ACC Synthase Research Articles

Mechanisms of the IAA and ACC-deaminase producing strain of Trichoderma longibrachiatum T6 in enhancing wheat seedling tolerance to NaCl stress

BackgroundTrichoderma species, a class of plant beneficial fungi, may provide opportunistic symbionts to induce plant tolerance to abiotic stresses. Here, we determined the possible mechanisms responsible for the indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate-deaminase (ACC-deaminase) producing strain of Trichoderma longibrachiatum T6 (TL-6) in promoting wheat (Triticum aestivum L.) growth and enhancing plant tolerance to NaCl stress.ResultsWheat treated with or without TL-6 was grown under different levels of salt stress in controlled environmental conditions. TL-6 showed a high level of tolerance to 10 mg ml− 1 of NaCl stress and the inhibitory effect was more pronounced at higher NaCl concentrations. Under NaCl stress, the activity of ACC-deaminase and IAA concentration in TL-6 were promoted, with the activity of ACC-deaminase increased by 26% at the salt concentration of 10 mg ml− 1 and 31% at 20 mg ml− 1, compared with non-saline stress; and the concentration of IAA was increased by 10 and 7%, respectively (P < 0.05). The increased ACC-deaminase and IAA concentration in the TL-6 strain may serve as an important signal to alleviate the negative effect of NaCl stress on wheat growth. As such, wheat seedlings with the ACC-deaminase and IAA producing strain of TL-6 treatment under NaCl stress increased the IAA concentration by an average of 11%, decreased the activity of ACC oxidase (ACO) by an average of 12% and ACC synthase (ACS) 13%, and decreased the level of ethylene synthesis and the content of ACC by 12 and 22%, respectively (P < 0.05). The TL-6 treatment decreased the transcriptional level of ethylene synthesis genes expression, and increased the IAA production genes expression significantly in wheat seedlings roots; down-regulated the expression of ACO genes by an average of 9% and ACS genes 12%, whereas up-regulated the expression of IAA genes by 10% (P < 0.05). TL-6 treatments under NaCl stress decreased the level of Na+ accumulation; and increased the uptake of K+ and the ratio of K+/Na+, and the transcriptional level of Na+/H+ antiporter gene expression in both shoots and roots.ConclusionsOur results indicate that the strain of TL-6 effectively promoted wheat growth and enhanced plant tolerance to NaCl stress through the increased ACC-deaminase activity and IAA production in TL-6 stain that modulate the IAA and ethylene synthesis, and regulate the transcriptional levels of IAA and ethylene synthesis genes expression in wheat seedling roots under salt stress, and minimize ionic toxicity by disturbing the intracellular ionic homeostasis in the plant cells. These biochemical, physiological and molecular responses helped promote the wheat seedling growth and enhanced plant tolerance to salt stress.

WRKY transcription factors in the response of table grapes (cv. Autumn Royal) to high CO2 levels and low temperature

WRKY transcription factors are regulated by biotic and abiotic stress in Vitis vinifera, although little is known about their role in grape berries. The latest V. vinifera reference genome (PN40024 12 × .v2, VCOST.v3 annotation) gave us a good opportunity to perform an analysis of VviWRKYs, identifying 61 genes. Our study examines whether the application of high CO2 levels for 3 d to maintain table grape quality activated the gene expression of 15 WRKYs in the skin and pulp of grapes (cv. Autumn Royal) stored at 0 °C. Results showed that the induction of VviWRKYs gene expression by CO2 was tissue dependent, being this effect mainly observed in the pulp where 9 out of the 15 genes analyzed were activated by the gaseous treatment. The expression analysis of genes associated with ethylene (ACC synthase1 (ACS1) and ACC oxidase1 (ACO1)) and ABA (9-cis-epoxycarotenoid dioxygenase1 (NCED1)) biosynthesis indicated that the expression of ACO1 in the skin of non-treated samples and in the pulp of CO2-treated ones correlated with the changes observed in VviWRKYs. In addition, we studied the role of WRKYs in the modulation of genes encoding pathogenesis-related proteins (PRs) in table grapes. Results showed there was a significant positive correlation between WRKYs modulated by CO2 in the skin and pulp with a β-1,3-glucanase (Vcgns1) and a thaumatin (VvTL1), respectively. Through electrophoretic mobility shift assay (EMSA) we observed that VviWRKYIIa_3 recombinant protein was able to in vitro bind to the W-box present in the promoter of the three PRs analyzed while VviWRKYIII_3 was only able to specifically bind to the Vcgns1 probe. Our results support the fact that high CO2 treatment is an active process that requires the activation of transcription factors, such as those of the WRKY family, which could participate in the molecular events involved in maintaining table grape quality during postharvest.

Induction of postharvest resistance in melon using pulsed light as abiotic stressor

The aim of this study was use the pulsed light (PL) as tool to booster the postharvest resistance in melons. Cantaloupe melons at mature stage were submitted to the treatments as follows: control, pulsed light (PL; 9 J cm−2), 1-methylcyclopropene (1-MCP; 600 nL L-1) and 1-MCP + PL (600 nL L-1 + 9 J cm−2). Postharvest resistance measurements according survival analysis developed at 4 °C, included: ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) oxidase activity, ACC synthase activity, firmness, pH, soluble solids, titratable acidity, SS/AT ratio, soluble sugars, vitamin C, total polyphenols, phenylalanine ammonia lyase (PAL) activity, colour epicarp, free polyamines (putrescine-Put, spermine-Spe and spermidine-Spd) and total polyamines (TPo). Combined effect of the PL+1-MCP promoted an additional of 12 days in the shelf life of melons. PL limited the ethylene biosynthesis leading to an immediate upregulation of polyamines (Put + Spe + Spd), hence, associated with high amounts of TPo (56%). PL treatment promoted an increase of PAL activity (67%) that synthesized high content of phenolic compounds (55%). The results suggest that PL with a fluence of 9 J cm−2 stimulate the postharvest defense mechanisms in melon, due to the ethylene production limitation, which was influenced by the increased polyamines, maintaining the quality attributes.

Transient induction of a subset of ethylene biosynthesis genes is potentially involved in regulation of grapevine bud dormancy release.

Transient increases in ethylene biosynthesis, achieved by tight regulation of transcription of specific ACC oxidase and ACC synthase genes, play a role in activation of grapevine bud dormancy release. The molecular mechanisms regulating dormancy release in grapevine buds are as yet unclear. It has been hypothesized that its core involves perturbation of respiration which induces an interplay between ethylene and ABA metabolism that removes repression and allows regrowth. Roles for hypoxia and ABA metabolism in this process have been previously supported. The potential involvement of ethylene biosynthesis in regulation of dormancy release, which has received little attention so far, is now explored. Our results indicate that (1) ethylene biosynthesis is induced by hydrogen cyanamide (HC) and azide (AZ), known artificial stimuli of dormancy release, (2) inhibitors of ethylene biosynthesis and signalling antagonize dormancy release by HC/AZ treatments, (3) ethylene application induces dormancy release, (4) there are two sets of bud-expressed ethylene biosynthesis genes which are differentially regulated, (5) only one set is transiently upregulated by HC/AZ and during the natural dormancy cycle, concomitant with changes in ethylene levels, and (6) levels of ACC oxidase transcripts and ethylene sharply decrease during natural dormancy release, whereas ACC accumulates. Given these results, we propose that transient increases in ethylene biosynthesis prior to dormancy release, achieved primarily by regulation of transcription of specific ACC oxidase genes, play a role in activation of dormancy release.

Effect of spermidine and D-arginine treatments on ethylene synthesis in Xinjiang ‘Saimaiti’ apricot

Xinjiang ‘Saimaiti’ apricots in the green ripe stage were used as the experimental materials. The apricots were treated with spermidine (Spd) and d-arginine (D-Arg). Fruit firmness, ethylene production, 1-aminocyclopropane-1-carboxylic-acid (ACC) synthase activity, ACC oxidase activity and gene expression were studied. The results show that Spd treatment could delay the decline of fruit firmness and reduce ACC synthase and ACC oxidase activity through the inhibition of the relative expression of PaACS2 and PaACO, thus further reducing ethylene production and delaying senescence. Inhibition of polyamine synthesis due to d-Arg treatment can increase the activity of ethylene related enzymes and promote ethylene production. The results suggested that Spd treatment inhibits ethylene production. PaACS2 was the key gene involved in regulating the maturation and senescence of ‘Saimaiti’ apricots.

Arabidopsis ACC Oxidase 1 Coordinated by Multiple Signals Mediates Ethylene Biosynthesis and Is Involved in Root Development.

Ethylene regulates numerous aspects of plant growth and development. Multiple external and internal factors coordinate ethylene production in plant tissues. Transcriptional and post-translational regulations of ACC synthases (ACSs), which are key enzymes mediating a rate-limiting step in ethylene biosynthesis have been well characterized. However, the regulation and physiological roles of ACC oxidases (ACOs) that catalyze the final step of ethylene biosynthesis are largely unknown in Arabidopsis. Here, we show that Arabidopsis ACO1 exhibits a tissue-specific expression pattern that is regulated by multiple signals, and plays roles in the lateral root development in Arabidopsis. Histochemical analysis of the ACO1 promoter indicated that ACO1 expression was largely modulated by light and plant hormones in a tissue-specific manner. We demonstrated that point mutations in two E-box motifs on the ACO1 promoter reduce the light-regulated expression patterns of ACO1. The aco1-1 mutant showed reduced ethylene production in root tips compared to wild-type. In addition, aco1-1 displayed altered lateral root formation. Our results suggest that Arabidopsis ACO1 integrates various signals into the ethylene biosynthesis that is required for ACO1’s intrinsic roles in root physiology.

Diversification of NOR-like genes resulted in functional similarity in tomato

Fruit shelf life is an important tomato breeding trait. Ethylene production greatly affects shelf life and is genetically regulated. Tomato ripening is associated with increased ethylene production, and tomato is used as a model for studying fruit ripening, particularly the ethylene biosynthesis and signaling pathways. The key ripening regulator NOR encodes a NAC domain transcription factor which is part of a large plant-specific gene family. Both CRES-T and RNAi gene suppression transgenic lines revealed delayed ripening signs. Further screening of the Micro-Tom ethyl methanesulfonate (EMS)-mutagenized population enabled the selection of alleles responsible for phenotype alterations. Analyses of the transcription levels of ethylene biosynthesis genes ACC synthase (ACS) and ACC-oxidase (ACO) revealed that reduced ethylene production was largely due to transcriptional suppression of ACO1 and ACO3. ACO failed to oxidize the ethylene precursor, thus producing a non-climacteric phenotype in nor. Evidence indicated possible feedback regulation of NOR and cross-regulation of NOR-like genes, and functional conservation suggests that NAC coding genes may undergo functional differentiation. NOR plays a major role in ripening control, whereas NOR-like genes have a minor role; however, a better understanding of NOR-like genes could provide insights into the complex transcriptional regulation of fruit ripening.

Analysis of ethylene-induced gene regulation during carposporogenesis in the red seaweed Grateloupia imbricata (Rhodophyta).

Ethylene favors carposporogenesis in the red seaweed Grateloupia imbricata. Analyses of cystocarp development invitro in thalli treated with ethylene suggest an interconnection between polyamine and ethylene biosynthesis pathways. Yet, little is known about molecular mechanisms underlying carposporogenesis. Here, we used droplet digital PCR to analyze genes encoding enzymes related to polyamine (Spermidine [Spd] synthase) and ethylene (ACC synthase) synthesis; a pivotal compound of both pathways (S-adenosyl methionine synthase, SAMS); the gene that encodes amine oxidase, which is involved in polyamine degradation, and a candidate gene involved in seaweed reproduction (ornithine decarboxylase, ODC). In addition, we analyzed genes encoding proteins related to stress and reactive oxygen species, ascorbate peroxidase (APX), cytochrome P450 and WD 40. We characterized gene expression in fertilized and fertile thalli from G.imbricata that were exposed to ethylene for 15min at two time points after treatment (1 and 7d). The differential gene expression of SAMS, Spd synthase, ACC synthase, and cytochrome P450 was related to disclosure and development of cystocarps in fertilized thalli that transitioned from having no visible cystocarps at 1d to developing cystocarps at 7d. Likewise, cytochrome P450 was associated with cystocarp disclosure and maturation. In addition, amine oxidase and APX were involved in fine-tuning polyamine and reactive oxygen species during carposporogenesis, respectively, whereas WD 40 did so in relation to ethylene signaling. Expression of the candidate gene ODC was increased when cystocarps were not visible (fertilized thalli, 1d), as previously described. This analysis suggests developmental stage-specific roles for these genes during carposporogenesis.

Ethylene biosynthesis controlled by NON-RIPENING: A regulatory conflict between wounding and ripening

The phytohormone ethylene is involved in multiple aspects of morphological and physiological processes in plants. Tomato rapidly and transiently increases ethylene production during fruit ripening and in plant defense responses. The transcription factor non-ripening (NOR) has significant effects on fruit ripening via regulation of ethylene biosynthesis-related genes. The nor loss-of-function allele produces a basal level of ethylene during ripening, in contrast to the induced ethylene evolution observed upon Agrobacterium tumefaciens infection. The use of ACC deaminase represses ethylene production and significantly improves the efficiency of Agrobacterium-mediated T-DNA transfer in nor plants. Analyses of the transcription levels of the ethylene biosynthesis genes ACC synthase (ACS) and ACC oxidase (ACO) in nor plants revealed that the induced ethylene production was largely due to transcriptional accumulation of ACS2 and ACO1. Accumulation of ACS2 and ACO1 mRNA opposes NOR-mediated regulation in tomato fruit during ripening, and the feedback regulation of NOR is rendered ineffective by defense responses, thereby precluding the control of its own expression. The ethylene synthesis mechanisms respond properly to NOR-mediated transcriptional regulation that is differed through the wound-induced and ripening-induced signaling pathway.

Expression of grape ACS1 in tomato decreases ethylene and alters the balance between auxin and ethylene during shoot and root formation

Ethylene plays an important role in the grape rachis, where its production can be 10 times higher than in the berry. VvACS1 is the only rachis-specific ACC synthase (ACS) gene, and its expression is coincident with ethylene production in the rachis of Vitis vinifera ‘Thompson seedless’. VvACS1 was cloned and ectopically expressed in tomato (Solanum lycopersicum ‘Moneymaker’). Lateral buds were increased in two- or four-week-old 35s∷VvACS1 transgenic tomato plants after transplanting. Compared with wild-type (WT) plants, the transgenic tomato plants showed higher expression of the VvACS1 gene in the flowers, leaves, rachis, and fruits. There was no obvious difference of ACS activity in the fruit of tomato, and only increased ACS activity in the rachis of tomato. Ethylene production was decreased in flowers, leaves, and fruits (seven weeks after full bloom), while the relative expression of endogenous tomato ACS1 and ACS6 genes was not down-regulated by the ectopic expression of VvACS1. These results imply that post-transcriptional or post-translational regulation of ACS may occur, resulting in lower ethylene production in the transgenic tomato plants. Moreover, expression of VvACS1 in tomato resulted in decreased auxin and increased zeatin contents in the lateral buds, as well as reduced or delayed formation of adventitious roots in lateral bud cuttings. RNA-Seq and qRT-PCR analyses of rooted lateral bud cuttings indicated that the relative expression levels of the genes for zeatin O-glucosyltransferase-like, auxin repressed/dormancy-associated protein, and ERF transcription factors were higher in transgenic tomatoes than in WT, suggesting that ethylene may regulate auxin transport and distribution in shoots and that adventitious root formation employs coordination between auxin and ethylene.

Novel functions of the Arabidopsis transcription factor TCP5 in petal development and ethylene biosynthesis.

SummaryThe flowers of most dicotyledons have petals that, together with the sepals, initially protect the reproductive organs. Later during development petals are required to open the flower and to attract pollinators. This diverse set of functions demands tight temporal and spatial regulation of petal development. We studied the functioning of the Arabidopsis thaliana TCP5‐like transcription factors (TFs) in petals. Overexpression of TCP5 in petal epidermal cells results in smaller petals, whereas tcp5 tcp13 tcp17 triple knockout lines have wider petals with an increased surface area. Comprehensive expression studies revealed effects of TCP5‐like TFs on the expression of genes related to the cell cycle, growth regulation and organ growth. Additionally, the ethylene biosynthesis genes 1‐amino‐cyclopropane‐1‐carboxylate (ACC) synthase 2 (ACS2) and ACC oxidase 2 (ACO2) and several ETHYLENE RESPONSE FACTORS (ERFs) are found to be differentially expressed in TCP5 mutant and overexpression lines. Chromatin immunoprecipitation–quantitative PCR showed direct binding of TCP5 to the ACS2 locus in vivo. Ethylene is known to influence cell elongation, and the petal phenotype of the tcp5 tcp13 tcp17 mutant could be complemented by treatment of the plants with an ethylene pathway inhibitor. Taken together, this reveals a novel role for TCP5‐like TFs in the regulation of ethylene‐mediated petal development and growth.

Auxin Acts Downstream of Ethylene and Nitric Oxide to Regulate Magnesium Deficiency-Induced Root Hair Development in Arabidopsis thaliana.

This study examines the association of auxin with ethylene and nitric oxide (NO) in regulating the magnesium (Mg) deficiency-induced root hair development in Arabidopsis thaliana. With Mg deficiency, both ethylene and NO promoted the elevation of root auxin levels in roots by inducing the expression of AUXIN-RESISTANT1 (AUX1), PIN-FORMED 1 (PIN1) and PIN2 transporters. In turn, auxin stimulated ethylene and NO production by activating the activities of 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO), ACC synthase (ACS), nitrate reductase (NR) and NO synthase-like (NOS-L). These processes constituted an NO/ethylene-auxin feedback loop. Interestingly, however, the roles of ethylene and NO in regulating Mg deficiency-induced root hair development required the action of auxin, but not vice versa. In summary, these results suggest that Mg deficiency induces a positive interaction between the accumulation of auxin and ethylene/NO in roots, with auxin acting downstream of ethylene and NO signals to regulate Mg deficiency-induced root hair morphogenesis.

Ethylene-Related Gene Expression Networks in Wood Formation.

Thickening of tree stems is the result of secondary growth, accomplished by the meristematic activity of the vascular cambium. Secondary growth of the stem entails developmental cascades resulting in the formation of secondary phloem outwards and secondary xylem (i.e., wood) inwards of the stem. Signaling and transcriptional reprogramming by the phytohormone ethylene modifies cambial growth and cell differentiation, but the molecular link between ethylene and secondary growth remains unknown. We addressed this shortcoming by analyzing expression profiles and co-expression networks of ethylene pathway genes using the AspWood transcriptome database which covers all stages of secondary growth in aspen (Populus tremula) stems. ACC synthase expression suggests that the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is synthesized during xylem expansion and xylem cell maturation. Ethylene-mediated transcriptional reprogramming occurs during all stages of secondary growth, as deduced from AspWood expression profiles of ethylene-responsive genes. A network centrality analysis of the AspWood dataset identified EIN3D and 11 ERFs as hubs. No overlap was found between the co-expressed genes of the EIN3 and ERF hubs, suggesting target diversification and hence independent roles for these transcription factor families during normal wood formation. The EIN3D hub was part of a large co-expression gene module, which contained 16 transcription factors, among them several new candidates that have not been earlier connected to wood formation and a VND-INTERACTING 2 (VNI2) homolog. We experimentally demonstrated Populus EIN3D function in ethylene signaling in Arabidopsis thaliana. The ERF hubs ERF118 and ERF119 were connected on the basis of their expression pattern and gene co-expression module composition to xylem cell expansion and secondary cell wall formation, respectively. We hereby establish data resources for ethylene-responsive genes and potential targets for EIN3D and ERF transcription factors in Populus stem tissues, which can help to understand the range of ethylene targeted biological processes during secondary growth.

The FBH family of bHLH transcription factors controls ACC synthase expression in sugarcane.

Ethylene is a phytohormone involved in the regulation of several aspects of plant development and in responses to biotic and abiotic stress. The effects of exogenous application of ethylene to sugarcane plants are well characterized as growth inhibition of immature internodes and stimulation of sucrose accumulation. However, the molecular network underlying the control of ethylene biosynthesis in sugarcane remains largely unknown. The chemical reaction catalyzed by 1-aminocyclopropane-1-carboxylic acid synthase (ACS) is an important rate-limiting step that regulates ethylene production in plants. In this work, using a yeast one-hybrid approach, we identified three basic helix-loop-helix (bHLH) transcription factors, homologs of Arabidopsis FBH (FLOWERING BHLH), that bind to the promoter of ScACS2 (Sugarcane ACS2), a sugarcane type 3 ACS isozyme gene. Protein-protein interaction assays showed that sugarcane FBH1 (ScFBH1), ScFBH2, and ScFBH3 form homo- and heterodimers in the nucleus. Gene expression analysis revealed that ScFBHs and ScACS2 transcripts are more abundant in maturing internodes during afternoon and night. In addition, Arabidopsis functional analysis demonstrated that FBH controls ethylene production by regulating transcript levels of ACS7, a homolog of ScACS2. These results indicate that ScFBHs transcriptionally regulate ethylene biosynthesis in maturing internodes of sugarcane.

Role of ethylene and related gene expression in the interaction between strawberry plants and the plant growth-promoting bacterium Azospirillum brasilense.

Induced systemic resistance (ISR) is one of the indirect mechanisms of growth promotion exerted by plant growth-promoting bacteria, and can be mediated by ethylene (ET). We assessed ET production and the expression of related genes in the Azospirillum-strawberry plant interaction. Ethylene production was evaluated by gas chromatography in plants inoculated or not with A.brasilense REC3. Also, plants were treated with AgNO3 , an inhibitor of ET biosynthesis; with 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ET biosynthesis; and with indole acetic acid (IAA). Plant dry biomass and the growth index were determined to assess the growth-promoting effect of A.brasilense REC3 in strawberry plants. Quantitative real time PCR (qRT-PCR) was performed to analyse relative expression of the genes Faetr1, Faers1 and Faein4, which encode ET receptors; Factr1 and Faein2, involved in the ET signalling pathway; Faacs1 encoding ACC synthase; Faaco1 encoding ACC oxidase; and Faaux1 and Faami1 for IAA synthesis enzymes. Results showed that ET acts as a rapid and transient signal in the first 12h post-treatment. A.brasilense REC3-inoculated plants had a significantly higher growth index compared to control plants. Modulation of the genes Faetr1, Faers1, Faein4, Factr1, Faein2 and Faaco1 indicated activation of ET synthesis and signalling pathways. The up-regulation of Faaux1 and Faami1 involved in IAA synthesis suggested that inoculation with A.brasilense REC3 induces production of this auxin, modulating ET signalling. Ethylene production and up-regulation of genes associated with ET signalling in strawberry plants inoculated with A.brasilense REC3 support the priming activation characteristic of ISR. This type of resistance and the activation of systemic acquired resistance previously observed in this interaction indicate that both are present in strawberry plants, could act synergistically and increase protection against pathogens.

Regulation of the protein and gene expressions of ethylene biosynthesis enzymes under different temperature during peach fruit ripening

Ethylene has profound effect on fruit development and ripening, and the role of ethylene biosynthesis enzymes involving 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS), ACC oxidase (ACO), and S-Adenosyl-l-methionine synthetase (SAMS) in peach fruit (cv. Xiahui-8) was characterized under 25 and 4 °C, respectively. All these enzymes in ethylene synthesis pathway were identified using 2-DE and real-time PCR. Both protein and gene expressions of ACO and SAMS were much higher at 25 °C than at 4 °C. Among five members of ACS family, PpaACS4 may belong to system II ethylene biosynthesis, while PpaACS3 involved in system I during development stage, and low temperature can induce PpaACS1 expression. The ethylene release and low expressions of proteins and genes of most enzymes indicated that low temperature can effectively postpone ripening stage by reducing ethylene evolution. High gene expression of PpaSAMS did not cause excessive expression of SAMS protein under low temperature, and over-expression of PpaACS1 at low temperature still did not induce increase of ethylene production. The mechanism underlying the phenomenon about how temperature affects ethylene release was also discussed.

Effects of the inoculations using bacteria producing ACC deaminase on ethylene metabolism and growth of wheat grown under different soil water contents

Crop growth and productivity are often impacted by the increased ethylene content induced by adverse environmental conditions such drought. Inoculations with bacteria producing ACC deaminase is considered as a potential biological approach to improve the growth and tolerance of stressed plants by lowering endogenous ethylene level. In this study, germinated wheat seeds were inoculated using three species of the rhizobacteria, which were isolated from the rhizosphere of wheat growing in dryland, and sown in pots. After three weeks, wheat seedlings were exposed to non-limiting water condition, medium drought and severe drought, respectively, for six weeks. The results showed that, irrespective of rhizobacterial inoculations, decreased soil water contents stimulated wheat ethylene metabolism, which was reflected by the significantly increased activity of ACC synthetase and ACC oxidase, besides an increased content of ACC both in the roots and leaves, and an enhanced capacity of leaves to release ethylene, concomitant with a significant decline in shoot and roots biomass. The inoculations of all three rhizobacterial species under each water condition reduced ACC content in wheat leaves, but effects of the inoculations on ACC synthase and ACC oxidase activity in the leaves and roots, ACC content in the roots, the capacity of leaves to release ethylene, and wheat growth varied with water conditions and bacterial species. Hence, both soil water conditions and rhizobacterial inoculations acted on all the processes of ethylene metabolism, with the former being dominant. The inoculations under non-limiting water condition and medium drought promoted shoot and root growth of wheat plants.

RNA expression, protein activity, and interactions in the ACC synthase gene family in cucumber (Cucumis sativus L.)

Ethylene is an important regulator of developmental and stress responses in plants, and 1-aminocyclopropane-1-carboxylic acid synthase (ACS) proteins catalyze one of the rate-limiting steps in endogenous ethylene biosynthesis. Accordingly, the function of ACS family genes has been extensively studied in plants including Arabidopsis and tomato; however, little is known about the systemic function of ACS genes in cucumber (Cucumis sativus L.). Here, we investigated the expression patterns of eight cucumber ACS family genes (CsACSs) in a variety of tissues and sex types, as well as in response to exogenous ethylene application, and their ACS activities. Tissue-specific expression profiling in monoecious and gynoecious cucumber plants revealed that some CsACSs were differentially expressed. In particular, the five genes CsACS1, CsACS1-2, CsACS2, CsACS6, and CsACS11 were highly expressed in the shoot apex regions of gynoecious and hermaphroditic cucumber plants. The expression of most CsACSs was also induced by exogenous ethylene application. Furthermore, three CsACS isoforms (CsACS9, CsACS10, and CsACS12) showed no ACS enzymatic activity, which was associated with the amino acid variations in the conserved active residues of CsACS proteins. However, an in vitro pull-down assay revealed that two enzymatically inactive isoforms (CsACS9 and CsACS10) did not significantly interact with four active isoforms (CsACS1, CsACS1-2, CsACS2, and CsACS6). Taken together, our findings will be valuable for elucidating the relationship between RNA expression, ACS activity, protein–protein interactions between CsACSs and cucumber sex types.

Arabidopsis thalianaACS8 plays a crucial role in the early biosynthesis of ethylene elicited by Cu2+ ions.

Cu2+ ions are required by all living organisms and play important roles in many bactericides and fungicides. We previously reported that Cu2+ can elicit defense responses, which are dependent on the ethylene signaling pathway in Arabidopsis However, the mechanism by which Cu2+ elicits the biosynthesis of ethylene remains unclear. Here, we show that CuSO4 treatment rapidly increases the production of ethylene. In addition, it upregulates the expression of several defense-related genes and ethylene biosynthesis genes, including genes encoding S-adenosylmethionine synthase, 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase. Among these genes, Arabidopsis thaliana (At)ACS8 was identified as essential for the defense response and early ethylene biosynthesis induced by Cu2+ Furthermore, Cu2+-induced AtACS8 expression depended on the copper-response cis-element (CuRE) in the promoter of AtACS8 Our study indicates that Cu2+ specifically activates the expression of AtACS8 to promote the early biosynthesis of ethylene that elicits plant immunity in Arabidopsis plants.

Increased chalcone synthase (CHS) expression is associated with dicamba resistance in Kochia scoparia.

Resistance to the synthetic auxin herbicide dicamba is increasingly problematic in Kochia scoparia. The resistance mechanism in an inbred dicamba-resistant K. scoparia line (9425R) was investigated using physiological and transcriptomics (RNA-Seq) approaches. No differences were found in dicamba absorption or metabolism between 9425R and a dicamba-susceptible line, but 9425R was found to have significantly reduced dicamba translocation. Known auxin-responsive genes ACC synthase (ACS) and indole-3-acetic acid amino synthetase (GH3) were transcriptionally induced following dicamba treatment in dicamba-susceptible K. scoparia but not in 9425R. Chalcone synthase (CHS), the gene regulating synthesis of the flavonols quertecin and kaemperfol, was found to have twofold higher transcription in 9425R both without and 12 h after dicamba treatment. Increased CHS transcription co-segregated with dicamba resistance in a forward genetics screen using an F2 population. Prior work has shown that the flavonols quertecin and kaemperfol compete with auxin for intercellular movement and vascular loading via ATP-binding cassette subfamily B (ABCB) membrane transporters. The results of this study support a model in which constitutively increased CHS expression in the meristem produces more flavonols that would compete with dicamba for intercellular transport by ABCB transporters, resulting in reduced dicamba translocation. © 2017 Society of Chemical Industry.