.beds.ac.uk/pmc/articles/PMC4735362/.
- Tao J-J, Chen H-W, Ma B, Zhang W-K, Chen S-Y, Zhang J-S. The role of ethylene in plants under salinity stress. Front Plant Sci [Internet]. 2015 [cited 2017 Feb 24];6. Available from: http://journal.frontiersin.org/article/10.3389/fpls.2015.01059/.
- Vassilev A, Lidon F, Scotti P, Graca MD, Yordanov I. Cadmium-induced changes in chloroplast lipids and photosystem activities in barley plants. Biol Plant. 2004;48:153–6.View ArticleGoogle Scholar
- Berumen S, Lownds NK. Ethylene production as a drought stress response in Cassia corymbosa. Hortscience. 1996;31:649.Google Scholar
- Remans T, Thijs S, Truyens S, Weyens N, Schellingen K, Keunen E, et al. Understanding the development of roots exposed to contaminants and the potential of plant-associated bacteria for optimization of growth. Ann Bot. 2012;110:239–52.View ArticlePubMedPubMed CentralGoogle Scholar
- Wilkinson S, Davies WJ. Drought, ozone, ABA and ethylene: new insights from cell to plant to community. Plant Cell Environ. 2010;33:510–25.View ArticlePubMedGoogle Scholar
- Bailey-Serres J, Voesenek LACJ. Flooding stress: acclimations and genetic diversity. Annu Rev Plant Biol. 2008;59:313–39.View ArticlePubMedGoogle Scholar
- Street IH, Schaller GE. Ethylene: a gaseous signal in plants and bacteria. Biochem(Lond). 2016;38:4–7.Google Scholar
- Voesenek LACJ, Pierik R, Sasidharan R. Plant life without ethylene. Trends Plant Sci. 2015;20:783–6.View ArticlePubMedGoogle Scholar
- Fan Q-J, Liu J-H. Colonization with arbuscular mycorrhizal fungus affects growth, drought tolerance and expression of stress-responsive genes in Poncirus trifoliata. Acta Physiol Plant. 2011;33:1533.View ArticleGoogle Scholar
- Lasserre E, Bouquin T, Hernandez JA, Pech J-C, Balagué C, Bull J. Structure and expression of three genes encoding ACC oxidase homologs from melon (Cucumis melo L.). Mol Gen Genet MGG. 1996;251:81–90.PubMedGoogle Scholar
- Peng H-P, Lin T-Y, Wang N-N, Shih M-C. Differential expression of genes encoding 1-aminocyclopropane-1-carboxylate synthase in Arabidopsis during hypoxia. Plant Mol Biol. 2005;58:15–25.View ArticlePubMedGoogle Scholar
- Li T, Tan D, Yang X, Wang A. Exploring the apple genome reveals six ACC synthase genes expressed during fruit ripening. Sci Hortic. 2013;157:119–23.View ArticleGoogle Scholar
- Vogel JP, Woeste KE, Theologis A, Kieber JJ. Recessive and dominant mutations in the ethylene biosynthetic gene ACS5 of Arabidopsis confer cytokinin insensitivity and ethylene overproduction, respectively. Proc Natl Acad Sci. 1998;95:4766–71.View ArticlePubMedPubMed CentralGoogle Scholar
- Young TE, Meeley RB, Gallie DR. ACC synthase expression regulates leaf performance and drought tolerance in maize. Plant J. 2004;40:813–25.View ArticlePubMedGoogle Scholar
- Dal Cin V, Rizzini FM, Botton A, Tonutti P. The ethylene biosynthetic and signal transduction pathways are differently affected by 1-MCP in apple and peach fruit. Postharvest Biol Technol. 2006;42:125–33.View ArticleGoogle Scholar
- Yang C, Ma B, He S-J, Xiong Q, Duan K-X, Yin C-C, et al. MHZ6/OsEIL1 and OsEIL2 regulate ethylene response of roots and coleoptiles and negatively affect salt tolerance in rice. Plant Physiol. 2015;169:148. pp.00353.2015View ArticlePubMedPubMed CentralGoogle Scholar
- Pierik R, Sasidharan R, Voesenek LACJ. Growth control by ethylene: adjusting phenotypes to the environment. J Plant Growth Regul. 2007;26:188–200.View ArticleGoogle Scholar
- Dugardeyn J, Van Der Straeten D. Ethylene: fine-tuning plant growth and development by stimulation and inhibition of elongation. Plant Sci. 2008;175:59–70.View ArticleGoogle Scholar
- Zilber-Rosenberg I, Rosenberg E. Role of microorganisms in the evolution of animals and plants: the hologenome theory of evolution. FEMS Microbiol Rev. 2008;32:723–35.View ArticlePubMedGoogle Scholar
- Berendsen RL, Pieterse CMJ, Bakker PAHM. The rhizosphere microbiome and plant health. Trends Plant Sci. 2012;17:478–86.View ArticlePubMedGoogle Scholar
- Ruíz-Sánchez M, Armada E, Muñoz Y, García de Salamone IE, Aroca R, Ruíz-Lozano JM, et al. Azospirillum and arbuscular mycorrhizal colonization enhance rice growth and physiological traits under well-watered and drought conditions. J Plant Physiol. 2011;168:1031–7.View ArticlePubMedGoogle Scholar
- Horvath RS. Microbial co-metabolism and the degradation of organic compounds in nature. Bacteriol Rev. 1972;36:146–55.PubMedPubMed CentralGoogle Scholar
- Lloyd JR, Lovley DR. Microbial detoxification of metals and radionuclides. Curr Opin Biotechnol. 2001;12:248–53.View ArticlePubMedGoogle Scholar
- Suganuma N, Yamauchi H, Yamamoto K. Enhanced production of ethylene by soybean roots after inoculation with Bradyrhizobium japonicum. Plant Sci. 1995;111:163–8.View ArticleGoogle Scholar
- Weingart H, Volksch B. Ethylene production by Pseudomonas syringae pathovars in vitro and in planta. Appl Environ Microbiol. 1997;63:156–61.PubMedPubMed CentralGoogle Scholar
- Fukuda H, Ogawa T, Tanase S. Ethylene production by micro-organisms. In: Rose AH, editor. Adv Microb Physiol [Internet]. Academic Press; 1993 [cited 2017 Sep 28]. p. 275–306. Available from: http://0-www.sciencedirect.com.brum.beds.ac.uk/science/article/pii/S0065291108601010
- Freebairn HT, Buddenhagen IW. Ethylene production by Pseudomonas solanacearum. Nature. 1964;202:313–4.View ArticlePubMedGoogle Scholar
- Nagahama K, Ogawa T, Fujii T, Fukuda H. Classification of ethylene-producing bacteria in terms of biosynthetic pathways to ethylene. J Ferment Bioeng. 1992;73:1–5.View ArticleGoogle Scholar
- Eckert C, Xu W, Xiong W, Lynch S, Ungerer J, Tao L, et al. Ethylene-forming enzyme and bioethylene production. Biotechnol Biofuels. 2014;7:33.View ArticlePubMedPubMed CentralGoogle Scholar
- Sato M, Watanabe K, Yazawa M, Takikawa Y, Nishiyama K. Detection of new ethylene-producing bacteria, Pseudomonas syringae pvs. cannabina and sesami, by PCR amplification of genes for the ethylene-forming enzyme. Phytopathology. 1997;87:1192–6.View ArticlePubMedGoogle Scholar
- Jäckel U, Schnell S, Conrad R. Microbial ethylene production and inhibition of methanotrophic activity in a deciduous forest soil. Soil Biol Biochem. 2004;36:835–40.Google Scholar
- Digiacomo F, Girelli G, Aor B, Marchioretti C, Pedrotti M, Perli T, et al. Ethylene-producing bacteria that ripen fruit. ACS Synth Biol. 2014;3:935–8.View ArticlePubMedGoogle Scholar
- Veselov D, Langhans M, Hartung W, Aloni R, Feussner I, Götz C, et al. Development of Agrobacterium tumefaciens C58-induced plant tumors and impact on host shoots are controlled by a cascade of jasmonic acid, auxin, cytokinin, ethylene and abscisic acid. Planta. 2003;216:512–22.PubMedGoogle Scholar
- Patten CL, Glick BR. Role of Pseudomonas putida indoleacetic acid in development of the host plant root system. Appl Environ Microbiol. 2002;68:3795–801.View ArticlePubMedPubMed CentralGoogle Scholar
- Vogel JP, Schuerman P, Woeste K, Brandstatter I, Kieber JJ. Isolation and characterization of Arabidopsis mutants defective in the induction of ethylene biosynthesis by cytokinin. Genetics. 1998;149:417–27.PubMedPubMed CentralGoogle Scholar
- Yeong-Biau Y, Shang Fa Y. Auxin-induced ethylene production and its inhibition by aminoethyoxyvinylglycine and cobalt ion|Plant Physiology [Internet]. [cited 2017 Oct 12]. Available from: http://www.plantphysiol.org/content/64/6/1074.
- Lorteau M-A, Ferguson BJ, Guinel FC. Effects of cytokinin on ethylene production and nodulation in pea (Pisumsativum) cv. Sparkle Physiol Plant. 2001;112:421–8.View ArticlePubMedGoogle Scholar
- Glick BR. Bacteria with ACC deaminase can promote plant growth and help to feed the world. Microbiol Res. 2014;169:30–9.View ArticlePubMedGoogle Scholar
- Singh RP, Shelke GM, Kumar A, Jha PN. Biochemistry and genetics of ACC deaminase: a weapon to “stress ethylene” produced in plants. Front Microbiol [Internet]. 2015 [cited 2017 Mar 27];6. Available from: http://journal.frontiersin.org/article/10.3389/fmicb.2015.00937/abstract.
- Nascimento FX, Rossi MJ, Soares CRFS, McConkey BJ, Glick BR. New insights into 1-aminocyclopropane-1-carboxylate (ACC) deaminase phylogeny. Evolution and Ecological Significance PLOS ONE. 2014;9:e99168.View ArticlePubMedGoogle Scholar
- Blaha D, Prigent-Combaret C, Mirza MS, Moënne-Loccoz Y. Phylogeny of the 1-aminocyclopropane-1-carboxylic acid deaminase-encoding gene acdS in phytobeneficial and pathogenic Proteobacteria and relation with strain biogeography. FEMS Microbiol Ecol. 2006;56:455–70.View ArticlePubMedGoogle Scholar
- Hontzeas N, Richardson AO, Belimov A, Safronova V, Abu-Omar MM, Glick BR. Evidence for horizontal transfer of 1-aminocyclopropane-1-carboxylate deaminase genes. Appl Environ Microbiol. 2005;71:7556–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Ravanbakhsh M, Sasidharan R, Voesenek LACJ, Kowalchuk GA, Jousset A. ACC deaminase-producing rhizosphere bacteria modulate plant responses to flooding. J Ecol. 2017;105:979.Google Scholar
- Hall JA, Peirson D, Ghosh S, Glick BR. Root elongation in various agronomic crops by the plant growth promoting rhizobacterium Pseudomonas putida Gr12–2. Isr J Plant Sci. 1996;44:37–42.View ArticleGoogle Scholar
- Vacheron J, Combes-Meynet E, Walker V, Gouesnard B, Muller D, Moënne-Loccoz Y, et al. Expression on roots and contribution to maize phytostimulation of 1-aminocyclopropane-1-decarboxylate deaminase gene acdS in Pseudomonas fluorescens F113. Plant Soil. 2016;407:187–202.View ArticleGoogle Scholar
- Desbrosses G, Contesto C, Varoquaux F, Galland M, Touraine B. PGPR-Arabidopsis interactions is a useful system to study signaling pathways involved in plant developmental control. Plant Signal Behav. 2009;4:319–21.View ArticleGoogle Scholar
- Koevoets IT, Venema JH, Elzenga JTM, Testerink C. Roots withstanding their environment: exploiting root system architecture responses to abiotic stress to improve crop tolerance. Front Plant Sci [Internet]. 2016 [cited 2018 Jan 26];7. Available from: https://0-www-ncbi-nlm-nih-gov.brum.beds.ac.uk/pmc/articles/PMC5005332/.
- Carlos M-HJ, Stefani P-VY, Janette A-M, Melani M-SS, Gabriela P-O. Assessing the effects of heavy metals in ACC deaminase and IAA production on plant growth-promoting bacteria. Microbiol Res. 2016;188:53–61.View ArticlePubMedGoogle Scholar
- Golicz AA, Schliep M, Lee HT, Larkum AWD, Dolferus R, Batley J, et al. Genome-wide survey of the seagrass Zostera muelleri suggests modification of the ethylene signalling network. J Exp Bot. 2015;66:1489–98.View ArticlePubMedPubMed CentralGoogle Scholar
- Osborne DJ, Walters J, Milborrow BV, Norville A, Stange LMC. Special publication evidence for a non-ACC ethylene biosynthesis pathway in lower plants. Phytochemistry. 1996;42:51–60.View ArticleGoogle Scholar
- Groen SC, Whiteman NK. The evolution of ethylene signaling in plant chemical ecology. J Chem Ecol. 2014;40:700–16.View ArticlePubMedGoogle Scholar
- Campbell R, Greaves MP. Anatomy and community structure of the rhizosphere. In: Lynch JM, editor. The rhizosphere. Chichester, England: Wiley 1990:11–34.Google Scholar
- Duan J, Müller KM, Charles TC, Vesely S, Glick BR. 1-Aminocyclopropane-1-carboxylate (ACC) deaminase genes in rhizobia from Southern Saskatchewan. Microb Ecol. 2009;57:423–36.View ArticlePubMedGoogle Scholar
- Smith AM, Cook RJ. Implications of ethylene production by bacteria for biological balance of soil. Nature. 1974;252:703–5.Google Scholar
- Rosenberg E, Zilber-Rosenberg I. Microbes drive evolution of animals and plants: the Hologenome concept. MBio. 2016;7:e01395–15.View ArticlePubMedPubMed CentralGoogle Scholar
- Nascimento FX, Brígido C, Glick BR, Oliveira S. ACC deaminase genes are conserved among Mesorhizobium species able to nodulate the same host plant. FEMS Microbiol Lett. 2012;336:26–37.View ArticlePubMedGoogle Scholar
- van Veen H, Mustroph A, Barding GA, Eijk MV, Welschen-Evertman RAM, Pedersen O, et al. Two Rumex species from contrasting hydrological niches regulate flooding tolerance through distinct mechanisms. Plant Cell Online. 2013;25:4691–707.View ArticleGoogle Scholar
- Guan R, Su J, Meng X, Li S, Li Y, Xu J, et al. Multi-layered regulation of ethylene induction plays a positive role in Arabidopsis resistance against Pseudomonas syringae. Plant Physiol. 2015;169:299–312.Google Scholar
- Arteca RN, Arteca JM. Effects of brassinosteroid, auxin, and cytokinin on ethylene production in Arabidopsis thaliana plants. J Exp Bot. 2008;59:3019–26.View ArticlePubMedPubMed CentralGoogle Scholar