Accumulation Of Organic Acids Research Articles

Identification of co-expressed networks and key genes associated with organic acid in peach fruit

• The number of DEGs increased along with fruit development taking stage 1 as control. • Transcription factors play crucial role during organic acid accumulation in fruit. • Hydrogen ion transportation contributes to organic acid accumulation. Malate, citrate, and quinate are the major organic acids in ripen peach fruit, the content of which undergoes considerable variations during fruit development and maturation. The molecular mechanisms underlying these variations remain largely unclear. In this study, weighted gene co-expression network analysis (WGCNA) of two accessions in five developmental stages was performed to identify networks and key genes associated with main organic acids. The obtained hubgenes were screened by comparative transcriptome analysis of 102 peach accessions. Combined with functional annotation, three genes encoding WRKY50, MYB62, and cation/H+ exchanger 18, respectively, were detected as candidate genes related with malate content. One gene encoding bHLH1 was considered as candidate genes associated with citrate content. The four candidate genes were validated by integrated analysis of phenotype and expression analysis of ‘Jintong 5’, a randomly selected accession. These findings provide new sight to our existing knowledge of organic acid regulation in peach.

METABOLIC ACTIVITY OF LACTIC ACID BACTERIAL STRAINS AFTER THEIR INTRODUCTION INTO ALFALFA HAYLAGE

Objective. Study the metabolic activity of strains of lactic acid bacterial strains after their introduction into alfalfa haylage as a component of preservatives. Methods. Microbiological (determining the number of microorganisms, obtaining antibiotic-resistant mutants of bacterial strains), zootechnical (pH level, accumulation and ratio of organic acids in the fermentation process), statistical. Results. Lactobacillus plantarum KT-L18/1str, L. plantarum 32str strains introduced into the haylage substrate are stored in the feed in an active state for a long time and at day 30 of fermentation take a dominant position among native lactic acid bacteria, retaining 80 % of the acid-forming capacity and antagonistic activity against Staphylococcus aureus. The best results of the action of the studied lactic acid bacteria (LAB) after introduction into alfalfa haylage were obtained when the mass was dry-cured to a moisture content of 60–61 %, while the share of lactic acid in the total amount of organic acids formed in the experimental variants of the haylage ranged from 85.5 % to 89.3 % versus the control, where the share of lactic acid reached only 42 %. Increasing the degree of feed acidification in experimental variants at a given alfalfa moisture content ensured a decrease in the butyric acid content to 1.12–1.7 % versus 26.3 % in the control variant. Treatment of alfalfa haylage dry-cured to a moisture content of 38–39 % with strains of lactic acid bacteria did not affect the increase in the proportion of lactic acid. Conclusion. The use of probiotic L. plantarum KT-L18/1str and L. plantarum 32str made it possible to establish their competitiveness and metabolic activity in the process of alfalfa haylage preparation. The use of LAB probiotic strains for alfalfa haylage preparation improved fermentation processes, in particular, when dry matter content was at the level of 39–40 %.

Exogenous γ-aminobutyric acid strengthens phenylpropanoid and nitrogen metabolism to enhance the contents of flavonoids, amino acids, and the derivatives in edamame.

γ-aminobutyric acid (GABA) has been reported to improve stress resistance in plants. Nonetheless, little is known about the effects of GABA on the nutritional quality and regulatory mechanisms of edamame. Therefore, we analyzed the flavonoid and amino acid (AA) metabolism and the effects of GABA on the nutrient content of edamame seeds through physiological and metabolomic analyses. Exogenous GABA increased endogenous GABA metabolism and GABA transaminase activity and enhanced the oxoglutarate content, which entered into nitrogen metabolism and increased the activity and expression of nitrogen metabolism-related enzymes, to accumulate AAs and bioactive peptides. Meanwhile, exogenous GABA induced the metabolism of flavonoids, including total flavonoids, anthocyanins, 6''-o-malonyglycitin, glycitin, ononin, cyanin, and ginkgetin, by increasing the activity and expression of flavonoid biosynthetic enzymes. This is the first study to reveal that GABA effectively improves the nutritional quality of edamame through the accumulation of AAs, bioactive peptides, isoflavones, anthocyanins, sugars, and organic acids.

Combined transcriptome and metabolome analysis revealed pathways involved in improved salt tolerance of Gossypium hirsutum L. seedlings in response to exogenous melatonin application

BackgroundSalinization is major abiotic stress limiting cotton production. Melatonin (MT) has been implicated in salt stress tolerance in multiple crops including upland cotton. Here, we explored the transcriptomic and metabolomic response of a salt-tolerant self-bred high-yielding cotton line SDS-01, which was exogenously sprayed with four MT concentrations (50, 100, 200, and 500 μM).ResultsHere we found that MT improves plant biomass and growth under salt stress. The combined transcriptome sequencing and metabolome profiling approach revealed that photosynthetic efficiency is improved by increasing the expressions of chlorophyll metabolism and antenna proteins in MT-treated seedlings. Additionally, linoleic acid and flavonoid biosynthesis were improved after MT treatment. The Na+/K+ homeostasis-related genes were increasingly expressed in salt-stressed seedlings treated with MT as compared to the ones experiencing only salt stress. Melatonin treatment activated a cascade of plant-hormone signal transduction and reactive oxygen scavenging genes to alleviate the detrimental effects of salt stress. The global metabolome profile revealed an increased accumulation of flavonoids, organic acids, amino acids and derivatives, saccharides, and phenolic acids in MT-treated seedlings. Interestingly, N, N′-Diferuloylputrescine a known antioxidative compound was highly accumulated after MT treatment.ConclusionCollectively, our study concludes that MT is a salt stress regulator in upland cotton and alleviates salt-stress effects by modulating the expressions of photosynthesis (and related pathways), flavonoid, ROS scavenging, hormone signaling, linoleic acid metabolism, and ion homeostasis-related genes.

Fulvic acid mitigates cadmium toxicity-induced damage in cucumber seedlings through the coordinated interaction of antioxidant enzymes, organic acid, and amino acid.

Fulvic acid (FA) can significantly alleviate cadmium (Cd) stress, but the specific metabolic response of FA to Cd toxicity is still not clarified. In the present study, we used untargeted metabolomic [gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS)] analysis to profile cucumber metabolism in response to Cd stress after spray application of FA. Our results showed that 331 differentially enriched metabolites (DEMs) were identified in leaf materials. These DEMs were enriched in 21 shared pathways in comparative groups of "Cd treatment vs. the control treatment" and "FA + Cd treatment vs. the Cd treatment." Specifically, treatment with FA significantly enhanced the organic acid content (citric acid, isocitric acid, 2-oxoglutaric acid, fumaric acid, and malic acid), which would contribute to provide sufficient substrates for the tricarboxylic acid (TCA) cycle and amino acid biosynthesis, thereby ensuring the normal production of energy and amino acid. At the same time, FA significantly increased the amino acid content (aspartate, citrulline, histidine, leucine, and phenylalanine). The accumulation of organic acid and amino acid can act as chelating agents for heavy metal ions and as scavengers of reactive oxygen species (ROS), thereby reducing intracellular oxidative damage. Furthermore, the application of FA improves antioxidant enzymes and accelerates ROS clearance. The improved contents of organic acid and amino acid, and the increased activity of antioxidant enzymes both played a central role in the reduction of malondialdehyde (MDA, 14.08%), hydrogen peroxide (H2O2, 61.70%) contents, and superoxide anion radical (O2-, 30.41%) production rate in plants under Cd stress. Taken together, the present study demonstrates the effects of FA on the antioxidant capacity and carbohydrate and amino acid metabolism of cucumber seedlings exposed to Cd stress, which provides comprehensive insights into the regulation of plants' response to Cd toxicity with FA was applied in cucumber.

The Effect of Short-Term Temperature Pretreatments on Sugars, Organic Acids, and Amino Acids Metabolism in Valencia Orange Fruit

Temperature pretreatment is one of the most important factors which significantly affects the postharvest quality of citrus fruit. In this study, late-ripening Valencia orange (citrus sinensis) fruits were used to investigate the effect of short-term treatment at low (6°C), room (20°C), and high (40°C) temperatures on fruit quality. Our results revealed that both low and room-temperature treatments maintained the content of sugars and organic acids, whereas high-temperature treatments elevated the accumulation of sugars but decreased the content of citric acid. In fruit peel (flavedo and albedo), the accumulation of sugars and organic acids responding to temperatures was diverse and mostly different from that in the pulp. Meanwhile, GABA and several amino acids were upregulated under short-term high-temperature treatment but downregulated in response to low-temperature treatment in both peel and pulp. Furthermore, PCA and correlation analysis revealed that the short-term temperature treatments changed the metabolic flow, and GABA was positively correlated with sugars and organic acids. Our study analyzed the metabolic changes of fruit peel and pulp in response to short-term temperature treatments and revealed that GABA may act as a signaling molecular involved in temperature-controlled quality changes.

Physiological and molecular adaptations of Citrus grandis roots to long-term copper excess revealed by physiology, metabolome and transcriptome

Little information is available on the physiological and molecular adaptations of plant roots to long-term copper (Cu) excess revealed by combined analysis of physiology, widely targeted metabolome and RNA-Seq. ‘Shatian’ pummelo [ Citrus grandis (L.) Osbeck] seedlings were supplied six times weekly with nutrient solution at a Cu concentration of 400 (excessive Cu) or 0.5 (control) μM for six months. Thereafter, excessive Cu impacts on gene expression, metabolites, cell wall (CW) materials and components, as well as some other physiological parameters in roots were examined. We detected 350 upregulated and 156 downregulated genes, and 142 [90 secondary metabolites (SMs) and 52 primary metabolites (PMs)] upregulated and 48 (31 SMs and 17 PMs) downregulated metabolites in 400 μM Cu-treated roots (RCu400). Our results suggested that the physiological and molecular adaptions of roots to Cu excess included: (a) increased biosynthesis and accumulation of SMs (lignin, alkaloids, flavonoids, lignans and coumarins, phenolic acids and total phenolics); (b) elevated Cu retention in root CW and reduced Cu transfer to shoots due to increased thickness and lignification of root CW; (c) downregulated and upregulated expression of Cu uptake- and homeostasis-related genes, respectively; and (d) improved capacity to maintain iron homeostasis in cytoplasm and energy homeostasis due to increased accumulation of carbohydrates and organic acids and production of ATP. Although the abundances of many metabolites and the expression levels of some genes related to the detoxification of reactive oxygen and nitrogen species were elevated in RCu400, they could not protect these roots from oxidative damage. Also, we observed some similarities and differences in excessive Cu-responsive genes and metabolites between leaves and roots. • Cu excess caused extensive reprogramming of genes and metabolites in Citrus roots. • Excessive Cu-responsive genes and metabolites differed between leaves and roots. • Cu-stress elevated SM biosynthesis and level in roots, thus enhancing Cu-tolerance. • Cu-stress increased Cu retention in RCW and decreased Cu transfer to shoots. • Cu uptake (homeostasis)-related genes were inhibited (induced) in Cu-stress roots.

Effects of rainproof cultivation on organic acid accumulation related gene expression of Ziziphus jujuba ‘Dongzao’

Effects of rainproof cultivation on organic acid accumulation related gene expression of <i>Ziziphus jujuba</i> ‘Dongzao’

Effect of corn stover hydrochar on anaerobic digestion performance of its associated wastewater

Hydrothermal carbonation (HTC) is an effective method to enhance the fuel quality of biomass in a subcritical water environment, but generates large amounts of wastewater (HTCWW), which was converted through anaerobic digestion (AD) into methane in this study. However, the toxic and refractory substances contained in HTCWW tended to cause operation instability of the AD system. The solid product in HTC of corn stover (CS), named CS hydrochar, was modified with KOH immersion and then added to the AD reactor to improve the methanogenic performance. The results showed that the optimum dosage of modified hydrochar (MCH) was 15 g/L, and the COD removal rate was increased by 19.3% and methane yield was increased by 42.3%–301 mL/g-COD, as the pore and the oxygen-containing functional groups of MCH provided colonization points for microorganisms, and also enhanced the electron transfer efficiency among methanogenic archaea. In addition, the increased alkalinity of MCH due to alkaline modification increased the pH buffering capability, and accelerated the consumption of acetic acid and butyric acid in the early AD stage (0–8 days) and propionic acid in the late AD stage (12–18 days), which then alleviated the organic acid accumulation and reduced the lag period by 2 days. The adverse effects of toxic and refractory substances of HTCWW on the AD performance were also decreased due to the adsorption of MCH at the beginning of the AD process, and latterly the adsorbed substances could be degraded by the microorganisms colonized on the MCH surface. The finding of this study showed AD is a feasible method to recover organic energy contained in HTCWW, and the associated hydrochar can be used as an effective promoter for the AD of HTCWW.

WGCNA analysis revealing molecular mechanism that bio-organic fertilizer improves pear fruit quality by increasing sucrose accumulation and reducing citric acid metabolism.

It’s been long known that the application of organic fertilizer (OF) and bio-organic fertilizer (BF) which containing beneficial microorganisms to pear trees can both significantly improve fruit quality and yield. In order to reveal the mechanism of BF and OF regulating fruit growth and quality in pear, the effects of BF and OF on the photosynthetic characteristics and the accumulation of major sugars and organic acids of the pear fruit were quantified compared with chemical fertilizer (CF). Additionally, the molecular mechanisms regulating pear fruit development and quality were studied through transcriptome analysis. The three treatments were conducted based on the same amounts of nitrogen supply. The results showed that compared with CF, BF and OF treatments increased the fruit yield, and also significantly improved the photosynthesis efficiency in pear. BF and OF both significantly increased the sucrose content but significantly decreased the fructose and glucose content within the pear fruit. The amount of malic acid was significantly higher in OF treatment. Compared with CF and OF, BF significantly increased the sugar-acid ratio and thus improved the fruit quality. Transcriptome analysis and weighted correlation network analysis (WGCNA) revealed that the sugar metabolism of fruits applied with the BF was enhanced compared with those applied with CF or OF. More specifically, the expression of SDH (Sorbitol dehydrogenase) was higher in BF, which converts sorbitol into fructose. For both of the OF and BF, the transcript abundance of sugar transporter genes was significantly increased, such as SOT (Sorbitol transporter), SUT14 (Sugar transport 14), UDP-GLUT4 (UDP-glucose transporter 4), UDP-SUT (UDP-sugar transporter), SUC4 (Sucrose transport 4), SUT7 (Sugar transporter 7), SWEET10 and SWEET15 (Bidirectional sugar transporter), which ensures sugar transportation. The genes involved in organic acid metabolism showed decreased transcripts abundance in both BF and OF treatments, such as VAP (Vesicle-associated protein) and cyACO (Cytosolic aconitase), which reduce the conversion from succinate to citric acid, and decrease the conversion from citric acid to malic acid in the TCA cycle (Tricarboxylic Acid cycle) through Pept6 (Oligopeptide transporter). In conclusion, the application of BF and OF improved fruit quality by regulating the expression of sugar and organic acid metabolism-related genes and thus altering the sugar acid metabolism. Both BF and OF promote sucrose accumulation and citric acid degradation in fruits, which may be an important reason for improving pear fruit quality. The possible mechanism of bio-organic fertilizer to improve fruit quality was discussed.

Suaeda glauca and Suaeda salsa Employ Different Adaptive Strategies to Cope with Saline–Alkali Environments

(1) Background: soil salinization has become a global problem that restricts agricultural production; thus, there is a need to explore the special survival strategies of halophytes in saline–alkali environments. (2) Methods: this study conducted a comparative analysis of the differences in metabolites and mineral elements between two indicator plants (Suaeda glauca and Suaeda salsa) in the study area. (3) Results: S. salsa leaves accumulated more total nitrogen (TN), total organic carbon (TOC), calcium (Ca), sodium (Na) and manganese (Mn). The Na/K analysis showed that S. salsa was more tolerant of saline–alkali environments than S. glauca. Metabolite analysis revealed a significant increase in added sugars in S. salsa compared with S. glauca and a significant accumulation of most organic acids associated with the TCA cycle, which suggests an enhancement in the flow of carbon from glycolysis to the TCA cycle. In addition, the content of phenolic substances, such as phenylpropane compounds and flavonols, also changed in saline–alkali environments, which may have promoted the metabolism of organic acids. (4) Conclusions: during the process of plant adaptation to salinity, the central metabolism of S. glauca was nitrogen metabolism, while that of S. salsa was organic acid metabolism.

Comparative effects of different potassium sources on soluble sugars and organic acids in tomato

Soluble sugars and organic acids are mainly decisive factor of flavor quality in tomato. Potassium (K), an essential macroelement, plays key roles in regulation of plant growth, stress responses and fruit quality. However, the comparative effects of different K fertilizer on soluble sugars and organic acids accumulation and the differential mechanisms are still unknown. The aim of this study was to investigate how K fertizliers (K_Cl, K_S) affect the accumulations of soluble sugars and organic acids in tomato fruits. The results indicated that K applications improved fruit flavor quality of tomato, as supported by the increased concentrations of soluble solid, titratable acid, fructose, glucose, sucrose (Suc), citric acid (CA) and malic acid (MA). Further study showed that K application increased the accumulations of soluble sugars by improving Suc metabolism, sink strength and Suc transport due to the increased expressions of Suc-metabolizing enzyme genes and SlSWEETs and SlSUTs in tomato. K applications increased the accumulations of MA and CA by improving CA synthesis and TCA cycle due to the increased expressions CA-metabolizing enzyme genes. Moreover, more Suc of leaves were transferred into fruits in K4_Cl treatment, which was supported by the lower concentrations of soluble sugars and higher expressions of SlSUT1 and SlSWEET11b in leaves. More carbohydrates were allocated to form yield and metabolic substrate in K4_S treatment, which was supported by the higher expressions of SlSUT4 and more differential metabolic pathway in fruits. Finally, the carbohydrates transports and allocations were involved in the differential mechanisms of soluble sugar accumulations in response to K_S and K_Cl in tomato.

Ionomic and metabolic responses of wheat seedlings to PEG-6000-simulated drought stress under two phosphorus levels.

BackgroundWheat (Triticum aestivum L.) is a major food crop worldwide. Low soil phosphorus content and drought are the main constraints on wheat production in Xinjiang, China.MethodsIn this study, the ionic and metabolic responses of one wheat variety (“Xindong20”) to drought stress simulated by using polyethylene glycol 6000 (PEG-6000) were investigated under low phosphorus (LP) and conventional phosphorus (CP) conditions by analysing wheat mineral elements and metabolites. Besides, due to xanthohumol was the metabolite with the most significant difference in expression detected in “Xindong 20”, two wheat variety “Xindong20 and Xindong 23” were selected to conduct the germination test simultaneously, to further verify the function of xanthohumol in wheat growth. Xanthohumol was mixed with PEG solution (20%) to prepare PEG solutions with different concentrations (0%, 0.1%, 0.5%, and 1%) of xanthohumol. Then wheat grains were soaked in the solutions for 20 hours, followed by a germination test. After 7 days, the indicators including shoot length, max root length, and root number were determined to identify whether the metabolite was beneficial to improve the drought tolerance of wheat.ResultsThe results showed that the root density and volume of wheat in LP treatment were higher than those in CP treatment. The roots underwent programmed cell death both in LP and CP treatments under PEG-6000-simulated drought stress, however, the DNA degradation in root cells in LP treatment was lower than that in CP treatment after rehydration for 3 d. Before drought stress, the malondialdehyde (MDA) content in shoot and the peroxidase (POD) activity in root in LP treatment were significantly higher than those in CP treatment, while the soluble sugar content and chlorophyll content in LP treatment were significantly lower than those in CP treatment. During drought stress, the POD activity maintained at a high level and the soluble sugar content gradually increased in LP treatment. After rehydration, the MDA content still maintained at a high level in LP treatment, the superoxide dismutase (SOD) activity increased, and the contents of soluble sugar and chlorophyll were significantly higher than those in CP treatment. The analysis of mineral elements and metabolites showed that the wheat in CP treatment was more sensitive to drought stress than that in LP treatment. Besides, the effect of drought stress was greater on shoot than on root in CP treatment, while it was opposite in LP treatment. The effect of drought stress on sugar metabolism gradually increased. Germination assays showed that 0.1% exogenous xanthohumol addition could significantly increase the shoot length of the two wheat varieties under drought stress.ConclusionAppropriate low phosphorus supply could increase antioxidant enzyme activity in wheat, and enhance sugar metabolism to regulate osmotic balance, as well as the accumulation of various organic acids to maintain the intracellular ion homeostasis. Therefore, compared to the conventional phosphorus supply level, appropriate low phosphorus supply can significantly improve the drought tolerance of wheat. Additionally, addition of 0.1% exogenous xanthohumol, an important differential expressed metabolite in drought-stressed wheat, could effectively promote wheat shoot growth under drought stress.

Simulated Microgravity Accelerates Alloy Corrosion by Aspergillus sp. via the Enhanced Production of Organic Acids.

Metal corrosion caused by Aspergillus sp. was shown to be significantly enhanced on a space station, but its mechanism is still unknown. To simulate this on earth, the corrosion capability of A. carbonarius on five metal sheets was investigated under simulated microgravity. Also, the effect of metal ions on growth and organic acid production was determined. Results showed that A. carbonarius could corrode all five types of metal, including Ti alloy, aluminum alloy, iron, and aluminum and copper sheet, and the corrosion was intensified under simulated microgravity. Energy dispersive X-ray spectrometry (EDS) analysis showed that metal ions enriched on A. carbonarius spores, especially iron, aluminum ions, and copper ions, indicating that A. carbonarius can use these metal ions. In particular, the content of oxalic acid was significantly increased after A. carbonarius cocultured with five metal materials under simulated microgravity. Al3+, Fe3+, and Cu2+ at the concentration of 0.3 mg/mL and Mg2+ at 0.8 mg/mL significantly promoted the growth and oxalic acid and citric acid production of A. carbonarius and A. niger under normal gravity and simulated microgravity. Comparing the impact of metal ions and metal sheets on the production of organic acids, it can be inferred that oxalic acid may dominate in the corrosion process of A. carbonarius. In summary, molds promoted metal corrosion by producing organic acids, and the released metal ions will further promote the growth of mold and the accumulation of organic acids. This may be an important reason for the intensification of mold corrosion under microgravity. IMPORTANCE The space station and other long-term manned spacecrafts will experience the risk of microbial corrosion, especially mold, which will be harmful to the platform system and astronauts. Aspergillus sp. has been widely reported to produce organic acids that corrode and destroy materials, and the ability of these crafts to fly through space can be significantly affected. Research on the mechanism that causes enhanced corrosion ability of fungi in space stations is important to control their growth. Our research focuses on the interaction between mold and metals. In particular, it is found that metal ions promote mold growth and produce organic acids, thus accelerating mold corrosion of metals. Our results provide a new perspective for the control of fungal corrosion under simulated microgravity.

Metabolomic and transcriptomic analyses reveal the mechanism of sweet-acidic taste formation during pineapple fruit development.

Pineapple (Ananas comosus L.) is one of the most valuable subtropical fruit crop in the world. The sweet-acidic taste of the pineapple fruits is a major contributor to the characteristic of fruit quality, but its formation mechanism remains elusive. Here, targeted metabolomic and transcriptomic analyses were performed during the fruit developmental stages in two pineapple cultivars (“Comte de Paris” and “MD-2”) to gain a global view of the metabolism and transport pathways involved in sugar and organic acid accumulation. Assessment of the levels of different sugar and acid components during fruit development revealed that the predominant sugar and organic acid in mature fruits of both cultivars was sucrose and citric acid, respectively. Weighted gene coexpression network analysis of metabolic phenotypes and gene expression profiling enabled the identification of 21 genes associated with sucrose accumulation and 19 genes associated with citric acid accumulation. The coordinated interaction of the 21 genes correlated with sucrose irreversible hydrolysis, resynthesis, and transport could be responsible for sucrose accumulation in pineapple fruit. In addition, citric acid accumulation might be controlled by the coordinated interaction of the pyruvate-to-acetyl-CoA-to-citrate pathway, gamma-aminobutyric acid pathway, and tonoplast proton pumps in pineapple. These results provide deep insights into the metabolic regulation of sweetness and acidity in pineapple.

Organic acid metabolism in Chinese dwarf cherry [Cerasus humilis (Bge.) Sok.] is controlled by a complex gene regulatory network.

The acidity of Chinese dwarf cherry [Cerasus humilis (Bge.) Sok.] fruits is a key factor affecting the sensory quality of fruits, and it undergoes great changes during development. The molecular mechanisms of these changes are still unclear. In this study, fruits of high-acid ‘Nongda4’ and low-acid ‘DS-1’ varieties of Chinese dwarf cherry were used to determine the acid content at different developmental stages. We used transcriptome profiles to identify key genes related to organic acid metabolism and construct their co-expression networks, and we studied the expression patterns of key genes in 36 Chinese dwarf cherry accessions. The titratable acid content of both ‘DS-1’ and ‘Nongda4’ fruits first increased and then decreased during fruit development; however, the titratable acid content of ‘DS-1’ fruits changed to a minor extent. The organic acid content of ‘Nongda4’ was significantly higher than that of ‘DS-1’. The organic acids in mature fruits were mainly malic acid and citric acid. Analysis of the differentially expressed genes related to organic acid metabolism revealed six key genes, including two MDH genes, one tDT gene, one ME gene, one PEPCK gene, and one VHA gene. Weighted gene co-expression network association analysis revealed four modules that were significantly correlated with organic acid content, and 10 key genes with high connectivity among these four modules were screened, including two PK genes, two MDH genes, two ME genes, one PEPCK gene, one VHA gene, one PEPC gene, and one tDT gene. According to the expression patterns of genes in different Chinese dwarf cherry accessions, seven genes were confirmed to represent key genes related to the regulation of organic acids during Chinese dwarf cherry fruit development. These results provide a foundation for further studies on the molecular mechanism of organic acid accumulation in Chinese dwarf cherry fruit.

Transcriptomic analysis reveals key genes regulating organic acid synthesis and accumulation in the pulp of Litchi chinensis Sonn. cv. Feizixiao

• Determining the kinds of the organic acids in the pulp of Feizixiao litchi and observing the dynamic change characteristics of the different organic acids content. • Identifing the key biochemical pathways for the metabolism of the organic acids in the pulp of Feizixiao litchi through RNA-seq. • Confirming the key genes regulating the organic acids accumulation in the pulp of Feizixiao litchi and their expressions characteristics through RNA-seq. • Verifing the expression of the above key genes through real-time fluorescence quantitative PCR. To investigate the gene expression characteristics and patterns of organic acid synthesis and accumulation in the pulp of Litchi chinensis Sonn. cv. Feizixiao (FZX), 16-year-old Feizixiao litchi trees were used as the experimental material, and the dynamic changes in the main organic acids in the pulp were determined for two years. RNA sequencing was carried out when the total acids in the pulp changed drastically 35, 50 and 73 d after anthesis in 2020 to discover the molecular mechanism of the synthesis and accumulation of different organic acids in pulp. The results indicate that tartaric acid and malic acid were the main organic acids in pulp. The RNA-seq contained 165,886 transcripts, and 12 176, 19 835 and 5 048 DEGs were observed in the 35 d vs. 50 d, 35 d vs. 73 d and 50 d vs. 73 d groups, respectively. These expressed transcripts of organic acid metabolism were significantly enriched in correlated pathways, including glycolysis and gluconeogenesis, citric acid cycle (TCA cycle), and ascorbate and aldarate metabolism. In this paper, 75 genes of the enzymes related to organic acid metabolic pathways were screened, and these enzymes included PEPC, MDH, ME, CS, IDH and ACO. Ten unigenes were selected to confirm by real-time PCR, and the linear regression between the RNA-Seq results and real-time PCR data was significant ( r = 0.8637). In addition, the expression of PEPC and ACO genes was consistent with the content of citric acid, the expression of the CS gene increased with time, and the change in expression of the MDH gene was similar to that of the malic acid content, while the expression of the ME gene showed an opposite trend. Therefore, it was possible to regulate acid accumulation in pulp by regulating the expression of key genes related to pathways such as the TCA cycle, and then the comprehensive fruit quality was regulated.

Exogenous GABA improves the resistance of apple seedlings to long-term drought stress by enhancing GABA shunt and secondary cell wall biosynthesis.

Drought stress is an important factor limiting apple production. γ-Aminobutyric acid (GABA) exists widely in plants and participates in the response to abiotic stress as a metabolite or signaling molecule. The role of exogenous GABA in apple plants, response to long-term drought stress remains unclear. Our study confirmed that exogenous GABA affects the drought resistance of apple plants under long-term drought stress. We found that 1mM exogenous GABA improved the resistance of apple seedlings to long-term drought stress. The plants showed better growth, less reactive oxygen radical accumulation, less damage to cell membranes and greater active photosynthetic capacity. Under long-term drought stress, exogenous GABA facilitated GABA shunt, resulting in more accumulation of organic acids, namely citric acid, succinic acid and malic acid, in roots and stems of apple seedlings. In addition, exogenous GABA upregulated the expression of cellulose-related genes and lignin-related genes, and activated secondary cell wall-related transcription factors to synthesize more cellulose and lignin. A multiple factorial analysis confirmed that the GABA shunt and the biosynthesis of cellulose and lignin substantially contributed to the growth of apple seedlings with the application of exogenous GABA under long-term drought stress. Our results suggested that exogenous GABA improved the resistance of apple seedlings to long-term drought stress by enhancing GABA shunt and secondary cell wall biosynthesis.

Spermine-mediated metabolic homeostasis improves growth and stress tolerance in creeping bentgrass (Agrostis stolonifera) under water or high-temperature stress.

Plants have developed diverse defense strategies to reduce the detrimental effects of a wide range of environmental stresses. The objectives of this study were to explore the function of spermine (Spm) on mediating growth and physiological changes in water homeostasis, photosynthetic performance, and oxidative damage and to further examine the regulatory mechanism of Spm on global metabolites reprogramming and associated metabolic pathways in horticultural creeping bentgrass (Agrostis stolonifera) under water and heat stresses. The 21-days-old plants were pretreated with or without 100 μM Spm for 3 days and then subjected to water stress (17% polyethylene glycol 6000), high-temperature stress (40/35°C, day/night), or normal condition (control without water stress and heat stress) for 18 days. Results demonstrated that exogenous application of Spm could significantly increase endogenous polyamine (PAs), putrescine (Put), spermidine (Spd), and Spm contents, followed by effective alleviation of growth retardant, water imbalance, photoinhibition, and oxidative damage induced by water and heat stress. Metabolites' profiling showed that a total of 61 metabolites were differentially or commonly regulated by Spm in leaves. Spm upregulated the accumulation of mannose, maltose, galactose, and urea in relation to enhanced osmotic adjustment (OA), antioxidant capacity, and nitrogen metabolism for growth maintenance under water and heat stress. Under water stress, Spm mainly induced the accumulation of sugars (glucose-1-phosphate, sucrose-6-phosphate, fructose, kestose, maltotriose, and xylose), amino acids (glutamic acid, methionine, serine, and threonine), and organic acids (pyruvic acid, aconitic acid, and ketoglutaric acid) involved in the respiratory pathway and myo-inositol associated with energy production, the ROS-scavenging system, and signal transduction. In response to heat stress, the accumulation of alanine, glycine, gallic acid, malic acid, or nicotinic acid was specifically enhanced by Spm contributing to improvements in antioxidant potency and metabolic homeostasis. This study provides novel evidence of Spm-induced,tolerance to water and heat stresses associated with global metabolites reprogramming in favor of growth maintenance and physiological responses in horticultural plants.

Shock loads change the resistance, resiliency, and productivity of anaerobic co-digestion of municipal sludge and fats, oils, and greases

Accidental organic overloading (shock loading) is a common cause of failure in the anaerobic co-digestion of fats, oils, and greases (FOG). Nonetheless, questions still remain about how shock loads alter an anaerobic digester's biogas productivity and response to future organic overloads. To address this knowledge gap, this study utilized short increases in OLR, or shock loads, to adapt one reactor to FOG co-digestion and compare its response to that of a non-adapted digester tested at similar organic loads. A long-term study was also conducted where sequential shock events and disturbance-to-failure events (with organic loading rates ranging from 2.5 to 9.0 g VS/L/d) were employed to study their effects on reactor stability and performance. When exposed to moderate and large shock loads (3.0 and 9.0 g VS/L/d, respectively), the anaerobic digester previously exposed to FOG shock loads had greater levels of resistance and resiliency. For a moderate shock, it took the non-adapted reactor 29.8, 43, 44, and 19 days longer than the adapted reactor to recover to the baseline levels for methane content, organic acids (OA), pH, and mcrA concentrations, respectively. For a large shock, the adapted and non-adapted reactors saw more similar recovery times with the non-adapted reactor requiring an additional 11, 18, 19, and 0 days longer than the adapted reactor to recover to baseline levels for methane content, OA, pH, and mcrA concentrations, respectively. However, exposure to successive large shock loads decreased the anaerobic digester's resistance and resilience. The length of time it took for the organic acid accumulation and methane content values to return to their pre-shock values generally increased with each successive large shock load. For OA, the reactor required 35, 39, and 43 days to recover from the first, second, and third large shocks, respectively, while the methane content recovery times were 27.5, 26.5, and 34.5 days for the same shock periods. Thus, this work demonstrates that there is a tipping point in which FOG shock loads, whether intentional or accidental, go from improving the overall robustness of an anaerobic digester to significantly deteriorating its overall performance.