ACC Synthase Research Articles

Nitric oxide is involved in the regulation of guard mother cell division by inhibiting the synthesis of ACC.

A stoma forms by a series of asymmetric divisions of stomatal lineage precursor cell and the terminal division of a guard mother cell (GMC). GMC division is restricted to once through genetic regulation mechanisms. Here, we show that nitric oxide (NO) is involved in the regulation of the GMC division. NO donor treatment results in the formation of single guard cells (SGCs). SGCs are also produced in plants that accumulate high NO, whereas clustered guard cells (GCs) appear in plants with low NO accumulation. NO treatment promotes the formation of SGCs in the stomatal signalling mutants sdd1, epf1 epf2, tmm1, erl1 erl2 and er erl1 erl2, reduces the cell number per stomatal cluster in the fama-1 and flp1 myb88, but has no effect on stomatal of cdkb1;1 cyca2;234. Aminocyclopropane-1-carboxylic acid (ACC), a positive regulator of GMC division, reduces the NO-induced SGC formation. Further investigation found NO inhibits ACC synthesis by repressing the expression of several ACC SYNTHASE (ACS) genes, and in turn ACC represses NO accumulation by promoting the expression of HEMOGLOBIN 1 (HB1) encoding a NO scavenger. This work shows NO plays a role in the regulation of GMC division by modulating ACC accumulation in the Arabidopsis cotyledon.

Application of nanoparticles blue-TiO2-x and chitosan coating to delay ripening and suppress ethylene-related gene expression of Cavendish banana

Cavendish bananas are climacteric fruits that rapidly respond to biochemical reactions during ripening. Therefore, it quickly undergoes a decrease in commercial value during post-harvest storage. This study evaluated the effect of Fruit Storage Chamber (FSC) modification on the photoactivation of nanoparticles blue-TiO2-x and 1.25 % (w/v) chitosan coatings on the physicochemical and molecular characteristics of Cavendish bananas stored at a low temperature (22 °C). The results showed that the combination of FSC treatment supplemented with nanoparticles blue-TiO2-x and bananas coated with 1.25 % (w/v) chitosan can maintain fruit quality during seven days of storage at 22 °C, compared to the control. Applying both of nanoparticles blue-TiO2-x variants with chitosan-coated bananas can suppress the relative expression of the MaACS1 gene until the 5th day but lead to an up-regulated expression on the following day. However, the control sample stored in FSC with nanoparticles blue-TiO2-x was the best treatment to suppress relative MaACS1 (Musa acuminata ACC synthase 1) and MaACO1 (Musa acuminata ACC Oxidase 1) gene expression in the pulp until the end of shelf life. It means the treated sample with 1.25 % chitosan could suppress MaACO1 gene expression six times more than a banana without chitosan while in storage without FSC. MaACO1 expression in nanoparticles blue-TiO2-x bananas coated with 1.25 % (w/v) chitosan decreased 28-fold during storage 7 days. This study suggested that a 1.25 % chitosan coating combined with storage in FSC with nanoparticles blue-TiO2-x can inhibit ACC oxidase from converting ACC to ethylene. This study demonstrated that an FSC equipped with nano-TiO2 variants, low temperature, and 1.25 % (w/v) chitosan coating is a promising solution that could delay ripening and extend the shelf life of Cavendish bananas.

Cytokinins regulate spatially specific ethylene production to control root growth in Arabidopsis

Two principal growth regulators, cytokinins and ethylene, are known to interact in the regulation of plant growth. However, information about the underlying molecular mechanism and positional specificity of cytokinin/ethylene crosstalk in the control of root growth is scarce. We have identified the spatial specificity of cytokinin-regulated root elongation and root apical meristem (RAM) size, both of which we demonstrate to be dependent on ethylene biosynthesis. Upregulation of the cytokinin biosynthetic gene ISOPENTENYLTRANSFERASE (IPT) in proximal and peripheral tissues leads to both root and RAM shortening. By contrast, IPT activation in distal and inner tissues reduces RAM size while leaving the root length comparable to that of mock-treated controls. We show that cytokinins regulate two steps specific to ethylene biosynthesis: production of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) by ACC SYNTHASEs (ACSs) and its conversion to ethylene by ACC OXIDASEs (ACOs). We describe cytokinin- and ethylene-specific regulation controlling the activity of ACSs and ACOs that are spatially discrete along both proximo/distal and radial root axes. Using direct ethylene measurements, we identify ACO2, ACO3, and ACO4 as being responsible for ethylene biosynthesis and ethylene-regulated root and RAM shortening in cytokinin-treated Arabidopsis. Direct interaction between ARABIDOPSIS RESPONSE REGULATOR 2 (ARR2), a member of the multistep phosphorelay cascade, and the C-terminal portion of ETHYLENE INSENSITIVE 2 (EIN2-C), a key regulator of canonical ethylene signaling, is involved in the cytokinin-induced, ethylene-mediated control of ACO4. We propose tight cooperation between cytokinin and ethylene signaling in the spatially specific regulation of ethylene biosynthesis as a key aspect of the hormonal control of root growth.

Impairment in a member of AP2/ERF and F-box family protein enhances complete panicle exsertion in rice.

Complete panicle exsertion (CPE) is an economically important quantitative trait that contributes to grain yield in rice. We deployed an integrated approach for understanding the molecular mechanism of CPE using a stable ethyl methanesulfonate mutant line, CPE-109 of the Samba Mahsuri (SM) variety of rice (Oryza sativa), which exhibits CPE. Two consistent genomic regions were identified for CPE through quantitative trait locus (QTL) mapping [qCPE-4 (28.24-31.22 Mb) and qCPE-12 (2.30-3.18 Mb)] and QTL-sequencing [chr 4 (31.21-33.69 Mb) and chr 12 (0.12-3.15 Mb)]. Two non-synonymous single nucleotide polymorphisms, namely KASP 12-12 (T→C; chr12:1269983) in Os12g0126300, encoding an AP2/ERF transcription factor, and KASP 12-16 (G→A; chr12:1515198) in Os12g0131400, encoding an F-box domain-containing protein, explained 81.05% and 59.61% of the phenotypic variance, respectively, and exhibited strong co-segregation with CPE in F2 mapping populations, advanced generation lines, and CPE-exhibiting SM mutants through KASP assays. Down-regulation of these genes in CPE-109 compared with SM (wild type) was observed in transcriptome sequencing of flag leaves, which was validated through qRT-PCR. We propose that the abrogation of Os12g0126300 and Os12g0131400 in CPE-109 combinatorially influences down-regulation of ethylene biosynthetic genes, Os01g0192900 (ACC synthase) and Os05g0497300 (ethylene-responsive factor-2), and up-regulation of a gibberellic acid synthetic gene, Os06g0569900 (ent-kaurene synthase) and the two cytokinin biosynthetic genes Os07g0486700 (cytokinin-O-glucosyltransferase 2) and Os10g0479500 (similar to carboxy-lyase), which results in complete panicle exsertion.

AVG Treatment at Pre-harvest to Delay Ripeness on Booth7 Avocado Based on the Activity of ACC Synthases and ACC Oxidase Enzymes

AVG Treatment at Pre-harvest to Delay Ripeness on Booth7 Avocado Based on the Activity of ACC Synthases and ACC Oxidase Enzymes

Identification of Key Ubiquitination Sites Involved in the Proteasomal Degradation of AtACS7 in Arabidopsis.

The gaseous hormone ethylene plays pivotal roles in plant growth and development. The rate-limiting enzyme of ethylene biosynthesis in seed plants is 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS). ACS proteins are encoded by a multigene family and the expression of ACS genes is highly regulated, especially at a post-translational level. AtACS7, the only type III ACS in Arabidopsis, is degraded in a 26S proteasome-dependent pathway. Here, by using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) analysis, two lysine residues of AtACS7, lys285 (K285) and lys366 (K366), were revealed to be ubiquitin-modified in young, light-grown Arabidopsis seedlings but not in etiolated seedlings. Deubiquitylation-mimicking mutations of these residues significantly increased the stability of the AtACS7K285RK366R mutant protein in cell-free degradation assays. All results suggest that K285 and K366 are the major ubiquitination sites on AtACS7, providing deeper insights into the post-translational regulation of AtACS7 in Arabidopsis.

TSPO-induced degradation of the ethylene receptor RhETR3 promotes salt tolerance in rose (Rosa hybrida).

The gaseous plant hormone ethylene regulates plant development, growth, and responses to stress. In particular, ethylene affects tolerance to salinity; however, the underlying mechanisms of ethylene signaling and salt tolerance are not fully understood. Here, we demonstrate that salt stress induces the degradation of the ethylene receptor ETHYLENE RESPONSE 3 (RhETR3) in rose (Rosa hybrid). Furthermore, the TspO/MBR (Tryptophan-rich sensory protein/mitochondrial benzodiazepine receptor) domain-containing membrane protein RhTSPO interacted with RhETR3 to promote its degradation in response to salt stress. Salt tolerance is enhanced in RhETR3-silenced rose plants but decreased in RhTSPO-silenced plants. The improved salt tolerance of RhETR3-silenced rose plants is partly due to the increased expression of ACC SYNTHASE1 (ACS1) and ACS2, which results in an increase in ethylene production, leading to the activation of ETHYLENE RESPONSE FACTOR98 (RhERF98) expression and, ultimately accelerating H2O2 scavenging under salinity conditions. Additionally, overexpression of RhETR3 increased the salt sensitivity of rose plants. Co-overexpression with RhTSPO alleviated this sensitivity. Together, our findings suggest that RhETR3 degradation is a key intersection hub for the ethylene signalling-mediated regulation of salt stress.

The Ethylene Biosynthetic Enzymes, 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase (ACS) and ACC Oxidase (ACO): The Less Explored Players in Abiotic Stress Tolerance.

Ethylene is an essential plant hormone, critical in various physiological processes. These processes include seed germination, leaf senescence, fruit ripening, and the plant's response to environmental stressors. Ethylene biosynthesis is tightly regulated by two key enzymes, namely 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxidase (ACO). Initially, the prevailing hypothesis suggested that ACS is the limiting factor in the ethylene biosynthesis pathway. Nevertheless, accumulating evidence from various studies has demonstrated that ACO, under specific circumstances, acts as the rate-limiting enzyme in ethylene production. Under normal developmental processes, ACS and ACO collaborate to maintain balanced ethylene production, ensuring proper plant growth and physiology. However, under abiotic stress conditions, such as drought, salinity, extreme temperatures, or pathogen attack, the regulation of ethylene biosynthesis becomes critical for plants' survival. This review highlights the structural characteristics and examines the transcriptional, post-transcriptional, and post-translational regulation of ACS and ACO and their role under abiotic stress conditions. Reviews on the role of ethylene signaling in abiotic stress adaptation are available. However, a review delineating the role of ACS and ACO in abiotic stress acclimation is unavailable. Exploring how particular ACS and ACO isoforms contribute to a specific plant's response to various abiotic stresses and understanding how they are regulated can guide the development of focused strategies. These strategies aim to enhance a plant's ability to cope with environmental challenges more effectively.

1-methylcyclopropene combined with ethylene absorbent delays the ripening of ‘Fenjiao’ banana (Musa ABB Pisang Awak)

The 'Fenjiao' banana (Musa ABB Pisang Awak) has a high commercial and nutritional value and is harvested when it is highly plump at between 85 and 90 % commercial maturity. The fruit are less angular at this stage. However, these fruit soften rapidly after harvest. 1-Methylcyclopropene (1-MCP) significantly delays ripening, but it can cause ripening disorders when used improperly. Ethylene absorbent (EA) is also widely used to increase the postharvest life of fruit, but it has less of an effect on 'Fenjiao' banana. This study was conducted to optimize the concentrations of 1-MCP combined with EA to increase the shelf life of these bananas. The results showed that a low concentration of 1-MCP (7 g L−1) combined with EA (2 g kg−1) significantly prolonged the shelf life of the 'Fenjiao' banana and maintained its high quality. The combination of 1-MCP and EA repressed the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, ACC synthase, pectin methylesterase, polygalacturonase and pectate lyase in the peel and pulp of 'Fenjiao' banana, as well as the corresponding levels of expression of MbACS1, MbACO1, MbPG1, MbPL1, except for MbPME1, which are induced by 1-MCP. This study provides a useful technique for preserving 'Fenjiao' fruit with a study on its possible physiological mechanism, which could be applied in the postharvest production of 'Fenjiao' banana.

Constitutive expression of apple endo-POLYGALACTURONASE1 in fruit induces early maturation, alters skin structure and accelerates softening.

During fruit ripening, polygalacturonases (PGs) are key contributors to the softening process in many species. Apple is a crisp fruit that normally exhibits only minor changes to cell walls and limited fruit softening. Here, we explore the effects of PG overexpression during fruit development using transgenic apple lines overexpressing the ripening-related endo-POLYGALACTURONASE1 gene. MdPG1-overexpressing (PGox) fruit displayed early maturation/ripening with black seeds, conversion of starch to sugars and ethylene production occurring by 80 days after pollination (DAP). PGox fruit exhibited a striking, white-skinned phenotype that was evident from 60 DAP and most likely resulted from increased air spaces and separation of cells in the hypodermis due to degradation of the middle lamellae. Irregularities in the integrity of the epidermis and cuticle were also observed. By 120 DAP, PGox fruit cracked and showed lenticel-associated russeting. Increased cuticular permeability was associated with microcracks in the cuticle around lenticels and was correlated with reduced cortical firmness at all time points and extensive post-harvest water loss from the fruit, resulting in premature shrivelling. Transcriptomic analysis suggested that early maturation was associated with upregulation of genes involved in stress responses, and overexpression of MdPG1 also altered the expression of genes involved in cell wall metabolism (e.g. β-galactosidase, MD15G1221000) and ethylene biosynthesis (e.g. ACC synthase, MD14G1111500). The results show that upregulation of PG not only has dramatic effects on the structure of the fruit outer cell layers, indirectly affecting water status and turgor, but also has unexpected consequences for fruit development.

Activation of Gossypium hirsutum ACS6 Facilitates Fiber Development by Improving Sucrose Metabolism and Transport.

Cotton fiber yield depends on the density of fiber cell initials that form on the ovule epidermis. Fiber initiation is triggered by MYB-MIXTA-like transcription factors (GhMMLs) and requires a sucrose supply. Ethylene or its precursor ACC (1-aminocyclopropane-1-carboxylic acid) is suggested to affect fiber yield. The Gossypium hirsutum (L.) genome contains 35 ACS genes (GhACS) encoding ACC synthases. Here, we explored the role of a GhACS family member in the regulation of fiber initiation. Expression analyses showed that the GhACS6.3 gene pair was specifically expressed in the ovules during fiber initiation (3 days before anthesis to 5 days post anthesis, -3 to 5 DPA), especially at -3 DPA, whereas other GhACS genes were expressed at very low or undetectable levels. The expression profile of GhACS6.3 during fiber initial development was confirmed by qRT-PCR analysis. Transgenic lines overexpressing GhACS6.3 (GhACS6.3-OE) showed increased ACC accumulation in ovules, which promoted the formation of fiber initials and fiber yield components. This was accompanied by increased transcript levels of GhMML3 and increased transcript levels of genes encoding sucrose transporters and sucrose synthase. These findings imply that GhACS6.3 activation is required for fiber initial development. Our results lay the foundation for further research on increasing cotton fiber production.

The Potential of Essential Oils from Active Packaging to Reduce Ethylene Biosynthesis in Plant Products. Part 2: Fruits (Blueberries and Blackberries).

Plant essential oils (EOs) have an important ability to inhibit ethylene biosynthesis. Nevertheless, the effects of EOs on the key components of ethylene biosynthesis (l-aminocyclopropane-1-carboxylic (ACC) oxidase activity, ACC synthase activity, and ACC content) have not yet been thoroughly studied. Accordingly, this study focused on the effects of emitted EOs from active packaging (EO doses from 100 to 1000 mg m-2) on the key components of ethylene biosynthesis of blueberries and blackberries under several storage temperatures. Anise EO and lemon EO active packaging induced the greatest inhibitory effects (60-76%) on the ethylene production of blueberries and blackberries, respectively, even at high storage temperatures (22 °C). In terms of EO doses, active packaging with 1000 mg m-2 of anise EO or lemon EO led to the highest reduction of ethylene production, respectively. At 22 °C, the investigated EO active packing reduced the activities of ACC synthase and ACC oxidase up to 50%. In order to minimise ethylene biosynthesis in blueberries and blackberries when they are stored even under improper temperature scenarios at high temperatures, this EO active packaging is a natural and efficient technological solution.

The Potential of Essential Oils from Active Packaging to Reduce Ethylene Biosynthesis in Plant Products. Part 1: Vegetables (Broccoli and Tomato).

Essential oils (EOs) extracted from plants have a high potential to reduce ethylene biosynthesis, although their effects have not been deeply studied yet on the key components of the ethylene biosynthesis pathway: l-aminocyclopropane-1-carboxylic (ACC) oxidase activity, ACC synthase activity, and ACC content. Hence, the present study aimed to elucidate the effects of released EOs from active packaging (with different EO doses ranging from 100 to 1000 mg m-2) on the ethylene biosynthesis key components of broccoli and tomato under different storage temperature scenarios. The largest ethylene inhibitory effects on broccoli and tomatoes were demonstrated by grapefruit EO and thyme essential EO (up to 63%), respectively, which were more pronounced at higher temperatures. Regarding EO doses, active packaging with a thyme EO dose of 1000 mg m-2 resulted in the strongest reduction (33-38%) of ethylene production in tomatoes. For broccoli, identical results were shown with a lower grapefruit EO dose of 500 mg m-2. The studied EO-active packaging decreased ACC synthase and ACC oxidase activities by 40-50% at 22 °C. Therefore, this EO-active packaging is a natural and effective technology to reduce ethylene biosynthesis in broccoli and tomatoes when they are stored, even in unsuitable scenarios at high temperatures.

Hydrogen sulfide delays softening of banana fruit by inhibiting cell wall polysaccharides disassembly

SummaryHarvested banana undergoes rapid softening, which limits its shelf life. To delay softening, banana fruit was treated with hydrogen sulfide (H2S) emitted by 0.6 mm sodium hydrosulfide (NaHS) and stored at 15 °C for 16 days. The effects of H2S on cell wall degradation and other physiological characteristics were investigated. In comparison to control fruits, H2S‐treated bananas retained a higher level of fruit firmness, but lower hue values. Ethylene metabolism analysis suggested that H2S inhibited the production of ethylene and the accumulation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and decreased the activities of ACC synthase (ACS) and ACC oxidase (ACO). Cell wall polysaccharides determination assays suggested that H2S treatment increased the proportion of HCl‐soluble pectin (HSP), NaOH‐soluble pectin (NSP), cellulose and hemicellulose but decreased water‐soluble pectin (WSP) in fruits. H2S treatment also inhibited the activities of polysaccharide degrading enzymes such as polygalacturonase (PG), pectin methylesterase (PME), pectin lyase (PL), cellulase (CL) and β‐galactosidase (β‐Gal). Transmission electron microscopy analysis suggested that H2S protected cell walls from structural breakdown. These results indicated that H2S is effective in delaying banana softening by regulating cell wall polysaccharide metabolism.

PbrWRKY70 increases pear (Pyrus bretschneideri Rehd) black spot disease tolerance by negatively regulating ethylene synthesis via PbrERF1B-2

Various pear plant cultivars exhibit diverse abilities to resist pear black spot disease (BSD), while the precise molecular mechanisms of resistance against pear BSD remain unclear. This study proposed a profound expression of a WRKY gene, namely PbrWRKY70, derived from Pyrus bretschneideri Rehd, within a BSD-resistant pear cultivar. Comparative analysis against the wild-type revealed that the overexpression of PbrWRKY70 engendered augmented BSD resistance of transgenic Arabidopsis thaliana and pear calli. Notably, the transgenic plants exhibited higher activities of superoxide dismutase and peroxidase, along with an elevated capacity to counteract superoxide anions via increased anti-O2-. Additionally, these plants displayed diminished lesion diameter, as well as reduced levels of hydrogen peroxide, malondialdehyde and 1-aminocyclopropane-1-carboxylic acid (ACC) contents. We subsequently demonstrated that PbrWRKY70 selectively bound to the promoter region of ethylene-responsive transcription factor 1B-2 (PbrERF1B-2), a potential negative regulator of ACC, thereby downregulating the expression of ACC synthase gene (PbrACS3). Consequently, we confirmed that PbrWRKY70 could enhance pear resistance against BSD by reducing ethylene production via modulation of the PbrERF1B-2-PbrACS3 pathway. This study established the pivotal relationship among PbrWRKY70, ethylene synthesis and pear BSD resistance, fostering the development of novel BSD-resistant cultivars. Furthermore, this breakthrough holds the potential to enhance pear fruit yield and optimize storage and processing during the later stages of fruit maturation.

Melatonin influences methyl jasmonate-induced protection of photosynthetic activity in wheat plants against heat stress by regulating ethylene-synthesis genes and antioxidant metabolism

Melatonin (MT) and methyl jasmonate (MeJA) play important roles in the adaptation of plants to different stress factors by modulating stress tolerance mechanisms. The present study reports the involvement of MT (100 µM) in MeJA (10 µM)-induced photosynthetic performance and heat stress acclimation through regulation of the antioxidant metabolism and ethylene production in wheat (Triticum aestivum L.) plants. Plants exposed to 40 °C for 6 h per day for 15 days and allowed to retrieve at 28 °C showed enhanced oxidative stress and antioxidant metabolism, increased 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) activity and ethylene production, and decreased photosynthetic performance. In contrast, the exogenously applied MT and MeJA reduced oxidative stress through improved S-assimilation (+ 73.6% S content), antioxidant defense system (+ 70.9% SOD, + 115.8% APX and + 104.2% GR, and + 49.5% GSH), optimized ethylene level to 58.4% resulting in improved photosynthesis by 75%. The use of p-chlorophenyl alanine, a MT biosynthesis inhibitor along with MeJA in the presence of heat stress reduced the photosynthetic performance, ATP-S activity and GSH content, substantiated the requirement of MT in the MeJA-induced photosynthetic response of plants under heat stress. These findings suggest that MeJA evoked the plant’s ability to withstand heat stress by regulating the S-assimilation, antioxidant defense system, and ethylene production, and improving photosynthetic performance was dependent on MT.

NaWRKY3 is a master transcriptional regulator of the defense network against brown spot disease in wild tobacco.

WRKY transcription factors are involved in plant defense against pathogens. No WRKYs have been reported to be involved in resistance to tobacco brown spot disease caused by Alternaria alternata. Here, we found that NaWRKY3 plays a critical role in Nicotiana attenuata defense against A. alternata. NaWRKY3 bound and regulated many defense genes, including: lipoxygenase 3, ACC synthase 1, and ACC oxidase 1, three jasmonate- and ethylene-biosynthetic genes; feruloyl-CoA 6'-hydroxylase 1 (NaF6'H1), the biosynthetic gene for the phytoalexins scopoletin and scopolin; and three A. alternata resistance genes, the long non-coding RNA L2, NADPH oxidase (NaRboh D), and berberine bridge-like (NaBBL28). Silencing L2 reduced jasmonate concentrations and NaF6'H1 expression. NaRboh D-silenced plants were severely impaired in reactive oxygen species production and stomatal closure responses. NaBBL28 was the first A. alternata resistance BBL identified and was involved in the hydroxylation of 17-hydroxygeranyllinalool diterpene glycosides. NaWRKY3 bound to its own promoter but repressed its expression. Thus, we demonstrated that NaWRKY3 is a fine-tuned master regulator of the defense network against A. alternata in N. attenuata by regulating several signaling pathways and defense metabolites. This is the first time such an important WRKY has been identified in Nicotiana species, providing new insights into defense against A. alternata.

Ethanol fermentation- and ethylene physiology-related gene expression profiles in Red Delicious apples stored under variable hypoxic conditions and protocols

Dynamic Controlled Atmosphere (DCA) is beneficial in maintaining specific quality parameters but, due to the extreme oxygen levels applied, can cause adverse effects on the fruit by inducing excessive anaerobic metabolism and the production of off-flavors. The metabolic adaptation and responses of apples (Malus domestica Borkh.) cv. Red Delicious to static or dynamic oxygen concentrations (0.3 and 0.8%, with sequential shifts) during cold storage for 7 months were studied by monitoring quality parameters and the expression of genes involved in sugar, fermentative metabolism, and ethylene physiology. Ethanol content reached the highest levels (around 400 mg/kg FW) under 0.3% oxygen concentration and fruit firmness appeared to be reduced in samples accumulating the highest levels of ethanol. Oxygen switch was effective in reducing the ethanol concentrations with timing-dependent variable effects. The expression of fermentative (alcohol dehydrogenase, lactate dehydrogenase, pyruvate decarboxylase) and sugar metabolism (β-amylase; phosphofructokinase; sucrose synthase) genes resulted to be differently affected by the hypoxic conditions imposed, in particular during the early stages of storage. Sucrose synthase expression appeared to be highly sensitive to changes in low oxygen concentration. Ethylene biosynthesis (ACC synthase and oxidase) genes showed marked differences in their expression in relation to the static and dynamic protocols and the hypoxic conditions, as well as six Ethylene Responsive Factors (ERF) genes, some of them possibly involved in the oxygen sensing mechanism operating in fruit tissues.

Citrus ACC synthase CiACS4 regulates plant height by inhibiting gibberellin biosynthesis.

Dwarfism is an agronomic trait that has substantial effects on crop yield, lodging resistance, planting density, and a high harvest index. Ethylene plays an important role in plant growth and development, including the determination of plant height. However, the mechanism by which ethylene regulates plant height, especially in woody plants, remains unclear. In this study, a 1-aminocyclopropane-1-carboxylic acid synthase (ACC) gene (ACS), which is involved in ethylene biosynthesis, was isolated from lemon (Citrus limon L. Burm) and named CiACS4. Overexpression of CiACS4 resulted in a dwarf phenotype in Nicotiana tabacum and lemon and increased ethylene release and decreased gibberellin (GA) content in transgenic plants. Inhibition of CiACS4 expression in transgenic citrus significantly increased plant height compared with the controls. Yeast two-hybrid assays revealed that CiACS4 interacted with an ethylene response factor (ERF), CiERF3. Further experiments revealed that the CiACS4-CiERF3 complex can bind to the promoters of 2 citrus GA20-oxidase genes, CiGA20ox1 and CiGA20ox2, and suppress their expression. In addition, another ERF transcription factor, CiERF023, identified using yeast one-hybrid assays, promoted CiACS4 expression by binding to its promoter. Overexpression of CiERF023 in N. tabacum caused a dwarfing phenotype. CiACS4, CiERF3, and CiERF023 expression was inhibited and induced by GA3 and ACC treatments, respectively. These results suggest that the CiACS4-CiERF3 complex may be involved in the regulation of plant height by regulating CiGA20ox1 and CiGA20ox2 expression levels in citrus.

Application of Anantmul (Hemidesmus indicus) root extract improves postharvest shelf-life of dessert banana

Banana (Musa sp.), a climacteric fruit ripens rapidly after harvesting resulting in a very short postharvest shelf-life. Exogenous salicylic acid (SA) treatment is one of the widely adopted practices to improve postharvest shelf-life of banana. The rationale behind such chemical treatment is to slow down climacteric ripening that involves ethylene production along with boosting of defence responses against fruit pathogens. In this study, we assessed the possibility of replacing chemically synthesized SA with a plant-based natural product (PBNP), 2-hydroxy-4-methoxy benzaldehyde (MBALD), a substituted analogue to SA, sourced from roots of Hemidesmus indicus. Dessert banana fingers (cv. Kanthali and cv. Malbhog) harvested after 80 days of post-anthesis were subjected to postharvest treatment by dipping in treatment solution for 8 h. Four different experimental sets namely, water (C), 2 mM MBALD (T1), 1 mM SA (T2) and 200 g/L H. indicus root extract (T3) were employed. After treatment, the fingers were stored at 25 ± 2 °C with 90 ± 2% relative humidity (RH) for 10 days but examined at an interval of 24 h. Ripening-related physicochemical and physiological changes decreased in T1, T2 and T3 in comparison with control (C). Reduced in vitro activities of major cell wall degrading enzymes were observed in all the treatments (T1, T2, T3) when compared with control (C). Expression of candidate genes of ethylene biosynthesis namely, ACC synthase (ACS), ACC oxidase (ACO), along with chitinase (CHT) and pathogen-related protein-1 (PR1) were found to be suppressed in all the treatments with T3 to be the best performer. Furthermore, in vitro culture of latently infected fruit mycoflora when grown in the presence of T3 showed a substantial reduction in growth rate. Such observation makes T3 a promising alternative to choose in the postharvest management of banana.