Ethylene Sensitivity Research Articles

Good intentions, bad outcomes: Impact of mixed-fruit loading on banana fruit protein expression, physiological responses and quality

Mixed-fruit storage and/or transport could have detrimental impact on quality, due to varying ethylene sensitivities. This study evaluated the effects of mixed-fruit loading on physicochemical and physiological changes as well as protein expression of bananas during storage. Bananas, apples (Smartfresh™-treated), and pears were stored together (simulating mixed-fruit loading) and individually (control) at 15 °C for 9 days. Post-storage ethylene production rates were significantly higher (p ≤ 0.05) for fruit under mixed-fruit loading. Bananas from mixed-fruit had higher respiration rate (44.4 ± 8.83 mL/kg h) compared to control on day 9. Chroma values increased, while hue angle declined significantly for bananas across all treatments during storage (p ≤ 0.05). One-dimensional sodium dodecyl sulphate-polyacrylamide (SDS-PAGE) gel electrophoresis for protein extracted from banana peels confirmed overexpression of proteins within 25−37 kDa on day 9. Results obtained emphasize the need for correct management of fruit based on ethylene sensitivity in order to extend shelf life.

TREE1-EIN3–mediated transcriptional repression inhibits shoot growth in response to ethylene

Ethylene is an important plant hormone that regulates plant growth, in which the master transcriptionactivator EIN3 (Ethylene Insensitive 3)-mediated transcriptional activation plays vital roles. However, the EIN3-mediated transcriptional repression in ethylene response is unknown. We report here that a Transcriptional Repressor of EIN3-dependent Ethylene-response 1 (TREE1) interacts with EIN3 to regulate transcriptional repression that leads to an inhibition of shoot growth in response to ethylene. Tissue-specific transcriptome analysis showed that most of the genes are down-regulated by ethylene in shoots, and a DNA binding motif was identified that is important for this transcriptional repression. TREE1 binds to the DNA motif to repress gene expression in an EIN3-dependent manner. Genetic validation demonstrated that repression of TREE1-targeted genes leads to an inhibition of shoot growth. Overall, this work establishes a mechanism by which transcriptional repressor TREE1 interacts with EIN3 to inhibit shoot growth via transcriptional repression in response to ethylene.

Ethylene-independent functions of the ethylene precursor ACC in Marchantia polymorpha.

The plant hormone ethylene has many roles in growth and development1. In seed plants, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is converted into ethylene by ACC oxidase (ACO), and treatment with ACC induces ethylene responses2. However, non-seed plants lack ACO homologues3-8, which led us to examine the relationship between ACC and ethylene in the liverwort Marchantia polymorpha. Here, we demonstrate that ACC and ethylene can induce divergent growth responses in Marchantia. Ethylene increases plant and gemma size, induces more gemma cups and promotes gemmae dormancy. As predicted, Mpctr1-knockout mutants display constitutive ethylene responses, whereas Mpein3-knockout mutants exhibit ethylene insensitivity. Compared with the wild type, Mpctr1 gemmae have more and larger epidermal cells, whereas Mpein3 gemmae have fewer and smaller epidermal cells, suggesting that ethylene promotes cell division and growth in developing gemmae. By contrast, ACC treatment inhibits gemma growth and development by suppressing cell division, even in the Mpein3-knockout alleles. Knockout mutants of one or both ACC SYNTHASE (ACS) gene homologues produce negligible levels of ACC, have more and larger gemma cups, and have more-expanded thallus branches. Mpacs2 and Mpacs1 Mpacs2 gemmae also display a high frequency of abnormal apical notches (meristems) that are not observed in ethylene mutants. These findings reveal that ethylene and ACC have distinct functions, and suggest that ACC is a signalling molecule in Marchantia. ACC may be an evolutionarily conserved signal that predates its efficient conversion to ethylene in higher plants.

Physiological and metabolic bases of increased growth in the tomato ethylene-insensitive mutant Never ripe: extending ethylene signaling functions.

The tomato mutant Never ripe(Nr), a loss-of-function for the ethylene receptor SlETR3, shows enhanced growth, associated with increased carbon assimilation and a rewiring of the central metabolism. Compelling evidence has demonstrated the importance of ethylene during tomato fruit development, yet its role on leaf central metabolism and plant growth remains elusive. Here, we performed a detailed characterization of Never ripe (Nr) tomato, a loss-of-function mutant for the ethylene receptor SlETR3, known for its fruits which never ripe. However, besides fruits, the Nr gene is also constitutively expressed in vegetative tissues. Nr mutant showed a growth enhancement during both the vegetative and reproductive stage, without an earlier onset of leaf senescence, with Nr plants exhibiting a higher number of leaves and an increased dry weight of leaves, stems, roots, and fruits. At metabolic level, Nr also plays a significant role with the mutant showing changes in carbon assimilation, carbohydrates turnover, and an exquisite reprogramming of a large number of metabolite levels. Notably, the expression of genes related to ethylene signaling and biosynthesis are not altered in Nr. We assess our results in the context of those previously published for tomato fruits and of current models of ethylene signal transduction, and conclude that ethylene insensitivity mediated by Nr impacts the whole central metabolism at vegetative stage, leading to increased growth rates.

Petal abscission in fragrant roses is associated with large scale differential regulation of the abscission zone transcriptome

Flowers of fragrant roses such as Rosa bourboniana are ethylene-sensitive and undergo rapid petal abscission while hybrid roses show reduced ethylene sensitivity and delayed abscission. To understand the molecular mechanism underlying these differences, a comparative transcriptome of petal abscission zones (AZ) of 0 h and 8 h ethylene-treated flowers from R. bourboniana was performed. Differential regulation of 3700 genes (1518 up, 2182 down) representing 8.5% of the AZ transcriptome was observed between 0 and 8 h ethylene-treated R. bourboniana petal AZ. Abscission was associated with large scale up-regulation of the ethylene pathway but prominent suppression of the JA, auxin and light-regulated pathways. Regulatory genes encoding kinases/phosphatases/F-box proteins and transcription factors formed the major group undergoing differential regulation besides genes for transporters, wall modification, defense and phenylpropanoid pathways. Further comparisons with ethylene-treated petals of R. bourboniana and 8 h ethylene-treated AZ (R. hybrida) identified a core set of 255 genes uniquely regulated by ethylene in R. bourboniana AZ. Almost 23% of these encoded regulatory proteins largely conserved with Arabidopsis AZ components. Most of these were up-regulated while an entire set of photosystem genes was prominently down-regulated. The studies provide important information on regulation of petal abscission in roses.

UV RESISTANCE LOCUS8 mediates ultraviolet-B-induced stomatal closure in an ethylene-dependent manner

Although the UV RESISTANCE LOCUS 8 (UVR8)-CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)-ELONGATED HYPOCOTYL5 (HY5) signaling pathway, ethylene, hydrogen peroxide (H2O2), and nitric oxide (NO) all participate in ultraviolet-B (UV-B)-triggered stomatal closing, their interrelationship is not clear. Here, we found that UV-B-induced the expression of ethylene biosynthetic genes, production of ethylene, H2O2, and NO, and stomata closing were impaired in uvr8, cop1, and hy5 mutants. UV-B-induced NO production and stomata closing were also defective in mutants for ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), and EIN3, but UV-B-triggered H2O2 generation was only inhibited in etr1. In either the absence or presence of UV-B, ethylene triggered H2O2 production but not NO generation and stomatal closure in cop1 and hy5, and stomata closing in cop1 and hy5 was induced by NO but not H2O2. Moreover, NO production and stomatal closure were constitutively caused by over-expression of COP1 or HY5 in ein2 and ein3, but not by over-expression of EIN2 or EIN3 in cop1 and hy5. Our data indicate that the UVR8-COP1-HY5 signaling module mediates UV-B-induced ethylene production, ethylene is then perceived by ETR1 to induce H2O2 synthesis. H2O2 induces NO generation and subsequent stomata closing via an EIN2, EIN3, COP1, and HY5-dependent pathway(s).

Changes in physiological and photosynthetic parameters in tomato of different ethylene status under salt stress: Effects of exogenous 1-aminocyclopropane-1-carboxylic acid treatment and the inhibition of ethylene signalling

Although ethylene (ET) is an important participant in plant responses to salt stress, its role in the early period of acclimation, especially in the case of photosynthesis has not been revealed in detail. In this study, the effects of tolerable (100 mM) or lethal (250 mM) NaCl concentrations were investigated in hydroponically grown tomato (Solanum lycopersicum L. cv. Ailsa Craig) plants of different ET status, in wild type (WT) plants, in WT plants pre-treated with the ET generator 1-aminocyclopropane-1-carboxylic acid (ACC) and in ET insensitive, Never ripe (Nr/Nr) mutants for 1-, 6- and 24 h. In the leaves ACC treatment reduced the osmotic effect of salt stress, while Nr mutation enhanced not only osmotic but ionic component of salt stress at 100 mM NaCl. ET insensitivity caused greater decline in stomatal conductance and photosynthetic CO2 assimilation rate than in the controls under tolerable salt stress, but both ACC treatment and Nr mutation helped to maintain positive carbon assimilation under lethal salt stress after 24 h. Nr mutant leaves showed highly enhanced regulated non-photochemical quenching (NPQ) and therefore lower quantum yield of photosystem II (PSII), due to more intensive cyclic electron flow around photosystem I (CEF-PSI), which was further increased under high salinity. Exogenous ACC treatment lowered CEF-PSI and enhanced PSII photochemistry after 6 h of lethal salt stress. Controlling PSI photoinhibition, ET is suggested to be an important regulator of CEF-PSI and photoprotection under salt stress. Furthermore, the altered ET status could cause contrasting effects under different stress severity.

Ethylene Exposure Exacerbates Botrytis Damage in Cut Roses1

AbstractSeparate experiments showed that current cut rose (Rosa × hybrida) cultivars vary considerably in Botrytis (Botrytis cinerea) susceptibility and ethylene (ET) sensitivity. There was no pattern when considering these two traits together for the 26 cultivars used, and neither trait appeared predictive of the other. Four cultivars were identified that included one each that is Botrytis susceptible/ET sensitive, Botrytis non-susceptible/ET sensitive, Botrytis susceptible/ET insensitive, and Botrytis non-susceptible/ET insensitive. Exposing these cultivars to ET often resulted in reduced vase life and more pronounced negative Botrytis responses (flower Botrytis damage, leaf Botrytis incidence, and frequency of termination due to Botrytis). This was true for ET sensitive and insensitive cultivars, Botrytis susceptible and non-susceptible cultivars, Botrytis inoculated and non-inoculated stems, and stems exposed to ET either before or after Botrytis inoculation and incubation. Thus, even if ET is not thought to have a major influence on a given cut rose cultivar in terms of classic negative ET responses (leaf drop, petal wilt, altered opening rate), ET exposure could have a significant negative impact on that cultivar by exacerbating Botrytis damage. Shipping temperatures and methods can have a strong influence on Botrytis damage, with pre-cooling of shipping boxes before cold storage/transport being beneficial.Index words: Botrytis blight, Botrytis cinerea, cut flowers, floriculture, gray mold, Rosa L. hybrids.Species used in this study: Rose (Rosa × hybrida) focal cultivars ‘Cuenca', ‘Daphnee', ‘Freedom', ‘Vendela'; Botrytis (Botrytis cinerea Pers. ex. Fr.).Chemicals used in this study: 1-methylcyclopropene (EthylBloc); ethylene; silver thiosulfate.

Cytosolic Invertase-Mediated Root Growth Is Feedback Regulated by a Glucose-Dependent Signaling Loop.

The disaccharide Suc cannot be utilized directly; rather, it is irreversibly hydrolyzed by invertase to the hexoses Glc and Fru to shape plant growth. In this context, Glc controls the stability of the transcription factor Ethylene-Insensitive3 (EIN3) via the function of Hexokinase1 (HXK1), a Glc sensor. Thus, invertase, especially the major neutral cytosolic invertase (CINV), constitutes a key point of control for plant growth. However, the cognate regulatory mechanisms that modulate CINV activity remain unclear. Here, we demonstrate that in Arabidopsis (Arabidopsis thaliana), EIN3 binds directly to both the promoters of Production of Anthocyanin Pigment1 (PAP1) and Phosphatidylinositol Monophosphate 5-Kinase 9 (PIP5K9), repressing and enhancing, respectively, their expression. Subsequently, PAP1 binds directly to and promotes transcription of the Cytosolic Invertase1 (CINV1) promoter, while PIP5K9 interacts with and negatively regulates CINV1. The accumulated CINV1 subsequently hydrolyzes Suc, releasing the sequestered signaling cue, Glc, which has been shown to negatively regulate the stability of EIN3 via HXK1. We conclude that a CINV1-Glc-HXK1-EIN3-PAP1/PIP5K9-CINV1 loop contributes to the modulation of CINV1 activity regulating root growth by Glc signaling.

Yellow-fruited phenotype is caused by 573 bp insertion at 5' UTR of YFT1 allele in yft1 mutant tomato

The yft1 tomato mutant has a yellow-fruited phenotype controlled by a recessive gene of YFT1 allele, which has been shown by map-based cloning to be a homolog of ETHYLENE INSENSITIVE 2 (EIN2). Genetic lesion of YFT1 allele in yft1 is attributed to a 573 bp DNA fragment (IF573) insertion at 1,200 bp downstream of the transcription start site. Transcriptomic analysis revealed that YFT1 lesion resulted in 5,053 differentially expressed genes (DEGs) in yft1 pericarp compared with the M82 wild type cultivar. These were annotated as being involved in ethylene synthesis, chromoplast development, and carotenoid synthesis. The YFT1 lesion caused a reduction in its own transcript levels in yft1 and impaired ethylene emission and signal transduction, delayed chromoplast development and decreased carotenoid accumulation. The molecular mechanism underlying the downregulated YFT1 allele in yft1 was examined at both RNA and DNA levels. The IF573 event appeared to introduce two negative regulatory sequences located at -272 to -173 bp and -172 to -73 bp in the YFT1 allele promoter, causing alterative splicing due to introduction of aberrant splicing sites, and breaking upstream open reading frames (uORF) structure in the 5'-UTR. Those results a new provided insight into molecular regulation of color formation in tomato fruit.

The basic helix-loop-helix transcription factor bHLH95 affects fruit ripening and multiple metabolisms in tomato.

Ethylene signaling pathways regulate several physiological alterations that occur during tomato fruit ripening, such as changes in colour and flavour. The mechanisms underlying the transcriptional regulation of genes in these pathways remain unclear, although the role of the MADS-box transcription factor RIN has been widely reported. Here, we describe a bHLH transcription factor, SlbHLH95, whose transcripts accumulated abundantly in breaker+4 and breaker+7 fruits compared with rin (ripening inhibitor) and Nr (never ripe) mutants. Moreover, the promoter activity of SlbHLH95 was regulated by RIN in vivo. Suppression of SlbHLH95 resulted in reduced sensitivity to ethylene, decreased accumulation of total carotenoids, and lowered glutathione content, and inhibited the expression of fruit ripening- and glutathione metabolism-related genes. Conversely, up-regulation of SlbHLH95 in wild-type tomato resulted in higher sensitivity to ethylene, increased accumulation of total carotenoids, slightly premature ripening, and elevated accumulation of glutathione, soluble sugar, and starch. Notably, overexpression of SlbHLH95 in rin led to the up-regulated expression of fruit ripening-related genes (FUL1, FUL2, SAUR69, ERF4, and CNR) and multiple glutathione metabolism-related genes (GSH1, GSH2, GSTF1, and GSTF5). These results clarified that SlbHLH95 participates in the regulation of fruit ripening and affects ethylene sensitivity and multiple metabolisms targeted by RIN in tomato.

Two androecious mutations reveal the crucial role of ethylene receptors in the initiation of female flower development in Cucurbita pepo.

Ethylene is the key regulator of sex determination in monoecious species of the family Cucurbitaceae. This hormone determines which individual floral meristems develop as female or male flowers and the female flowering transition. The sex determination genes discovered so far code for ethylene biosynthesis enzymes, but little is known about the importance of ethylene signaling components. In this paper we characterize two novel ethylene-insensitive mutations (etr1a-1 and etr1b) which block the female flowering transition of Cucurbita pepo; this makes plants produce male flowers indefinitely (androecy). Two missense mutations in the ethylene-binding domain of the ethylene receptors CpETR1A or CpETR1B were identified as the causal mutations of these phenotypes by using whole-genome resequencing. The distinctive phenotypes of single and double mutants for four etr mutations have demonstrated that the final level of ethylene insensitivity depends upon the strength and dosage of mutant alleles for at least three cooperating ETR genes, and that the level of ethylene insensitivity determines the final sex phenotype of the plant. The sex phenotype ranges from monoecy in ethylene-sensitive wild-type plants to androecy in the strongest ethylene-insensitive ones, via andromonoecy in partially ethylene-insensitive plants. The induction of female flowering transition was found to be associated with upregulation of CpACS11, CpACO2 and CpACS27, three ethylene biosynthesis genes required for female flower development. A model is proposed herein, integrating both ethylene biosynthesis and receptor genes into the genetic network which regulates sex determination in C.pepo.

Maintenance of photosynthetic capacity in flooded tomato plants with reduced ethylene sensitivity.

Ethylene is considered one of the most important plant hormones orchestrating plant responses to flooding stress. However, ethylene may induce deleterious effects on plants, especially when produced at high rates in response to stress. In this paper, we explored the effect of attenuated ethylene sensitivity in the Never ripe (Nr) mutant on leaf photosynthetic capacity of flooded tomato plants. We found out that reduced ethylene perception in Nr plants was associated with a more efficient photochemical and non-photochemical radiative energy dissipation capability in response to flooding. The data correlated with the retention of chlorophyll and carotenoids content in flooded Nr leaves. Moreover, leaf area and specific leaf area were higher in Nr, indicating that ethylene would exert a negative role in leaf growth and expansion under flooded conditions. Although stomatal conductance was hampered in flooded Nr plants, carboxylation activity was not affected by flooding in the mutant, suggesting that ethylene is responsible for inducing non-stomatal limitations to photosynthetic CO2 uptake. Upregulation of several cysteine protease genes and high protease activity led to Rubisco protein loss in response to ethylene under flooding. Reduction of Rubisco content would, at least in part, account for the reduction of its carboxylation efficiency in response to ethylene in flooded plants. Therefore, besides its role as a trigger of many adaptive responses, perception of ethylene entails limitations in light and dark photosynthetic reactions by speeding up the senescence process that leads to a progressive disassembly of the photosynthetic machinery in leaves of flooded tomato plants.

Effects of ethylene biosynthesis and signaling on oxidative stress and antioxidant defense system in Nelumbo nucifera G. under cadmium exposure.

Water contamination with cadmium (Cd) is a global environmental problem and its remediation becomes urgent. Phytoremediation using ornamental plants has attracted much attention for its advantages of cost-effectiveness and beautification of the environment. Nelumbo nucifera G. is a popular ornamental aquatic macrophyte with fast growth, large biomass, and high capacities for Cd accumulation and removal. However, information about Cd resistance and defense responses in N. nucifera is rather scarce, which restricts its large-scale utilization for phytoremediation. The phytohormone ethylene plays an important role in plant resistance to Cd stress, but the underlying mechanism remains unclear. In this study, we investigated morphophysiological responses of N. nucifera seedlings to Cd stress, and focused on the effects of ethylene on oxidative damage, Cd accumulation, and antioxidant defense system at the metabolic and transcript levels in leaves under Cd stress. Our results showed that Cd exposure led to leaf chlorosis and necrosis, coupled with an increase in contents of hydrogen peroxide, electrolyte leakage, and malondialdehyde, and decrease in chlorophyll content. Exogenous ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) application intensified Cd-induced stress responses and Cd accumulation, and increased ethylene production by inducing ACC synthase (ACS) gene NnACS. Such enhanced ethylene emission inhibited catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities, and modulated ascorbate (AsA) and glutathione (GSH) accumulation through transcriptional regulation of their respective metabolic genes. After ethylene action inhibitor silver thiosulfate (STS) supplementation, Cd-induced oxidative damage was abolished, and Cd content declined but still at a relatively high level. Blocking of ethylene perception by STS inhibited ethylene biosynthesis; enhanced CAT, APX, and GR activities and their transcript levels; increased AsA accumulation via inducing its biosynthetic genes; but reduced GSH content and NnGSH2 expression level. These results suggest that ethylene biosynthesis and signaling play an important role in N. nucifera response to Cd stress, and maintaining appropriate ethylene level and low ethylene sensitivity could improve its Cd tolerance via efficient antioxidant defenses.

The Effect of Ethylene on the Color Change and Resistance to Botrytis cinerea Infection in 'Kyoho' Grape Fruits.

The formation of grape quality and the mechanism of resistance against foreign pathogens affect the storage stability of fruits during post-harvest handling. Ethylene plays a crucial role in regulating the ripeness of fruits and can be used as an exogenous regulator to resist exogenous pathogens. In this study, we used different concentrations of ethephon for treatment of grape fruits before veraison, analyzed the anthocyanin content, soluble solids, titratable acid, and determined fruit firmness and cell wall metabolism-related enzymes during fruit development. Results showed that exogenous ethephon promoted the early coloration of grape fruits and increased the coloring-related genes myeloblastosis A1(MYBA1), myeloblastosis A2(MYBA2), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3’-hydroxylase gene (F3’H), flavonoid 3’, 5’hydroxylase (F3’5’H), 3-O-flavonoid glucosyltransferase (UFGT), and glutathione S-transferase (GST), softening related genes Polygalacturonase(PG), pectinate lyases(PL) and Pectin methylesterase( PME, as well as ethylene metabolism pathway-related genes 1-aminocyclopropane-1-carboxylic acid synthase 1(ACS1), 1-aminocyclopropane-1-carboxylic acid oxidase 2 (ACO2), ethylene receptor gene(ETR2), and ethylene-insensitive 3 (EIN3). Ethephon treatment also increased soluble solids and decreased titratable acid in grape fruit. Fruits pretreated with ethephon were inoculated with Botrytis cinerea, which led to resistance in grape fruit through activation of the antioxidant system. The expression levels of disease resistance-related genes including VvPAD4, VvPIP1, VvNAC26, VvDREB, VvAPX, Vvpgip, VvWRKY70, VvMYC2, VvNPR1 also increased in inoculated fruit with pathogen following ethephon pretreatment. Furthermore, we monitored ethylene response factor 1(ERF1) transcription factor, which could interact with protein EIN3 during ethylene signal transduction and mediate fruit resistance against B. cinerea infection. Meanwhile, overexpression of VvERF1 vectorin strawberry fruits reduced the susceptibility to B. cinerea infection. We suggest that ethylene can induce resistance in ripened fruits after B. cinerea infection and provide adequate postharvest care.

Ethylene Induced Flower Opening, Expression of Receptor Genes, and Antioxidant Defensive Responses in Cut Roses

The present research aimed to investigate the effect of ethylene on the physiological and molecular responses of the cut roses, Rosa hybrida L. Two cut rose cultivars (‘Amada +’ and ‘Brillante’) with different ethylene sensitivity were treated by 10 ppm exogenous ethylene for 24 h under identical vase life room conditions at partially open stage. The cultivars were then examined at both partially and fully open stage by gas chromatography, UV/Vis spectroscopy, and qRT-PCR. The cultivar with high sensitivity had lower total protein contents and showed higher ethylene production and antioxidant activity. Either exogenously applied ethylene or endogenously produced one resulted in increased antioxidant activity and decreased total protein contents. This observation is possibly because of enhanced free radical generation and protease activation with ethylene-induced flower opening and senescence. The qRT-PCR analysis showed a significant increase in the expression of ethylene signal transduction genes (RhETR1,3 and RhCTR1,2) of the treated cultivars with high sensitivity at commercial stage. However, there was a significant up-regulation of the RhETR1,3 genes in the cultivars with low sensitivity at fully-open stage. The ethylene induced responses were found highly dependent on the cultivar ability in both ethylene synthesis and perception.

LcEIL2/3 are involved in fruitlet abscission via activating genes related to ethylene biosynthesis and cell wall remodeling in litchi.

Fruit crops are subject to precocious fruit abscission, during which the phytohormone ethylene (ET) acts as a major positive regulator. However, the molecular basis of ET-induced fruit abscission remains poorly understood. Here, we show that two ETHYLENE INSENSITIVE 3-like (EIL) homologs in litchi, LcEIL2 and LcEIL3, play a role in ET-activated fruitlet abscission. LcEIL2/3 were significantly upregulated in the fruit abscission zone (AZ) during the ET-induced fruitlet abscission in litchi. The presence of LcEIL2/3 in wild-type Arabidopsis and ein3 eil1 mutants can accelerate the floral organ abscission. Moreover, the electrophoretic mobility shift assay and dual luciferase reporter analysis illustrated that LcEIL2/3 directly interacted with the gene promoters to activate the expression of cell wall remodeling genes LcCEL2/8 and LcPG1/2, and ET biosynthetic genes LcACS1/4/7 and LcACO2/3. Furthermore, we showed that LcPG1/2 were expressed in the floral abscission zone of Arabidopsis, and constitutive expression of LcPG2 in Arabidopsis promoted the floral organ abscission. In conclusion, we propose that LcEIL2/3 are involved in ET-induced fruitlet abscission via controlling expression of genes related to ET biosynthesis and cell wall remodeling in litchi.

Identification of EIL and ERF Genes Related to Fruit Ripening in Peach.

Peach (Prunus persica) is a climacteric fruit with a relatively short shelf life due to its fast ripening or softening process. Here, we report the association of gene families encoding ethylene insensitive-3 like (EIL) and ethylene response factor (ERF) with fruit ripening in peach. In total, 3 PpEILs and 12 PpERFs were highly expressed in fruit, with the majority showing a peak of expression at different stages. All three EILs could activate ethylene biosynthesis genes PpACS1 and PpACO1. One out of the 12 PpERFs, termed PpERF.E2, is a homolog of ripening-associated ERFs in tomato, with a consistently high expression throughout fruit development and an ability to activate PpACS1 and PpACO1. Additionally, four subgroup F PpERFs harboring the EAR repressive motif were able to repress the PpACO1 promoter but could also activate the PpACS1 promoter. Promoter deletion assay revealed that PpEILs and PpERFs could participate in transcriptional regulation of PpACS1 through either direct or indirect interaction with various cis-elements. Taken together, these results suggested that all three PpEILs and PpERF.E2 are candidates involved in ethylene biosynthesis, and EAR motif-containing PpERFs may function as activator or repressor of ethylene biosynthesis genes in peach. Our study provides an insight into the roles of EILs and ERFs in the fruit ripening process.

Uncertainty of EIN2Ser645/Ser924 Inactivation by CTR1-Mediated Phosphorylation Reveals the Complexity of Ethylene Signaling

ETHYLENE INSENSITIVE2 (EIN2) is a key component of ethylene signaling whose activity is inhibited upon phosphorylation of Ser645 and Ser924 by the Raf-like CONSTITUTIVE TRIPLE-RESPONSE 1 (CTR1) in the absence of ethylene. Ethylene prevents CTR1 activity and thus EIN2Ser645/Ser924 phosphorylation, and subcellular trafficking of a proteolytically cleaved EIN2 C terminus (EIN2-C) from the endoplasmic reticulum to the nucleus and processing bodies triggers ethylene signaling. Here, we report an unexpected complexity of EIN2-activated ethylene signaling. EIN2 activation in part requires ethylene in the absence of CTR1-mediated negative regulation. The ein2 mutant was complemented by the transgenes encoding EIN2, EIN2 variants with mutations that either prevent or mimic Ser645/Ser924 phosphorylation, or EIN2-C; and all the transgenic lines carrying these EIN2-derived transgenes responded to ethylene. Furthermore, we found that the fluorescence protein-tagged EIN2 and its variants were affected little by ethylene and exhibited similar subcellular distribution patterns: in the cytosolic particles and nuclear speckles. Of note, the subcellular localization patterns of EIN2 proteins fused with a fluorescence protein either at the N or C terminus were similar, whereas EIN2-C-YFP was primarily observed in the cytosol but not in the nucleus. Western blots and mass spectrum analyses suggested a high complexity of EIN2, which is likely proteolytically processed into multiple fragments. Our results suggested a nuclear localization of the full-length EIN2, weak association of the EIN2Ser645/Ser924 phosphorylation status and ethylene signaling, and the complexity of ethylene signaling caused by EIN2 and its proteolytic products in different subcellular compartments. We propose an alternative model to explain EIN2-activated ethylene signaling.

Preplant Application of 1-Methylcyclopropene Improves Postplanting Performance of Tomato Transplants by Suppressing Ethylene-induced Stress Responses

Transplant shock is caused by various types of abiotic stress, limiting stand establishment and productivity of many vegetable crops. Although postplanting stress can be minimized under well-managed field conditions, mechanical stress is unavoidable during the transport and transplanting of seedlings. Mechanical stress stimulates ethylene production, which in turn, induces overall growth retardation as a stress adaptation strategy. We hypothesized that, under optimum field conditions, transplant shock is caused primarily by ethylene-induced stress responses, and that inhibiting ethylene action can reduce transplant shock by maintaining uninterrupted growth. In this study, a new spray formulation of 1-methylcyclopropene (1-MCP) was used to inhibit ethylene perception in tomato (Solanum lycopersicum L.) seedlings. A bioassay experiment demonstrated reduced ethylene sensitivity in 1-MCP–treated (1 mg·L−1) seedlings using leaf epinasty and chlorosis as measured responses. Field experiments evaluated growth, physiological, and yield responses to preplant spray treatment of 1-MCP (12.5–50 mg·L−1) under optimum field conditions. Postplanting growth modulation by 1-MCP at the flowering stage was characterized by enhanced height growth and suppressed stem diameter growth, indicating the inhibition of ethylene-induced stress responses. At the fruit harvest stage, preplant 1-MCP treatment increased shoot biomass by 23% and flower production by 22%, while improving photosynthetic capacity on a whole-plant basis. As a result, 1-MCP–treated plants produced 13% to 24% higher total marketable fruit yields than untreated plants in two consecutive growing seasons. Correlation analyses revealed that flower number increased proportionally to shoot biomass, and marketable fruit number increased proportionally to flower number. These results support our hypothesis and propose that preplant 1-MCP treatment is a new stress-management approach to reducing transplant shock. Importantly, this new technique is easily implementable by commercial transplant nurseries with no negative side effect on transplant quality and fruit development.