Ethylene Synthesis Inhibitor Research Articles

Ethylene, a Signaling Compound Involved in Seed Germination and Dormancy.

The present review is focused on current findings on the involvement of ethylene in seed biology. The responsiveness of seeds to ethylene depends on the species and the dormancy status, improving concentrations ranging from 0.1 to 200 μL L-1. The signaling pathway of ethylene starts with its binding to five membrane-anchored receptors, which results in the deactivation of Constitutive Triple Response 1 (CTR1, a protein kinase) that does not exert its inhibitory effect on Ethylene Insensitive 2 (EIN2) by phosphorylating its cytosolic C-terminal domain. An analysis of germination in the presence of inhibitors of ethylene synthesis or action, and using seeds from mutant lines altered in terms of the genes involved in ethylene synthesis (acs) and the signaling pathway (etr1, ein2, ein4, ctr1 and erf1), demonstrates the involvement of ethylene in the regulation of seed dormancy. The promoting effect of ethylene is also regulated through crosstalk with abscisic acid (ABA) and gibberellins (GAs), essential hormones involved in seed germination and dormancy, and Reactive Oxygen Species (ROS). Using a mutant of the proteolytic N-degron pathway, Proteolysis (PRT6), the Ethylene Response Factors (ERFs) from group VII (HRE1, HRE2, RAP 2.2, RAP2.3 and RAP 2.12) have also been identified as being involved in seed insensitivity to ethylene. This review highlights the key roles of EIN2 and EIN3 in the ethylene signaling pathway and in interactions with different hormones and discusses the responsiveness of seeds to ethylene, depending on the species and the dormancy status.

Effect of aminoethoxyvinylglycine addition on the floral bud opening of Ranunculus asiaticus L cultivars

Objective: To evaluate the effect of aminoethoxyvinylglycine (AVG) additions on several growth variables of R. asiaticus in a greenhouse under a typically dry environment of the Mexicali valley.
 Design/methodology/approach: The variables determined were, bud opening rate, flower diameter, height of stem and bud growing rate and completely randomized block experimental design under a 2 by 4 factorial arrangement and three replicates was used for setting up the treatments with rates AVG of 0,100,150 and 200ppm over La Belle Deep Rose (DER) and La Belle Dark Orange (DAR) R. asiaticus cultivars.
 Results: The optimal dose of AVG for reducing flower bud diameter on both cultivars were those of 200 and 100 ppm respectively. Also, AVG addition had a significant effect in reducing stem height and growing rate for both cultivars.
 Limitations on study/implications: The use of AVG has shown good results as inhibitor of ethylene synthesis and extension of shelf life in carnations, snap dragons (Antirrhinum), ripening of fruits, and to reduce abortion of female flowers in certain species of walnuts, so, based on the above and considering the lack of information regarding the use of AVG inhibitor in the opening of Persian Buttercup flower buds was used AVG in R. asiaticus.
 Findings/conclusions: AVG addition on plants of R. asiaticus had a significant effect reducing growth, both in diameter and height in the La Belle Deep Rose (DER) and La Belle Dark Orange (DAR) varieties

Ethylene and ROS mediate root growth inhibition induced by the endocrine disruptor bisphenol A (BPA)

Bisphenol A (BPA) functions as a detrimental substance that disrupts the endocrine system in animals while also impeding the growth and development of plants. In our previous study, we demonstrated that BPA hinders the growth of roots in Arabidopsis by diminishing cell division and elongation, which is ascribed to the increased accumulation and redistribution of auxin. Here, we examined the mediation of ROS and ethylene in BPA-induced auxin accumulation and root growth inhibition. BPA enhanced ROS levels, and ROS increased auxin contents but reduced cell division activity and the expression of EXPA8 involved in root elongation. ROS scavenger treatment reversed BPA-triggered root growth retardation, auxin accumulation, and cell division inhibition. In addition, BPA induced ethylene, and ethylene synthesis inhibitor treatment reversed BPA-triggered root growth retardation and auxin accumulation. Taken together, ROS and ethylene are involved in BPA-inhibited cell elongation and cell division by mediating auxin accumulation and redistribution.

Application of ethylene synthesis inhibitor in arabica coffee on field infestation, preference, and performance of Hypothenemus hampei

Application of ethylene synthesis inhibitor in arabica coffee on field infestation, preference, and performance of Hypothenemus hampei

Ethylene Regulates Combined Drought and Low Nitrogen Tolerance in Wheat: Proteomic Analysis

Wheat is a staple crop in China’s arid and semi-arid regions. Drought and low nitrogen (LN) are two major constraints to wheat growth and production. However, the molecular mechanism underlying wheat response to both drought and LN stress remains unknown. Accordingly, we conducted a proteomic study on the roots of two wheat varieties, Chang6878 (drought tolerant) and Shi4185 (drought sensitive) and compared the differences between drought and combined drought and LN stress treatments. In total, 5143 proteins were identified, of which 163 differentially abundant proteins (DAPs) were uniquely upregulated under drought and LN stress in Chang6878. Enrichment analysis showed that DAPs were mainly involved in mitogen-activated protein kinase signaling, phenylpropanoid biosynthesis, glutathione metabolism, ethylene biosynthesis, ethylene signal transduction, and oxidation–reduction reactions. These DAPs were verified via parallel reaction monitoring and quantitative real-time polymerase chain reaction. Chang6878 was treated with the ethylene synthesis precursor 1-aminocyclopropanecarboxylic acid, and its resistance to drought and LN stress improved. After treatment with the ethylene synthesis inhibitor silver nitrate and ethylene signal transduction inhibitor 1-methylcyclopropene, drought and LN stress resistance reduced. These results provide novel insights into the tolerance mechanisms of Chang6878 to drought and LN stress by altering ethylene synthesis and signal transduction. This study provides a reference for breeding drought- and low-nitrogen-tolerant wheat germplasm resources and a theoretical basis for maintaining food security in arid, barren areas.

TARGET OF EAT3 (TOE3) specifically regulates fruit spine initiation in cucumber (Cucumis sativus L.).

The presence or absence of spines is an important economic trait of cucumber fruit. Spines are believed to be a type of specialized trichome on the fruit surface and all the identified cucumber trichome-less mutants lack fruit spines. However, genes that specifically regulate fruit spine initiation remain to be identified. Here, we found that knocking out cucumber TARGET OF EAT3 homolog (CsTOE3), belonging to the APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) family, affected flower development, and more interestingly, inhibited cucumber fruit spine initiation. On analyzing expression patterns by qRT-PCR and in situ hybridization assay, CsTOE3 was found to be highly expressed in male and female flowers, and its mRNA accumulated in the tips of sepal and petal primordia and in the cells of fruit spines and peels. Biochemical analyses indicated that CsTOE3 directly interacts with GLABRA1 (CsGL1) and TRANSPARENT TESTA GLABRA1 (CsTTG1), which are positive regulators of trichome formation. In addition, RNA-seq showed that the transcription levels of eight ERFs were significantly upregulated in CsTOE3 knockout lines. Phytohormone content analysis also revealed a significant increase in the amount of ethylene released by CsTOE3 knockout lines; treatment with the ethylene synthesis inhibitor aminoethoxyvinyl-glycine (AVG) partly restored the spineless phenotype. Our results suggest that CsTOE3 specifically regulates fruit spine initiation but does not affect the formation of trichomes on other organs in cucumber. Our findings may have a far-reaching significance for cucumber germplasm improvement and quality breeding using fruit spines as the target trait.

Dissecting the effect of ethylene in the transcriptional regulation of chilling treatment in grapevine leaves

Ethylene (ETH) plays important roles in various development programs and stress responses in plants. In grapevines, ETH increased dramatically under chilling stress and is known to positively regulate cold tolerance. However, the role of ETH in transcriptional regulation during chilling stress of grapevine leaves is still not clear. To address this gap, targeted hormone profiling and transcriptomic analysis were performed on leaves of Vitis amurensis under chilling stress with and without aminoethoxyvinylglycine (AVG, a inhibitor of ETH synthesis) treatment. APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) and WRKY transcription factors (TF) were only the two highly enriched TF families that were consistently up-regulated during chilling stress but inhibited by AVG. The comparison of leaf transcriptomes between chilling treatment and chilling with AVG allowed the identification of potential ETH-regulated genes. Potential genes that are positively regulated by ETH are enriched in solute transport, protein biosynthesis, phytohormone action, antioxidant and carbohydrate metabolism. Conversely, genes related to the synthesis and signaling of ETH, indole-3-acetic acid (IAA), abscisic acid (ABA) were up-regulated by chilling treatment but inhibited by AVG. The contents of ETH, ABA and IAA also paralleled with the transcriptome data, which suggests that the response of ABA and IAA during chilling stress may regulate by ETH signaling, and together may belong to an integrated network of hormonal signaling pathways underpinning chilling stress response in grapevine leaves. Together, these findings provide new clues for further studying the complex regulatory mechanism of ETH under low-temperature stress in plants more generally and new opportunities for breeding cold-resilient grapevines.

Grain filling in rice vis‐a‐vis ethylene production in the spikelets

AbstractRice being a staple food worldwide necessitates that its production be enhanced to meet the demands of the continuously increasing population. However, the productivity advantages associated with breeding programs have reached their maximum. The production plateau brought on is not due to a lack of genetic potential but rather is due to the inhibition of grain filling by ethylene produced in large quantities in the heavy‐panicle‐ and compact‐panicle‐type varieties developed thus far, as evidenced by the application of ethylene synthesis inhibitors and ethylene action blockers. The inhibition could be a result of the accumulation of HCN, a byproduct of ethylene biosynthesis. In addition, inhibition of grain filling by excessive amounts of ethylene may also be the result of enhanced synthesis/expression of rice starch regulator 1, an ethylene‐responsive element binding protein that inhibits expression of the genes encoding type I starch‐biosynthesizing enzymes. In the past decade, miRNAs have also been found to inhibit grain filling by targeting starch‐biosynthesizing enzymes and the transcription factors required for their expression. Hence, biotechnological interventions should be designed to (1) decrease ethylene production and CN− accumulation and (2) downregulate/knockdown the expression of miRNAs unfavorable to grain filling in a spikelet/seed‐specific manner to enhance rice production.

Endophytic yeast protect plants against metal toxicity by inhibiting plant metal uptake through an ethylene-dependent mechanism.

Toxic metal pollution requires significant adjustments in plant metabolism. Here, we show that the plant microbiota plays an important role in this process. The endophytic Sporobolomyces ruberrimus isolated from a serpentine population of Arabidopsis arenosa protected plants against excess metals. Coculture with its native host and Arabidopsis thaliana inhibited Fe and Ni uptake. It had no effect on host Zn and Cd uptake. Fe uptake inhibition was confirmed in wheat and rape. Our investigations show that, for the metal inhibitory effect, the interference of microorganisms in plant ethylene homeostasis is necessary. Application of an ethylene synthesis inhibitor, as well as loss-of-function mutations in canonical ethylene signalling genes, prevented metal uptake inhibition by the fungus. Coculture with S. ruberrimus significantly changed the expression of Fe homeostasis genes: IRT1, OPT3, OPT6, bHLH38 and bHLH39 in wild-type (WT) A. thaliana. The expression pattern of these genes in WT plants and in the ethylene signalling defective mutants significantly differed and coincided with the plant accumulation phenotype. Most notably, down-regulation of the expression of IRT1 solely in WT was necessary for the inhibition of metal uptake in plants. This study shows that microorganisms optimize plant Fe and Ni uptake by fine-tuning plant metal homeostasis.

Silver nitrate reduces hyperhydricity in shoots regenerated from the hypocotyl of snapdragon cv. Maryland Apple Blossom

We developed an efficient protocol for shoot regeneration from hypocotyl explants in snapdragon (Antirrhinum majus L.) cv. Maryand Apple Blossom by plant growth regulators (PGRs), followed by ethylene synthesis inhibitor Aminoethoxyvinylglycine (AVG), ethylene precursor 1-Aminocyclopropane-1-carboxylate (ACC), and ethylene action inhibitor silver nitrate (AgNO3). The combination of benzyladenine (BA) and 2,4-dichlorophenoxyacetic acid (2,4-D) did not induce shoots, whereas naphthaleneacetic acid (NAA) and Zeatin (Zt) induced shoots. The combination of 0.05 mg/L NAA and 2.5 mg/L Zt resulted in the maximum shoot regeneration percentage and a reasonable number of shoots per explant. However, the regenerated shoots exhibited hyperhydricity and failed to develop into normal plants when introduced into plant growth media. Addition of ACC and AVG to the media containing 0.05 mg/L NAA and 2.5 mg/L Zt inhibited shoot regeneration, while AgNO3 (2.0 mg/L) marginally improved shoot regeneration and successfully reduced hyperhydricity. Shoots grown in AgNO3-containing media showed a reduction in ethylene related gene expression and reactive oxygen species (ROS) accumulation; the leaves showed reduced intercellular space as well as an increase in the number of open stomata under AgNO3 treatment. Moreover, shoots regenerated from AgNO3-containing media easily developed into normal plants in plant growth medium. This study highlights the importance of specific PGRs in shoot regeneration, as well as the role of AgNO3 in reducing the hyperhydricity of shoots regenerated in vitro. These findings will contribute to a better understanding of the hyperhydricity mechanism. We expect this protocol to be useful for in vitro shoot regeneration and genetic transformation of the snapdragon cultivar used in this study.

Design of aminoethoxyvinylglycine functional analogues to delay postharvest ripening of tomato fruit

Ethylene is a key hormone in regulating fruit ripening, thus inhibiting ethylene production is an effective way to delay postharvest ripening of fruit. Aminoethoxyvinylglycine (AVG) is a competitively ethylene synthesis inhibitor that can significantly delay the fruit softening at postharvest stage and prolong the fruit shelf life. However, the high production cost of AVG limits its widespread use. In this study, nine AVG analogues with simple structures were designed and synthesized based on the 1-aminocyclo-propane-1-carboxylic acid synthase (ACS) enzyme ACS2 (Protein Data Bank ID: 1AIY) of tomato. The molecular docking analysis of ACS2 with AVG analogues showed that the compounds 2i, 2k, and 2 n have higher predicted binding activity than the other analogues, which form hydrogen bonds with the key amino acids Ala54 and Arg412 of ACS2. Compounds 2i, 2k, and 2 n reduce ethylene production and delay the postharvest ripening of tomato fruit in varying degrees, and 2 n is the most effective AVG analogue, suggesting that the function of these analogues is basically associated with their predicted binding activity with ACS2. This study developed a new class of ethylene synthesis inhibitors with significant effects on the control of ethylene action and prolonging fruit shelf life. This work also has crucial implications for research on structure-activity relationship and development of more potential AVG functional analogues.

Polyamines and ethylene interact in mediating the effect of nitrogen rates on synthesis of amino acids in rice grains

AbstractNitrogen (N) is one of the essential factors influencing amino acid synthesis in rice (Oryza sativa L.) grains. Polyamines (PAs) and ethylene (ETH) play vital roles in grain amino acid biosynthesis of rice. However, knowledge is limited about whether and how PAs and ETH mediate the effect of N rate on amino acid biosynthesis. Two rice cultivars were used with three N rates of low (LN), medium (MN), and high (HN) in the study. Levels of free PAs and ETH, activities/gene expressions of key enzymes related to amino acid synthesis in grains, and the amino acid contents in milled rice were investigated. Free spermidine (Spd) and spermine (Spm) concentrations, especially ratios of free PAs to 1‐aminocylopropane‐1‐carboxylic acid (ACC), and total amino acids (TAAs), essential amino acids (EAAs), and non‐essential amino acids (NEAAs) contents were increased with N rate, while ethylene evolution rate (EER) and ACC concentration were reduced with N increases. There was relatively little difference in the above parameters between MN and HN. Levels of free Spd and Spm, and their ratios to ACC exhibited significant and positive correlations with the activities/gene expressions of key enzymes related to amino acid biosynthesis, and TAAs, NEAAs, and EAAs contents, whereas ACC and EER levels had significantly negative correlations with those parameters. Exogenous Spd, Spm, or AVG (an ETH synthesis inhibitor) increased the enzymatic activities and gene expressions, whereas MGBG (a Spd or Spm synthesis inhibitor) or ethephon (an ETH‐releasing agent) exerted the opposite effect. These results demonstrated that free PAs and ETH antagonistically interact in mediating the effect of N rate on grain amino acid synthesis of rice. Higher ratios of free PAs to ACC could promote synthesis of amino acids in grains of rice.

Ethylene works as a possible regulator for the rootlet elongation and transcription of genes for phosphorus acquisition in cluster roots of Lupinus albus L.

ABSTRACT White lupin (Lupinus albus L.) plants are tolerant plants under phosphorus (P)deficiency. They form unique morphological roots, so-called cluster roots (CRs) under P deficiency. CRs contribute to P absorption by the expansion of the root surface area and P mobilization activities. Previous research has implied the involvement of several hormonal functions in CR formation. Ethylene is a key regulator responsible for the modification of root architecture and P acquisition in response to low P in plants. However, understanding the effect of ethylene on CR morphogenesis is not enough. Here, the focus was on the effects of ethylene on CR morphology and gene expression for P acquisition. First, a reanalysis of public RNA-Seq data indicated that the gene expression for ethylene synthesis was induced during CR maturation. In turn, the 10-days application of an ethylene synthesis inhibitor, CoCl2, and an ethylene precursor, ACC, to CR formed in hydroponic culture without P was performed. CR morphology, transcript levels of the genes related to P acquisition, and citrate concentration in roots were determined. The results indicated that the elongation of rootlets in CR was promoted in a Co2+ concentration-dependent manner, suggesting that ethylene is responsible for the arrest of rootlet elongation. mRNA accumulation for acid phosphatases, phosphate transporters, citrate synthases, and a putative citrate transporter increased in ACC-treated immature CR, suggesting that ethylene induces the transcription of genes for P acquisition. Additionally, the trend of citrate concentration in roots among treatments was similar to that in the expression of citrate synthases, supporting that ethylene accumulation promotes citrate synthesis. The roles of the arrest of rootlet elongation and regulation of gene expressions for P acquisition are considered independent functions of ethylene. It was concluded that ethylene works as a possible regulator for the rootlet elongation and transcription of genes for P acquisition in CRs, although further studies are required to elucidate the molecular mechanisms of the arrest of rootlet elongation and transcriptional regulation.

Salicylic Acid Enhances Adventitious Root and Aerenchyma Formation in Wheat under Waterlogged Conditions.

The present study investigated the role of salicylic acid (SA) in regulating morpho-anatomical adaptive responses of a wheat plant to waterlogging. Our pharmacological study showed that treatment of waterlogged wheat plants with exogenous SA promotes the formation axile roots and surface adventitious roots that originate from basal stem nodes, but inhibits their elongation, leading to the formation of a shallow root system. The treatment also enhanced axile root formation in non-waterlogged plants but with only slight reductions in their length and branch root formation. Exogenous SA enhanced the formation of root aerenchyma, a key anatomical adaptive response of plants to waterlogging. Consistent with these results, waterlogging enhanced SA content in the root via expression of specific isochorismate synthase (ICS; ICS1 and ICS2) and phenylalanine ammonia lyase (PAL; PAL4, PAL5 and PAL6) genes and in the stem nodes via expression of specific PAL (PAL5 and PAL6) genes. Although not to the same level observed in waterlogged plants, exogenous SA also induced aerenchyma formation in non-waterlogged plants. The findings of this study furthermore indicated that inhibition of ethylene synthesis in SA treated non-waterlogged and waterlogged plants does not have any effect on SA-induced emergence of axile and/or surface adventitious roots but represses SA-mediated induction of aerenchyma formation. These results highlight that the role of SA in promoting the development of axile and surface adventitious roots in waterlogged wheat plants is ethylene independent while the induction of aerenchyma formation by SA requires the presence of ethylene.

Effects of 1-methylcyclopropene and gaseous ozone on Listeria innocua survival and fruit quality of Granny Smith apples during long-term commercial cold storage

This study evaluated the impact of 1-methylcyclopropene (1-MCP), an ethylene synthesis inhibitor, followed by long-term commercial cold storage with low-dose gaseous ozone on the microbiological safety and quality of fresh apples. Granny Smith apples were inoculated with or without Listeria innocua, treated with or without 1.0 mg/L 1-MCP for 24 h, then subjected to commercial cold storage conditions including refrigerated air (RA, 0.6 °C, control), controlled atmosphere (CA, 2% O2, 1% CO2, 0.6 °C), and CA with 51–87 μg/L ozone gas for up to 36 weeks. RA storage reduced L. innocua on apples by up to 3.6 log10 CFU/apple. CA had no advantage over RA in controlling Listeria. Continuous ozone gas application resulted in an additional ∼2.0 log10 CFU/apple reduction of L. innocua (total reduction up to 5.7 log10 CFU/apple) and suppressed native bacteria and fungi. Treatment with 1-MCP had a minor impact on survival of L. innocua or background microbiota on apples, while it significantly delayed fruit ripening and reduced the incidence of superficial scald and internal browning. In summary, 1-MCP treatment followed by CA storage with low-dose continuous ozone gas can effectively control Listeria on fresh apples and delay fruit ripening.

Preharvest fumigation of 1-Methylcyclopropene, aminoethoxyvin-ylglycine, chlorine dioxide and nitric oxide for improving postharvest quality of durian (Durio zibethinus) fruit

1-Methylcyclopropene, aminoethoxyvinylglycine, chlorine dioxide and nitric oxide were widely applied as ethylene synthesis inhibitors for crops at pre-harvest stages for various purposes. Durian (Durio zibethinus) was a seasonal fruit commonly cultivated in tropical regions. Durian was highly perishable at ambient condition due to its high respiration rate and ethylene accumulation. Preharvest treatment was considered as a promising strategy to regulate some physiological behaviors of durian during postharvest storage. This research was conducted during 2020 at Soc Trang Nanotech laboratory, Vietnam to evaluate the effectiveness of preharvest fumigation at dose 200 μL/L at 14 days before harvesting with 1-Methylcyclopropene (1-MCP), aminoethoxyvinylglycine (AVG), chlorine dioxide (ClO2) and nitric oxide (NO) on quality of durian fruit. After harvesting, the treated fruits were kept at 4°C for 28 days. In 7 day-interval, sample was taken to evaluate respiration rate, ascorbic acid content, glutathione content and ascorbic peroxidase activity. Results showed that 1-MCP-treated durian had the lowest respiration rate (101.24±1.27 mg CO2/kg/h) while maintained the highest ascorbic acid content (21.73±0.22 mg/100 g), glutathione content (29.30±0.11 μmol/kg) and ascorbic peroxidase activity (2.31±0.02 U/g) at the end of 28 days of storage. Preharvest treatment by 1-MCP significantly enhanced quality of durian fruit in an extended stability.

Differential effects of postharvest application of ethylene inhibitors on guava stored under ambient conditions

Aim: To assess the efficiency of ethylene synthesis and action inhibitors on postharvest shelf life of guava fruits under ambient conditions. Methodology: Mature green guava fruits (P. guajava L. cv. Arka Mridula) were harvested and treated with ethylene inhibitors. Various physiological, physical and nutritional changes of the treated fruits in comparison with untreated ones were monitored during ambient temperature storage. Multivariate analysis approach was used for interpreting the data on quality changes during storage. Results: Significant positive correlation (p<0.01) was observed among rates of ethylene production, respiration, ripening and Hunter’s a* value. Biplot from principal component analysis of eleven parameters showed that 1-MCP (500 ppb) treated fruits were grouped together with freshly harvested fruits throughout storage period, and proved superior over other treatments in delaying ripening and quality maintenance. Seven days stored 3.0 mM Salicylic acid and 1.5 mM Sodium nitroprusside treated fruits were grouped together with 5 days stored control fruits, suggesting their effectiveness in extending the shelf life by additional two days. Interpretation: Postharvest application of 1-MCP on guava fruits can extend the shelf life by four days when compared with control. Even PCA indicated that the study of major ripening attributes (L*, a*, b*, Hue, texture, acidity, ethylene rate and respiration rate) was quite sufficient to know the ripening status of the fruits.

Comparative Study of Several Fe Deficiency Responses in the Arabidopsis thaliana Ethylene Insensitive Mutants ein2-1 and ein2-5.

Iron (Fe) is an essential micronutrient for plants since it participates in essential processes such as photosynthesis, respiration and nitrogen assimilation. Fe is an abundant element in most soils, but its availability for plants is low, especially in calcareous soils. Fe deficiency causes Fe chlorosis, which can affect the productivity of the affected crops. Plants favor Fe acquisition by developing morphological and physiological responses in their roots. Ethylene (ET) and nitric oxide (NO) have been involved in the induction of Fe deficiency responses in dicot (Strategy I) plants, such as Arabidopsis. In this work, we have conducted a comparative study on the development of subapical root hairs, of the expression of the main Fe acquisition genes FRO2 and IRT1, and of the master transcription factor FIT, in two Arabidopsis thaliana ET insensitive mutants, ein2-1 and ein2-5, affected in EIN2, a critical component of the ET transduction pathway. The results obtained show that both mutants do not induce subapical root hairs either under Fe deficiency or upon treatments with the ET precursor 1-aminocyclopropane-1-carboxylate (ACC) and the NO donor S-nitrosoglutathione (GSNO). By contrast, both of them upregulate the Fe acquisition genes FRO2 and IRT1 (and FIT) under Fe deficiency. However, the upregulation was different when the mutants were exposed to ET [ACC and cobalt (Co), an ET synthesis inhibitor] and GSNO treatments. All these results clearly support the participation of ET and NO, through EIN2, in the regulation of subapical root hairs and Fe acquisition genes. The results will be discussed, taking into account the role of both ET and NO in the regulation of Fe deficiency responses.

Seed Transcriptome Annotation Reveals Enhanced Expression of Genes Related to ROS Homeostasis and Ethylene Metabolism at Alternating Temperatures in Wild Cardoon.

The association among environmental cues, ethylene response, ABA signaling, and reactive oxygen species (ROS) homeostasis in the process of seed dormancy release is nowadays well-established in many species. Alternating temperatures are recognized as one of the main environmental signals determining dormancy release, but their underlying mechanisms are scarcely known. Dry after-ripened wild cardoon achenes germinated poorly at a constant temperature of 20, 15, or 10 °C, whereas germination was stimulated by 80% at alternating temperatures of 20/10 °C. Using an RNA-Seq approach, we identified 23,640 and annotated 14,078 gene transcripts expressed in dry achenes and achenes exposed to constant or alternating temperatures. Transcriptional patterns identified in dry condition included seed reserve and response to dehydration stress genes (i.e., HSPs, peroxidases, and LEAs). At a constant temperature, we observed an upregulation of ABA biosynthesis genes (i.e., NCED9), ABA-responsive genes (i.e., ABI5 and TAP), as well as other genes previously related to physiological dormancy and inhibition of germination. However, the alternating temperatures were associated with the upregulation of ethylene metabolism (i.e., ACO1, 4, and ACS10) and signaling (i.e., EXPs) genes and ROS homeostasis regulators genes (i.e., RBOH and CAT). Accordingly, the ethylene production was twice as high at alternating than at constant temperatures. The presence in the germination medium of ethylene or ROS synthesis and signaling inhibitors reduced significantly, but not completely, germination at 20/10 °C. Conversely, the presence of methyl viologen and salicylhydroxamic acid (SHAM), a peroxidase inhibitor, partially increased germination at constant temperature. Taken together, the present study provides the first insights into the gene expression patterns and physiological response associated with dormancy release at alternating temperatures in wild cardoon (Cynara cardunculus var. sylvestris).

Transcriptomic and phosphoproteomic profiling and metabolite analyses reveal the mechanism of NaHCO3-induced organic acid secretion in grapevine roots

BackgroundOrganic acid secretion is a widespread physiological response of plants to alkalinity. However, the characteristics and underlying mechanism of the alkali-induced secretion of organic acids are poorly understood.ResultsOxalate was the main organic acid synthesized and secreted in grapevine (a hybrid of Vitis amurensis, V. berlandieri and V. riparia) roots, while acetate synthesis and malate secretion were also promoted under NaHCO3 stress. NaHCO3 stress enhanced the H+ efflux rate of grapevine roots, which is related to the plasma membrane H+-ATPase activity. Transcriptomic profiling revealed that carbohydrate metabolism was the most significantly altered biological process under NaHCO3 stress; a total of seven genes related to organic acid metabolism were significantly altered, including two phosphoenolpyruvate carboxylases and phosphoenolpyruvate carboxylase kinases. Additionally, the expression levels of five ATP-binding cassette transporters, particularly ATP-binding cassette B19, and two Al-activated malate transporter 2 s were substantially upregulated by NaHCO3 stress. Phosphoproteomic profiling demonstrated that the altered phosphoproteins were primarily related to binding, catalytic activity and transporter activity in the context of their molecular functions. The phosphorylation levels of phosphoenolpyruvate carboxylase 3, two plasma membrane H+-ATPases 4 and ATP-binding cassette B19 and pleiotropic drug resistance 12 were significantly increased. Additionally, the inhibition of ethylene synthesis and perception completely blocked NaHCO3-induced organic acid secretion, while the inhibition of indoleacetic acid synthesis reduced NaHCO3-induced organic acid secretion.ConclusionsOur results demonstrated that oxalate was the main organic acid produced under alkali stress and revealed the necessity of ethylene in mediating organic acid secretion. Additionally, we further identified several candidate genes and phosphoproteins responsible for organic acid metabolism and secretion.