Ethylene Biosynthetic Pathway Research Articles

Five improved sesame reference genomes and genome resequencing unveil the contribution of structural variants to genetic diversity and yield-related traits variation.

Five improved sesame reference genomes and genome resequencing unveil the contribution of structural variants to genetic diversity and yield-related traits variation.

A Revised View of the LSU Gene Family: New Functions in Plant Stress Responses and Phytohormone Signaling.

LSUs (RESPONSE TO LOW SULFUR) are plant-specific proteins of unknown function that were initially identified during transcriptomic studies of the sulfur deficiency response in Arabidopsis. Recent functional studies have shown that LSUs are important hubs of protein interaction networks with potential roles in plant stress responses. In particular, LSU proteins have been reported to interact with members of the brassinosteroid, jasmonate signaling, and ethylene biosynthetic pathways, suggesting that LSUs may be involved in response to plant stress through modulation of phytohormones. Furthermore, in silico analysis of the promoter regions of LSU genes in Arabidopsis has revealed the presence of cis-regulatory elements that are potentially responsive to phytohormones such as ABA, auxin, and jasmonic acid, suggesting crosstalk between LSU proteins and phytohormones. In this review, we summarize current knowledge about the LSU gene family in plants and its potential role in phytohormone responses.

Myo-inositol phosphate synthase improves heat stress tolerance by ethylene-mediated modulation of chlorophyll content and photosynthetic efficiency.

L-myo-inositol phosphate synthase (MIPS; EC 5.5.1.4) encodes the enzyme synthesizing Myo-inositol for plant growth and development. Myo-inositol and its phosphate derivatives are involved in various physiological functions ranging from cell wall synthesis, chromatin remodeling, signal transduction, and providing stress responses. In the present study, we report that MIPS regulates chlorophyll content and photosynthesis efficiency via the ethylene signaling pathway. We have used Triticum aestivum MIPS-A (TAMIPS-A) for the present study and characterized it by mutant complementation and overexpression studies in Arabidopsis. TaMIPS-A overexpressing Arabidopsis transgenics were analyzed physiologically under thermal stress conditions. Analysis of overexpression TaMIPS-A transgenics under control and thermal stress conditions revealed them to have enhanced photosynthetic potential under heat stress. When TaMIPS-A overexpression (OE) Arabidopsis transgenics are supplemented with either ACC, the ethylene precursor, or AgNO3, the ethylene signaling inhibitor indicated that MIPS regulates the photosynthetic efficiency and chlorophyll content via the ethylene signaling pathway under control and thermal stress. Expression analysis of essential genes involved in the ethylene biosynthetic and signaling pathway corroborated.

Increased ACS Enzyme Dosage Causes Initiation of Climacteric Ethylene Production in Tomato.

Fruits of wild tomato species show different ethylene-dependent ripening characteristics, such as variations in fruit color and whether they exhibit a climacteric or nonclimacteric ripening transition. 1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) are key enzymes in the ethylene biosynthetic pathway encoded by multigene families. Gene duplication is a primary driver of plant diversification and angiosperm evolution. Here, interspecific variations in the molecular regulation of ethylene biosynthesis and perception during fruit ripening in domesticated and wild tomatoes were investigated. Results showed that the activated ACS genes were increased in number in red-ripe tomato fruits than in green-ripe tomato fruits; therefore, elevated dosage of ACS enzyme promoted ripening ethylene production. Results showed that the expression of three ACS isogenes ACS1A, ACS2, and ACS4, which are involved in autocatalytic ethylene production, was higher in red-ripe tomato fruits than in green-ripe tomato fruits. Elevated ACS enzyme dosage promoted ethylene production, which corresponded to the climacteric response of red-ripe tomato fruits. The data suggest that autoinhibitory ethylene production is common to all tomato species, while autocatalytic ethylene production is specific to red-ripe species. The essential regulators Non-ripening (NOR) and Ripening-Inhibitor (RIN) have experienced gene activation and overlapped with increasing ACS enzyme dosage. These complex levels of transcript regulation link higher ethylene production with spatiotemporal modulation of gene expression in red-ripe tomato species. Taken together, this study shows that bursts in ethylene production that accompany fruit color changes in red-ripe tomatoes are likely to be an evolutionary adaptation for seed dispersal.

TaMYC8 regulates TaERF6 and inhibits ethylene synthesis to confer Cd tolerance in wheat

Cadmium (Cd) is a toxic, nonessential heavy metal; its accumulation in plants alters metabolism and limits productivity. Although various studies have addressed the Cd stress response in various species, the detailed molecular mechanisms remain unknown. Therefore, the present work investigated the influence of the TaMYC8 transcription factor (TF) on the Cd-induced stress response in wheat. The present study found that TaMYC8 is a nuclear protein highly induced in the roots under Cd stress. Overexpression of TaMYC8 in the wheat cultivar ‘Bobwhite’ increased sensitivity to Cd stress, probably due to the increased levels of superoxide (O 2 .- ), malonaldehyde (MDA), jasmonic acid (JA), and Cd, and reduced the proline content and antioxidant enzyme activity. In contrast, silencing TaMYC8 via RNA interference (RNAi) significantly lowered Cd accumulation and improved Cd tolerance. Using the yeast one-hybrid assay (Y1H), chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP–qPCR), electrophoretic mobility shift assay (EMSA), and dual luciferase reporter assay, it was found that TaMYC8 could physically bind to the TaERF6 promoter and activate TaERF6 transcription. More importantly, knockdown of TaMYC8 by RNAi inhibited the activities of 1-aminocyclopropane-1-carboxylic (ACC) acid synthase (ACS) and ACC oxidase (ACO) of the ethylene biosynthetic pathway. In conclusion, TaMYC8 promotes TaERF6 transcription and affects the ethylene biosynthetic pathway. These findings provide a theoretical basis for breeding low-Cd-accumulating wheat cultivars. • TaMYC8 decreased Cd tolerance of transgenic wheat . • TaMYC8 binds to the promoter of TaERF6 as well as regulating the transcription of TaERF6 . • TaMYC8 affects Cd tolerance of wheat by regulating ethylene synthesis .

Ethylene and polyamines form a negative feedback loop to regulate peach fruit ripening via the transcription factor PpeERF113 by regulating the expression of PpePAO1

Ethylene and polyamines (PAs) have antagonistic roles during fruit ripening. PAs affect both ethylene biosynthetic and signal transduction pathways, but the regulatory effects of ethylene on PA metabolism during fruit ripening have remained largely unknown. Here, we found that ethylene enhanced PA catabolism by regulating expression of a peach PA oxidase gene, PpePAO1. Knocking out PpePAO1 delayed peach fruit ripening, whereas PpePAO1 overexpression promoted tomato fruit ripening. Both in vitro and in vivo assays demonstrated that an ethylene response factor (ERF), PpeERF113, activated PpePAO1 by direct binding to the promoter. PA levels were significantly increased and ripening was delayed in PpeERF113 knockdown peach fruit. Correspondingly, PA levels were significantly decreased when PpeERF113 was overexpressed in peach. PpeERF113 was also found to be upregulated in PpePAO1 knockdowns, indicating that PA catabolism has a regulatory function in ethylene signal transduction. Together, our results suggest that ethylene accelerates peach fruit ripening in part by promoting PA catabolism through PpeERF113-mediated regulation of PpePAO1 expression. To our knowledge, this is the first report related to the regulatory mechanism of ethylene in PA catabolism during fruit ripening. This study contributes new understanding of the crosstalk between ethylene and PAs during fruit ripening.

A long noncoding RNA functions in high-light-induced anthocyanin accumulation in apple by activating ethylene synthesis.

Anthocyanin production in apple (Malus domestica) fruit and their consequent coloration can be induced by high-light treatment. The hormone ethylene is also essential for this coloration, but the regulatory relationships that link ethylene and light with anthocyanin-associated coloration are not well defined. In this study, we observed that high-light treatment of apple fruit increased anthocyanin accumulation more than moderate-light treatment did and was the main contributor of induced ethylene production and activation of anthocyanin biosynthesis. A transcriptome study of light-treated apple fruit suggested that a long noncoding RNA (lncRNA), MdLNC610, the corresponding gene of which is physically located downstream from the 1-aminocyclopropane-1-carboxylate oxygenase (ACO) ethylene biosynthesis gene MdACO1, likely affects anthocyanin biosynthesis under high-light treatment. Expression and promoter β-glucuronidase reporter analyses further showed that MdLNC610 upregulates expression of MdACO1 and so likely participates in high-light-induced ethylene biosynthesis. Overexpression of MdACO1 and MdLNC610 in apple fruit and calli indicated that a major increase in MdLNC610 expression activates MdACO1 expression, thereby causing an increase in ethylene production and anthocyanin levels. These results suggest that MdLNC610 participates in the regulation of high-light-induced anthocyanin production by functioning as a positive regulator to promote MdACO1 expression and ethylene biosynthesis. Our study provides insights into the relationship between mRNA and lncRNA networks in the ethylene biosynthetic pathway and anthocyanin accumulation in apple fruit.

Characterizing the effects of different chemicals on stem bending of cut snapdragon flower

BackgroundThis study investigated the effects of ethylene release compounds (ethephon), ethylene-action inhibitors (silver thiosulfate: STS), and nitric oxide donor (sodium nitroprusside: SNP) on stem bending of snapdragon flowers. Moreover, the effects of plant growth supplements [6-benzyladenine (BA), gibberellic acid 3 (GA3), and calcium chloride (CaCl2)] on the stem bending were also extensively investigated.ResultsEthephon completely prevented stem bending until 9 days after treatment (9 DAT). STS exhibited the highest bending rate, while SNP did not significantly affect the bending compared to the controls. The bending results were associated with the results of stem curvature, relative shoot elongation, ethylene production, and lignin content, that are involved in the stem bending mechanism. This was proven by the expression analysis of genes involved in ethylene and lignin biosynthetic pathways. The addition of plant growth supplements slightly or significantly delayed stem bending in the treatments (control, SNP, and STS) and significantly reduced petal senescence in ethephon at 9 DAT.ConclusionThese results show the preventive role of ethephon in the stem bending of cut snapdragon. Moreover, the combination of ethephon with supplements also provided information that could guide the development of strategies to delay stem bending in other cut flowers that undergo serious bending during a short vase life.

Overexpression of watermelon ClWRKY20 in transgenic Arabidopsis improves salt and low-temperature tolerance

The WRKY transcription factor plays an important regulatory role in plant responses to biotic and abiotic stressors. In this study, ClWRKY20, whose expression was strongly induced by chilling in watermelon, was isolated and characterized. ClWRKY20 belongs to group III of the WRKY family. The subcellular localization analysis found that ClWRKY20 was localized only in the nucleus. Expression characteristic analysis found that it was upregulated in response to drought, salt, and exogenous phytohormones, including salicylic acid (SA), ethylene (ET), and abscisic acid (ABA). The overexpression of ClWRKY20 enhanced the salt and low-temperature tolerance of transgenic Arabidopsis determined through apparent symptoms and physiological analyses of the root growth, the lethal rate, the relative electrical leakage, MDA and proline contents, the seed germination rate, and the Fv/Fm value. Furthermore, the ClWRKY20 overexpression lines showed increased sensitivity to ABA during seed germination, while did not at the seedling stage. The RNA sequencing and quantitative real-time PCR analyses revealed that several stress-related genes induced by chilling stress in wild-type plants were also upregulated by the overexpression of ClWRKY20 in transgenic plants, relative to their expressions in the WT Arabidopsis. Additionally, transcript levels of several genes involved in the ABA signaling pathway, in the ethylene biosynthetic and ethylene signaling pathway, in the jasmonic acid biosynthesis and jasmonate signaling, or related to auxin transport and auxin-responsive, were significantly increased in the transgenic Arabidopsis compared with that in the WT plants. Taken together, ClWRKY20 positively modulated plant tolerance to salt and low temperature stresses, and the enhanced chilling tolerance in transgenic Arabidopsis was accompanied by the increased expressions of stress-related genes. Moreover, ClWRKY20 not only modulated chilling responses through ABA signaling, but also might function as an integrator among several signaling pathways.

The B’ζ subunit of protein phosphatase 2A negatively regulates ethylene signaling in Arabidopsis

Ethylene is a major plant hormone that regulates plant growth, development, and defense responses to biotic and abiotic stresses. The major pieces of the ethylene signaling pathway have been put together, although several details still need to be elucidated. For instance, the phosphorylation and dephosphorylation processes controlling the ethylene responses are poorly understood and need to be further explored. The type 2A protein phosphatase (PP2A) was suggested to play an important role in the regulation of ethylene biosynthesis, where the A1 subunit of PP2A was shown to be involved in the regulation of the rate-limiting enzyme of the ethylene biosynthetic pathway. However, whether other subunits of PP2A play roles in the ethylene signal transduction pathway is yet to be answered. In this study, we demonstrate that a B subunit, PP2A-B’ζ, positively regulates plant germination and seedling development, as a pp2a-b’ζ mutant is very sensitive to ethylene treatment. Furthermore, PP2A-B’ζ interacts with and stabilizes the kinase CTR1 (Constitutive Triple Response 1), a key enzyme in the ethylene signal transduction pathway, and like CTR1, PP2A-B’ζ negatively regulates ethylene signaling in plants.

Phytohormone Production Profiles in Trichoderma Species and Their Relationship to Wheat Plant Responses to Water Stress.

The production of eight phytohormones by Trichoderma species is described, as well as the 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD) activity, which diverts the ethylene biosynthetic pathway in plants. The use of the Trichoderma strains T. virens T49, T. longibrachiatum T68, T. spirale T75 and T. harzianum T115 served to demonstrate the diverse production of the phytohormones gibberellins (GA) GA1 and GA4, abscisic acid (ABA), salicylic acid (SA), auxin (indole-3-acetic acid: IAA) and the cytokinins (CK) dihydrozeatin (DHZ), isopenteniladenine (iP) and trans-zeatin (tZ) in this genus. Such production is dependent on strain and/or culture medium. These four strains showed different degrees of wheat root colonization. Fresh and dry weights, conductance, H2O2 content and antioxidant activities such as superoxide dismutase, peroxidase and catalase were analyzed, under optimal irrigation and water stress conditions, on 30-days-old wheat plants treated with four-day-old Trichoderma cultures, obtained from potato dextrose broth (PDB) and PDB-tryptophan (Trp). The application of Trichoderma PDB cultures to wheat plants could be linked to the plants’ ability to adapt the antioxidant machinery and to tolerate water stress. Plants treated with PDB cultures of T49 and T115 had the significantly highest weights under water stress. Compared to controls, treatments with strains T68 and T75, with constrained GA1 and GA4 production, resulted in smaller plants regardless of fungal growth medium and irrigation regime.

Changes in physiology, gene expression and ethylene biosynthesis in MDMV-infected sweet corn primed by small RNA pre-treatment.

The physiological condition of plants is significantly affected by viral infections. Viral proliferation occurs at the expense of the energy and protein stores in infected plant cells. At the same time, plants invest much of their remaining resources in the fight against infection, making them even less capable of normal growth processes. Thus, the slowdown in the development and growth processes of plants leads to a large-scale decrease in plant biomass and yields, which may be a perceptible problem even at the level of the national economy. One form of protection against viral infections is treatment with small interfering RNA (siRNA) molecules, which can directly reduce the amount of virus that multiplies in plant cells by enhancing the process of highly conserved RNA interference in plants. The present work demonstrated how pre-treatment with siRNA may provide protection against MDMV (Maize dwarf mosaic virus) infection in sweet corn (Zea mays cv. saccharata var. Honey Koern). In addition to monitoring the physiological condition of the maize plants, the accumulation of the virus in young leaves was examined, parallel, with changes in the plant RNA interference system and the ethylene (ET) biosynthetic pathway. The siRNA pre-treatment activated the plant antiviral defence system, thus significantly reducing viral RNA and coat protein levels in the youngest leaves of the plants. The lower initial amount of virus meant a weaker stress load, which allowed the plants to devote more energy to their growth and development. In contrast, small RNA pre-treatment did not initially have a significant effect on the ET biosynthetic pathway, but later a significant decrease was observed both in the level of transcription of genes responsible for ET production and, in the amount of ACC (1-aminocyclopropane-1-carboxylic acid) metabolite. The significantly better physiological condition, enhanced RNAi response and lower quantity of virus particles in siRNA pretreated plants, suggested that siRNA pre-treatment stimulated the antiviral defence mechanisms in MDMV infected plants. In addition, the consistently lower ACC content of the plants pre-treated with siRNA suggest that ET does not significantly contribute to the successful defence in this maize hybrid type against MDMV.

Dissecting the influence of the orchard location and the maturity at harvest on apple quality, physiology and susceptibility to major postharvest pathogens

‘Golden Reinders’ apple quality parameters, fruit physiology, biochemical composition and susceptibility to Penicillium expansum and Rhizopus stolonifer were analysed in fruit harvested from four different locations (two valley and two mountain orchards) and from the same valley orchard at six different maturity stages. Growing location strongly influenced the taste- and health-related fruit composition whereas the fruit maturity at harvest mainly affected the ethylene biosynthetic pathway and ethylene-dependant quality traits such as the fruit firmness and starch index. The fruit maturity at harvest, but not the growing location, also affected the severity of the infection caused by P. expansum and R. stolonifer, with mature fruit showing higher susceptibility to pathogen infection. Besides, by employing a Partial Least Square (PLS) regression model, our data showed that the severity of the lesions caused by R. stolonifer were intimately related to the fruit ethylene production. Overall, the results from this study demonstrate that differences in environmental conditions between orchards (mountain vs valley) strongly influenced the composition of ‘Golden Reinders’ apples without affecting the susceptibility of the fruit to two major postharvest pathogens.

Unravelling the cold-induced regulation of ethylene and α-farnesene and its involvement with the development of scald-like disorders in different pear cultivars

To better understand the cold-induced regulation of scald-like disorders in pears and the specific roles played by ethylene and α-farnesene, three pear cultivars with different patterns of ethylene production and chilling requirement were used in this study. Fruit were treated with 1-MCP (ethylene inhibitor) and Lovastatin (α-farnesene inhibitor) and stored at -0.5 °C and 90 % RH during 6 months. Changes in targeted metabolites, enzymes and genes were monitored periodically up to 120 d of storage and superficial scald incidence was assessed after this time and after 180 d of cold storage. 1-MCP treatment induced in the three cultivars a down-regulation of PcACS1, PcACO1, PcERF1 and PcAFS1 gene expression, but also a significant up-regulation of PcETR1 and PcEIN2 that led in all cases to the inhibition of the disorder incidence. In contrast, Lovastatin treatment caused diverse molecular or biochemical responses depending on the cultivar. In ‘Blanquilla’ pears, this treatment completely inhibited superficial scald reinforcing the idea that ethylene-α-farnesene interaction plays a decisive role in this specific cultivar. In contrast to 1-MCP, Lovastatin treatment did not control the disorder incidence in ‘Flor d’Hivern’ pears. Inversely, 1-MCP inhibited the development of the disorder, showing then that the inhibition of ethylene biosynthetic and signalling pathway may control superficial scald even in cultivars producing very low or undetectable ethylene levels. Finally, the inefficacy of both treatments to prevent the disorder development in ‘Conference’ pears, suggests the existence of a disorder different from that observed for the other cultivars whose biochemical basis remain unknown. Collectively our results show that the regulatory processes triggered by cold stress in pears are complex and cultivar dependent.

Assessment of the Germination Potential of Brassica oleracea Seeds Treated with Karrikin 1 and Cyanide, Which Modify the Ethylene Biosynthetic Pathway

The relationship between ethylene and cyanide (HCN) and karrikin 1 (KAR1) in dormancy release was studied in secondary dormant Brassica oleracea L. (Chinese cabbage) seeds. Freshly harvested seeds of Brassica oleracea usually have poor germination potential. Karrikin1 (KAR1) and cyanide (HCN) are able to stimulate seed germination. However, the stimulatory effects of these two chemicals depend on the activation of the ethylene biosynthesis pathway and on ethylene perception. In this study, KAR1 and HCN application increased the activity of ethylene and of two ethylene biosynthesis enzymes, ACC synthase (ACS) and ACC oxidase (ACO). KAR1 and HCN collectively promoted the accumulation of 1 aminocyclopropane-1-carboxylic acid (ACC). In the presence of NO (nitric oxide) and KAR1, ACS and ACO activities reached their maximum levels after 36 and 42 h, respectively. Ethylene inhibitors suppressed seed germination by approximately 55%, whereas the respiratory inhibitors SHAM and NaN3 inhibited seed germination by 5–10% in the presence of HCN and KAR1. KAR1 and HCN collectively reduced the abscisic acid (ABA) content in seeds, increased the gibberellic acid (GA) content and released seed dormancy. The expression of ethylene biosynthesis genes and ethylene receptor genes (BOACO1, BOACS1, BOACS3, BOACS4, BOACS5, BOACS7, BOACS9, BOACS11, BOETR1 and BOETR2) provided further evidence of the involvement of ethylene in KAR1 and HCN-induced germination. BOACO1, BOACS1, BOACS5, BOACS7, BOACS9, BOACS11, BOETR1 and BOETR2 genes were up regulated in the presence of KAR1 and HCN, while the remaining genes were down regulated. The expression of various ethylene biosynthesis and ethylene receptor genes suggested functional diversification and variations in seed sensitivity in the presence of KAR1 and HCN. Therefore, in the current study, KAR1 and HCN application effectively induced the germination of B. oleracea seeds (approximately 97% germination rate) after 6 days by modifying the ethylene biosynthetic pathway.

Alleviating dormancy in Brassica oleracea seeds using NO and KAR1 with ethylene biosynthetic pathway, ROS and antioxidant enzymes modifications

BackgroundSeed dormancy is a prevailing condition in which seeds are unable to germinate, even under favorable environmental conditions. Harvested Brassica oleracea (Chinese cabbage) seeds are dormant and normally germinate (poorly) at 21 °C. This study investigated the connections between ethylene, nitric oxide (NO), and karrikin 1 (KAR1) in the dormancy release of secondary dormant Brassica oleracea seeds.ResultsNO and KAR1 were found to induce seed germination, and stimulated the production of ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC), and both ethylene biosynthesis enzyme ACC oxidase (ACO) [1] and ACC synthase (ACS) [2]. In the presence of NO and KAR1, ACS and ACO activity reached maximum levels after 36 and 48 h, respectively. The inhibitor of ethylene 2,5-norbornadiene (NBD) had an adverse effect on Brassica oleracea seed germination (inhibiting nearly 50% of germination) in the presence of NO and KAR1. The benefits from NO and KAR1 in the germination of secondary dormant Brassica oleracea seeds were also associated with a marked increase in reactive oxygen species (ROS) (H2O2 and O2˙ˉ) and antioxidant enzyme activity at early germination stages. Catalase (CAT) and glutathione reductase (GR) activity increased 2 d and 4 d, respectively, after treatment, while no significant changes were observed in superoxide dismutase (SOD) activity under NO and KAR1 applications. An increase in H2O2 and O2˙ˉ levels were observed during the entire incubation period, which increasing ethylene production in the presence of NO and KAR1. Abscisic acid (ABA) contents decreased and glutathione reductase (GA) contents increased in the presence of NO and KAR1. Gene expression studies were carried out with seven ethylene biosynthesis ACC synthases (ACS) genes, two ethylene receptors (ETR) genes and one ACO gene. Our results provide more evidence for the involvement of ethylene in inducing seed germination in the presence of NO and KAR1. Three out of seven ethylene biosynthesis genes (BOACS7, BOACS9 and BOACS11), two ethylene receptors (BOETR1 and BOETR2) and one ACO gene (BOACO1) were up-regulated in the presence of NO and KAR1.ConclusionConsequently, ACS activity, ACO activity and the expression of different ethylene related genes increased, modified the ROS level, antioxidant enzyme activity, and ethylene biosynthesis pathway and successfully removed (nearly 98%) of the seed dormancy of secondary dormant Brassica olereace seeds after 7 days of NO and KAR1 application.

Double-sided battle: The role of ethylene during Monilinia spp. infection in peach at different phenological stages

Controversy exists on whether ethylene is involved in determining fruit resistance or susceptibility against biotic stress. In this work, the hypothesis that ethylene biosynthesis in peaches at different phenological stages may be modulated by Monilinia spp. was tested. To achieve this, at 49 and 126 d after full bloom (DAFB), ethylene biosynthesis of healthy and infected ‘Merryl O'Henry’ peaches with three strains of Monilinia spp. (M. fructicola (CPMC6) and M. laxa (CPML11 and ML8L) that differ in terms of aggressiveness) was analysed at the biochemical and molecular level along the course of infection in fruit stored at 20 °C. At 49 DAFB, results evidenced that infected fruit showed inhibition of ethylene production in comparison with non-inoculated fruit, suggesting that the three Monilinia strains were somehow suppressing ethylene biosynthesis to modify fruit defences to successfully infect the host. On the contrary, at 126 DAFB ethylene production increased concomitantly with brown rot spread, and values for non-inoculated fruit were almost undetectable throughout storage at 20 °C. The expression of several target genes involved in the ethylene biosynthetic pathway confirmed that they were differentially expressed upon Monilinia infection, pointing to a strain-dependent regulation. Notably, Prunus persica 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) (PpACS) family was the most over-expressed over time, demonstrating a positive ethylene regulation, especially at 126 DAFB. At this phenological stage it was demonstrated the ability of Monilinia spp. to alter ethylene biosynthesis through PpACS1 and benefit from the consequences of an ethylene burst likely on cell wall softening. Overall, our results put forward that infection not only among different strains but also at each stage is achieved by different mechanisms, with ethylene being a key factor in determining peach resistance or susceptibility to brown rot.

The nitrilase PtNIT1 catabolizes herbivore-induced nitriles in Populus trichocarpa

BackgroundNitrilases are nitrile-converting enzymes commonly found within the plant kingdom that play diverse roles in nitrile detoxification, nitrogen recycling, and phytohormone biosynthesis. Although nitrilases are present in all higher plants, little is known about their function in trees. Upon herbivory, poplars produce considerable amounts of toxic nitriles such as benzyl cyanide, 2-methylbutyronitrile, and 3-methylbutyronitrile. In addition, as byproduct of the ethylene biosynthetic pathway upregulated in many plant species after herbivory, toxic β-cyanoalanine may accumulate in damaged poplar leaves. In this work, we studied the nitrilase gene family in Populus trichocarpa and investigated the potential role of the nitrilase PtNIT1 in the catabolism of herbivore-induced nitriles.ResultsA BLAST analysis revealed three putative nitrilase genes (PtNIT1, PtNIT2, PtNIT3) in the genome of P. trichocarpa. While PtNIT1 was expressed in poplar leaves and showed increased transcript accumulation after leaf herbivory, PtNIT2 and PtNIT3 appeared not to be expressed in undamaged or herbivore-damaged leaves. Recombinant PtNIT1 produced in Escherichia coli accepted biogenic nitriles such as β-cyanoalanine, benzyl cyanide, and indole-3-acetonitrile as substrates in vitro and converted them into the corresponding acids. In addition to this nitrilase activity, PtNIT1 showed nitrile hydratase activity towards β-cyanoalanine, resulting in the formation of the amino acid asparagine. The kinetic parameters of PtNIT1 suggest that the enzyme utilizes β-cyanoalanine and benzyl cyanide as substrates in vivo. Indeed, β-cyanoalanine and benzyl cyanide were found to accumulate in herbivore-damaged poplar leaves. The upregulation of ethylene biosynthesis genes after leaf herbivory indicates that herbivore-induced β-cyanoalanine accumulation is likely caused by ethylene formation.ConclusionsOur data suggest a role for PtNIT1 in the catabolism of herbivore-induced β-cyanoalanine and benzyl cyanide in poplar leaves.

DOXC-class 2-oxoglutarate-dependent dioxygenase in safflower: Gene characterization, transcript abundance, and correlation with flavonoids

DOXC is one of the 2-oxoglutarate-dependent dioxygenases (2OGDs) classes, which is involved in the biosynthesis of colorful flavonoids and plant hormones. Safflower (Carthamus tinctorius L.) is a commonly used plant with flavonoids. Herein, we focused on analyzing the characterization, transcript abundance, and correlation of DOXC-class 2OGDs in safflower with flavonoids for the first time. TBLASTN analysis showed that they were implicated in the biosynthetic pathway of ethylene (DOXC1 and DOXC2), indole-3-acetic acid (DOXC3, DOXC4, and DOXC5), flavonoids (DOXC6, DOXC7, and DOXC8), and scopolamine (DOXC9 and DOXC10). The transcript abundance of DOXC1, DOXC2, DOXC6, DOXC7, and DOXC10 response to methyl jasmonate (MeJA) in two safflower lines (orange-yellow-flowered safflower line with major quinochalcones and minor flavonols, white-flowered safflower line with major flavonols and without quinochalcones) had converse transcript level accumulation. Coexpression analyses displayed that the transcript level of DOXC1, DOXC2 and DOXC8 was positively correlated with hydroxysafflor yellow A, a major quinochalcone in orange-yellow-flowered safflower line. DOXC3, DOXC4, DOXC5, DOXC7, and DOXC9 displayed a marked positive correlation with kaempferol-3-O-β-D-glucoside, a main flavonols in white-flowered safflower line. The response models of DOXC3, DOXC4, DOXC5 and DOXC9 showed amazing similarity in different safflower line, but the correlations with flavonoids were actually quite distinct. In orange-yellow-flowered safflower line, they might be implicated in the rutinoside modification of kaempferol and quercetin, but their functions were different and diversity in white-flowered safflower line. In sum, ten DOXC-class 2OGDs from safflower displayed different sequence features. Simultaneously, their expression pattern in two safflower lines in response to MeJA treatment, as well as their correlation with flavonoids, was different. These results implied the diversification of DOXC-class 2OGDs is partly responsible for the diversity and complexity of specialized metabolites in different phenotypes and chemotypes of safflower lines.

Ethylene and Polyamines in Counteracting Heavy Metal Phytotoxicity: A Crosstalk Perspective

The increasing trend of addition of heavy metals (HMs) to agricultural lands has increased toxicities in plants leading to significant declines in crop productivity. HM toxicity includes alterations in physiological processes, metabolic activities and overall growth and development of plants. The stimulation of oxidative stress is among the common concerns of toxicity in plants at the cellular level. Plant growth hormones/growth regulators have been key signalling molecules in delivering responses to HMs. The important phytohormones, ethylene and polyamines (PAs), play significant roles in the regulation of various developmental processes and signalling networks in plants. Notably, ethylene and PAs are also involved directly or indirectly in a widespread range of abiotic stress responses and tolerance/adaptation. As ethylene and PA biosynthesis involves a common precursor, S-adenosylmethionine, the interplay between ethylene and PAs is suggested in responses of plants to HM stress. The present work emphasizes the roles of these two phytohormones in signalling and regulation of HMs stress in plants based on the recent available reports. This work (a) overviews biosynthesis and signalling of ethylene and PAs; (b) critically appraises the functions of ethylene and PA, and the role of their promoters in HM-exposed plants; and (c) discusses crosstalk on the major mechanisms potentially governing ethylene and PA for plant HM-tolerance/adaptation. HMs in the appraised herein literature exhibited a differential modulation of PAs and ethylene biosynthetic pathways. In particular, the synergism between the PA and ethylene biosynthesis components could be helpful for plants in improving the ratio of root to shoot, increasing water (nutrients) uptake, modulating major signalling compounds, and thereby maintaining optimum cellular metabolism under HM stress.