Expression Of Phenylalanine Ammonia-lyase Research Articles

Elicitation of salicylic acid and methyl jasmonate provides molecular and physiological evidence for potato susceptibility to infection by Erwinia carotovora subsp. carotovora

Among the range of severe plant diseases, bacterial soft rot caused by Erwinia carotovora is a significant threat to crops. This study aimed to examine the varying response patterns of distinct potato cultivars to the influence of E. carotovora. Furthermore, it seeks to highlight the potential role of salicylic acid (SA) and methyl jasmonate (MeJA) in stimulating the antioxidant defence system. We collected eight bacterial isolates from diseased and rotted tubers which were morphologically and physiologically identified as E. carotovora subsp. carotovora. We conducted a greenhouse experiment to analyse the antioxidant responses of three different potato cultivars (Diamont, Kara, and Karros) at various time intervals (2, 4, 6, 8, 12, and 24 h) after bacterial infection (hpi). We assessed the extent of disease damage by applying a foliar spray of 0.9 mM salicylic acid (SA) and 70 μM methyl jasmonate (MeJA). Inoculating with Ecc led to an increase in total phenolic levels, as well as the activities and gene expression of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POX) as time progressed. Additionally, the application of SA and MeJA resulted in a further increase relative to the diseased treatments. The Karros cultivar, unlike the Diamont and Kara cultivars, demonstrated the highest expression levels of PAL, PPO and POX through inoculation, reflecting its higher levels of activity and resistance. Furthermore, the genetic response of potato cultivars to infection at 0 hpi varied depending on their susceptibility. The examination of the rate of PAL activity upregulation following SA or MeJA stimulation clarifies the cultivars' susceptibility over time. In conclusion, the study identified E. carotovora subsp. carotovora as the most virulent isolate causing soft rot disease in potato tubers. It further revealed that the Karros cultivar displayed superior resistance with high activities and gene expression of PAL, PPO and POX, while the cv. Diamont exhibited sensitivity. Additionally, foliar exposure to SA and MeJA induced antioxidant responses, enhancing the potato plants' resistance against Ecc pathogenesis and overall plant defence.

Integrated transcriptomic and metabolomic analyses reveals anthocyanin biosynthesis in leaf coloration of quinoa (Chenopodium quinoa Willd.)

BackgroundQuinoa leaves demonstrate a diverse array of colors, offering a potential enhancement to landscape aesthetics and the development of leisure-oriented sightseeing agriculture in semi-arid regions. This study utilized integrated transcriptomic and metabolomic analyses to investigate the mechanisms underlying anthocyanin synthesis in both emerald green and pink quinoa leaves.ResultsIntegrated transcriptomic and metabolomic analyses indicated that both flavonoid biosynthesis pathway (ko00941) and anthocyanin biosynthesis pathway (ko00942) were significantly associated with anthocyanin biosynthesis. Differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) were analyzed between the two germplasms during different developmental periods. Ten DEGs were verified using qRT-PCR, and the results were consistent with those of the transcriptomic sequencing. The elevated expression of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), 4-coumarate CoA ligase (4CL) and Hydroxycinnamoyltransferase (HCT), as well as the reduced expression of flavanone 3-hydroxylase (F3H) and Flavonol synthase (FLS), likely cause pink leaf formation. In addition, bHLH14, WRKY46, and TGA indirectly affected the activities of CHS and 4CL, collectively regulating the levels of cyanidin 3-O-(3’’, 6’’-O-dimalonyl) glucoside and naringenin. The diminished expression of PAL, 4CL, and HCT decreased the formation of cyanidin-3-O-(6”-O-malonyl-2”-O-glucuronyl) glucoside, leading to the emergence of emerald green leaves. Moreover, the lowered expression of TGA and WRKY46 indirectly regulated 4CL activity, serving as another important factor in maintaining the emerald green hue in leaves N1, N2, and N3.ConclusionThese findings establish a foundation for elucidating the molecular regulatory mechanisms governing anthocyanin biosynthesis in quinoa leaves, and also provide some theoretical basis for the development of leisure and sightseeing agriculture.

Epigallocatechin-3-gallate-induced tolerance to cadmium stress involves increased flavonoid synthesis and nutrient homeostasis in tomato roots

Cadmium (Cd) is a toxic heavy metal, increasingly accumulating in the environment and its presence in various environmental compartments represents a significant risk to human health via the food chain. Epigallocatechin-3-Gallate (EGCG) is a prominent secondary metabolite, which can safeguard plants from biotic and abiotic stress. However, the role of EGCG in flavonoid synthesis, nutrient acquisition and reactive oxygen species (ROS) metabolism under Cd stress remains unclear. Here, we examined the effects of EGCG and Cd treatment on leaf photochemical efficiency, cell ultrastructure, essential element acquisition, antioxidant system, and secondary metabolism in tomato (Solanum lycopersicum L.). The results showed that O2•−, H2O2, and malondialdehyde levels increased after Cd treatment, but Fv/Fm decreased significantly, suggesting that Cd induced oxidative stress and photoinhibition. However, EGCG mitigated the adverse effects of Cd-induced phytotoxicity in both the roots and leaves. A decrease in ROS accumulation under EGCG + Cd treatment was mainly attributed to the significant enhancement in antioxidant enzyme activity, flavonoid content, and PHENYLALANINE AMMONIA-LYASE expression in roots. Moreover, EGCG reduced Cd content but increased some essential nutrient contents in tomato plants. Transmission electron microscopy-based observations revealed that EGCG treatment safeguards leaf and root cell ultrastructure under Cd stress. This implies that tomato plants subjected to Cd stress experienced advantageous effects upon receiving EGCG treatment. The present work elucidated critical mechanisms by which EGCG induces tolerance to Cd, thereby providing a basis for future investigations into environmentally sustainable agricultural practices in areas contaminated with heavy metals, for utilizing naturally occurring substances found in plants.

The expression of lignin biosynthesis genes during plant development and effects of downregulated cinnamyl alcohol dehydrogenase (CAD) gene in bahiagrass (Paspalum notatum Flügge)

AbstractBahiagrass (Paspalum notatum Flügge) is a warm‐season grass where high lignin content limits its forage quality, negatively affecting animal performance. To create a new breeding method by genome editing, isolation and characterization of lignin biosynthesis genes and identification of their molecular relationships are essential. The caffeic acid O‐methyltransferase (COMT) and cinnamyl alcohol dehydrogenase (CAD) cDNA clones were isolated from bahiagrass, and their protein sequences showed high similarity to other C4 monocot species through phylogenetic analysis. Gene expression analysis of phenylalanine ammonia‐lyase (PAL), COMT and CAD, involved in crucial stages of lignin biosynthesis and lignin content, was conducted at different plant developmental stages. The highest gene expression levels of these genes were observed in the vegetative (V) and early reproductive stages, while the lignin content increased until the middle reproductive stage and remained constant thereafter. Additionally, to further understand the molecular relationships in lignin biosynthesis, the effect of CAD downregulation was analyzed in transgenic bahiagrass lines introduced with sorghum CAD antisense and RNAi vector obtained from a previous report. This led to a reduced lignin content and affected the expression of PAL and COMT working upstream of CAD. In the V stage, PAL expression was lower in transgenic lines compared to wild type (WT), while COMT expression showed no significant differences. However, PAL and COMT expression of transgenic lines in the middle reproductive stage (R2) was significantly higher than in the WT. These findings suggest that the downregulation of CAD gene expression affects PAL and COMT expression and induces a feedback system in the R2 stage. Lignin content influenced the phenotype of the transgenic plants with significantly reduced lignin, exhibiting a dwarf phenotype with shorter plant heights. The findings of this study can be applied to genome editing for the development of practical new breeding materials with improved digestibility in bahiagrass.

Adaptive response of flavonoids in Robinia pseudoacacia L. affected by the contamination of cadmium and elevated CO2 to arbuscular mycorrhizal symbiosis

As a key component in non-enzyme resistance system, flavonoids play a crucial role in the plant growth and defenses, which are significantly affected by biotic and abiotic factors such as fungi, bacteria, viruses, heavy metals, and atmospheric CO2. Arbuscular mycorrhizal fungi (AMF) play an important role in enhancing plant tolerance to adverse environments, which can significantly affect the synthesis of flavonoids by forming mycorrhizal symbionts with plant roots. However, few studies explored the combined effects of AMF, elevated CO2, and heavy metals on flavonoids in plants. Here, we investigated the adaptive response of flavonoids accumulation in Robinia pseudoacacia L. seedlings affected by the contamination of cadmium (Cd) and elevated CO2 to arbuscular mycorrhizal symbiosis. The results showed that G. mosseae decreased (p < 0.05) Cd content in leaves by 62.2% under elevated CO2. Moreover, G. mosseae colonization led to significant decreases in robinin, quercetin, kaempferol and acacetin by 17.4%, 11.1%, 15.5% and 23.1% under elevated CO2 + Cd, respectively. Additionally, G. mosseae down-regulated (p < 0.05) expression levels of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) genes under elevated CO2 + Cd, and CHS and uridine diphosphate flavonoid glucosyltransferase (UFGT) activities decreased (p < 0.05). Quercetin, kaempferol and acacetin showed positive (p < 0.05) correlation with PAL and CHS genes expression and PAL, CHS, and UFGT activities. Cadmium, C/N ratio, carotenoids, leaf biomass, total chlorophyll, P, and starch in leaves and G. mosseae colonization rate in roots influenced (p < 0.05) flavonoids content. Overall, G. mosseae reduced flavonoids synthesis by down-regulating gene expression levels and activities of key enzymes under elevated CO2 + Cd. The results improved our understanding of the regulation of AMF on non-enzymatic resistance of plants grown in heavy metal-contaminated soils under increasing atmospheric CO2 scenarios.

Transcriptome and metabolic survey disclose the mode of action of static and dynamic low oxygen postharvest storage strategies to prevent the onset of superficial scald disorder in fruit of ‘Granny Smith’ apple cultivar

To preserve quality features and ensuring availability of fresh fruit on the market, apples need to be stored after harvest. The low temperature applied during storage, beside avoiding important fruit loss, can also promote the development of serious chilling injury disorders, such as superficial scald. One of the strategies largely employed to prevent the development of this phenomenon is the control of the storage atmosphere by lowering down the oxygen concentration. In this work, a multifaceted survey was carried out to investigate transcriptome variation together with three categories of metabolites (phenolics, lipids and volatile organic compounds ) in fruit of ‘Granny Smith’ apple cultivar stored in both static and dynamic controlled hypoxia atmosphere for five and seven months, respectively. The global transcriptome survey identified a core set of differentially expressed genes in three main functional groups, revealing as the duration of storage had an important effect in the coordination of gene expression. The effect of the length of storage was furthermore highlighted by the DEG-network analysis that identified a distinct number and type of transcriptomic hubs. Samples characterized by the development of superficial scald were distinguished by a higher concentration of chlorogenic acid and a higher expression of phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) in a time-dependent fashion. The prevention of this disorder was instead related to distinctive re-programming events, involving the accumulation of specific antioxidant types of metabolites, very long chain fatty acids (VLCFAs) and the expression of genes coordinating a hypoxia acclimation process, such as RAP2-like and plant cysteine oxidase (PCO).

Drought stress-responsive abscisic acid and salicylic acid crosstalk with the phenylpropanoid pathway in soybean seeds.

Crosstalk between hormones and secondary metabolites regulates the interactions between plants and stress. However, little is known about the effects of hormone crosstalk on the concentration of flavonoids in seeds. In this study, we identified abscisic acid (ABA) as a negative regulator of flavonoid accumulation in soybean seeds under drought-stress conditions. Alterations in flavonoid accumulation at several intensities of water stress, followed by a recovery period, were measured during the soybean seed-filling stage. Low soil moisture (SM 10%) significantly decreased the total flavonoid content in seeds. The decline in flavonoid content was proportional to the severity of drought stress and was dependent on the activities of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS), two key phenylpropanoid pathway enzymes. The expression of phenylalanine ammonia-lyase 1 (GmPAL1), chalcone isomerase 1A (GmCHI1A), and chalcone synthase 8 (GmCHS8) was associated with phenolic and flavonoid accumulation in soybean seeds of plants subjected to drought stress. Interestingly, the expression levels of GmCHS8 were highly correlated with flavonoid levels under drought stress and water recovery conditions. Cinnamic acid, which is a biosynthesis precursor shared by both phenylpropanoid metabolism and salicylic acid (SA) biosynthesis, decreased under drought stress conditions. Notably, exogenous ABA suppressed the expression of GmPAL1, which encodes the first rate-limiting enzyme in the phenylpropanoid biosynthesis pathway and affects downstream products such as SA and flavonoids. In conclusion, drought stress altered the phenylpropanoid-derived compounds, at least with regard to flavonoid and SA accumulation in seeds, which was regulated by antagonistic interactions with ABA.

Laboratory evolution of Synechocystis sp. PCC 6803 for phenylpropanoid production

Cyanobacteria are promising as a biotechnological platform for production of various industrially relevant compounds, including aromatic amino acids and their derivatives, phenylpropanoids. In this study, we have generated phenylalanine resistant mutant strains (PRMs) of the unicellular cyanobacterium Synechocystis sp. PCC 6803, by laboratory evolution under the selective pressure of phenylalanine, which inhibits the growth of wild type Synechocystis. The new strains of Synechocystis were tested for their ability to secrete phenylalanine in the growth medium during cultivation in shake flasks as well as in a high-density cultivation (HDC) system. All PRM strains secreted phenylalanine into the culture medium, with one of the mutants, PRM8, demonstrating the highest specific production of 24.9 ± 7 mg L−1·OD750−1 or 610 ± 196 mg L−1 phenylalanine after four days of growth in HDC. We further overexpressed phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) in the mutant strains in order to determine the potential of PRMs for production of trans-cinnamic acid (tCA) and para-coumaric acid (pCou), the first intermediates of the plant phenylpropanoid pathway. Productivities of these compounds were found to be lower in the PRMs compared to respective control strains, except for PRM8 under HDC conditions. The PRM8 background strain in combination with PAL or TAL expression demonstrated a specific production of 52.7 ± 15 mg L−1·OD750−1tCA and 47.1 ± 7 mg L−1·OD750−1pCou, respectively, with a volumetric titer reaching above 1 g L−1 for both products after four days of HDC cultivation. The genomes of PRMs were sequenced in order to identify which mutations caused the phenotype. Interestingly, all of the PRMs contained at least one mutation in their ccmA gene, which encodes DAHP synthase, the first enzyme of the pathway for aromatic amino acids biosynthesis. Altogether, we demonstrate that the combination of laboratory-evolved mutants and targeted metabolic engineering can be a powerful tool in cyanobacterial strain development.

Subcellular damages of pathogenic fungi combined with gene expression analysis reveals mechanisms that cold plasma controlling apricot disease

Dielectric barrier discharge (DBD) plasma technology has proven effective in controlling postharvest fungus in fruits and vegetables. However, its mechanism of action is rarely reported. In this study, DBD technology was investigated to inhibit apricot diseases under the conditions of shelf simulation, and its mechanism was analysed. Apricot fruits and pathogenic fungal spores were treated with DBD of different voltage intensities（fruits: 80 kV, 90 kV, 100 kV; spores: 80 kV, 100 kV, 120 kV). Experimental data showed that DBD plasma treatment significantly reduced the microbial biomass on the surface of apricot fruit and inhibit Rhizopus oryzae and Alternaria tenuissima. Rhizopus oryzae and Alternaria tenuissima's spore germination decreased by 74.7% and 82.0%, respectively, after 40 s of processing with 100 kV DBD treatment. To investigate DBD plasma's antibacterial mechanism, deoxyribonucleic acid damage and the morphological characteristics of fungal spores were determined; this indicated that DBD plasma treatment resulted in nuclear degradation and cell deformation. In addition, DBD treatment enhanced apricots' expression of phenylalanine ammonia-lyase 1 (PAL1), aldehyde dehydrogenase 2B7 (ALDH2B7) and GDP-L-galactose phosphorylase (VTC2), delayed disease and improved quality under shelf storage conditions. The results demonstrated that DBD plasma treatment could control the primary diseases of apricot fruit and enhance the quality by destroying microbial spores and activating the disease-resistant genes of the fruit.

Endogenous salicylic acid mediates melatonin-induced chilling-and oxidative-stress tolerance in harvested kiwifruit

Phytohormone melatonin (MT) has shown promise in alleviating chilling injury (CI) in kiwifruit; however, the performance and mechanism remain largely unknown. In this study, the effect of pretreatment of MT at concentration of 0.05 mM on CI in ‘Xuxiang’ kiwifruit during storage at 1 °C for 90 d was investigated, as well as the implication of endogenous salicylic acid (SA) in MT-induced chilling-and oxidative-stress tolerance. MT pretreatment protected kiwifruit against CI, as figured out by lower CI index, firmness loss and soluble solids accumulation and better pulp appearance than those in control fruit. MT pretreatment stimulated endogenous SA generation by activating the gene expression of phenylalanine ammonia lyase (PAL) and activity of PAL and benzoic acid-2-hydroxylase, therefore up-regulated SA-responsive pathogenesis-related gene 1 expression, and provoked kiwifruit defense response to chilling stress. Moreover, reactive oxygen species in MT-pretreated fruit were neutralized by evaluating endogenous MT, ascorbic acid and glutathione contents and superoxide dismutase, catalase and ascorbate peroxidase activity, thus reducing membrane damage. However, such positive regulations of MT on kiwifruit were counteracted to varying extent by pretreatment of the combination of paclobutrazol PAC, a SA biosynthesis inhibitor, with MT. These findings indicated a mediating role of endogenous SA in chilling-and oxidative-stress tolerance in kiwifruit induced by MT pretreatment that could be operative by evoking defense response to chilling stress and enhancing antioxidative protection.

UV-B radiation enhances isoflavone accumulation and antioxidant capacity of soybean calluses.

Isoflavones are a class of flavonoids that belong to a large family of polyphenols and synthesized predominantly in legume, and they play important roles including acting as antioxidant, preventing osteoporosis, reducing the risk of atherosclerosis, and protecting against cardiovascular disease. This study focused on the accumulation and synthetic metabolism of isoflavone in soybean hypocotyl and cotyledon calluses under UV-B radiation. The results showed that UV-B radiation significantly up-regulated the gene expression of phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), chalcone ketone synthase (CHS), chalcone isomerase (CHI), and isoflavone synthase (IFS), and enhanced their activity in soybean hypocotyl and cotyledon calluses. As a result, isoflavones content increased by 21.23 and 21.75% in soybean hypocotyl and cotyledon calluses, respectively. Among the isoflavones produced, malonyldaidzin was the dominant one in hypocotyl callus, while malonylglycitin and daidzein were the main isoflavones in cotyledon calluses. This study revealed that UV-B radiation induced isoflavone accumulation in soybean calluses, which could be an efficient strategy to improve the nutritional value of food and produce high levels of bioactive secondary metabolites.

Lignification in Zinnia (Zinnia elegans Jacq.) Stem Sections of Different Age: Biochemical and Molecular Genetic Traits

Lignification of the stem in zinnia provides its mechanical properties due to xylem formation, which depends on the stage of plant development and is responsible for the transport of water and minerals. The study was aimed at the lignin deposition, anatomical traits, biochemical markers of lignification, as well as the genetic regulation of this process in zinnia stem cross sections of different age during their radial growth. The anatomical traits were assessed on cross sections. The content of lignin (Cysteine-assisted sulfuric method (CASA) and the thioglycolic acid (TGA) methods), the spectrum of phenolics (by thin layer chromatography (TLC)), the total activity and the variety of class III peroxidases were determined. The expression level of genes regulating phenylpropanoids and lignin biosynthesis were assessed. We suggest that time-specific and organ-specific lignification is determined by the metabolism of phenolic compounds and depends on the expression of genes of the phenylpropanoid pathway. It was shown that in the hypocotyl, during xylem ring formation, lignification was associated with increased expression of phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) genes responsible for the early stages of the phenylpropanoid pathway, and with the rise of class III peroxidases activity, including cationic isoforms. This caused increased content and diversity of phenolics in mature hypocotyl. In epicotyl, which is younger than the hypocotyl, the proportion of ferulic acid among phenolics increased, which could be considered as a marker of lignification in it. The high expression level of CAD and the activity of peroxidases, including anionic isoforms, led to accumulation of lignin. Thus, the hypocotyl and epicotyl, being characterized by different ages, differed in spectrum of phenolics, isoforms of class III peroxidases, expression of the PAL, cinnamate 4-hydroxylase (C4H), peroxidases III class (PRX), and laccase (LAC) genes, and lignin content.

Enhanced Antioxidant and Anticancer Potential of Artemisia carvifolia Buch Transformed with rol A Gene.

Secondary metabolites have been shown to possess a range of biological functions. Flavonoids, due to their ability to scavenge ROS, are famous antioxidants. The plants of Artemisia species are rich sources of flavonoids; however, the amount of these metabolites is less. In the current study, the flavonoid content was detected and then enhanced by genetically modifying the Artemisia carvifolia Buch with Agrobacterium tumefaciens strain GV3101 carrying rol A gene. The transformation of rol A gene was confirmed with PCR and the gene copy number was confirmed by Southern blot analysis. The HPLC analysis revealed the presence of catechin (3.19 ug/mg DW) and geutisic acid (2.22 ug/mg DW) in transformed plants, unlike wild-type plants. In transformed plants, all detected flavonoids (vanillic acid, rutin, catechine, gallic acid, syringic acid, caffeic acid, coumaric acid, geutisic acid, ferulic acid, and cinnamic acid) were increased up to several folds. Real-time qPCR revealed the higher expression levels of the genes for flavonoid biosynthesis enzymes phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) in plants transformed with rol A genes, as the expression levels were increased up to 9-20-fold and 2-6-fold, respectively. The rol A transgenic lines T3 and T5 carrying two copies of rol A gene, particularly showed higher expression of both PAL and CHS gene, with the highest expression in T3 line. The transgenic lines demonstrated an average increase of 1.4-fold in the total phenolic content and 1-2-fold in the total flavonoid content as compared to wild-type plants. Total antioxidant capacity and total reducing power were increased up to an average of 1-2-fold and 1.5-2-fold respectively, along with increased free radical scavenging ability. Furthermore, the rol A gene transgenics were found to have much greater cytotoxic capacity than the A. carvifolia wild-type plant against the MCF7, HeLA, and HePG2 cancer cell lines. Current findings show that the rol A gene effectively increases the flavonoid content of A. carvifolia Buch, boosting the plant's capacity as an antioxidant and an anticancer. This is the first-ever report, demonstrating the genetic transformation of Artemisia carvifolia Buch with rol A gene.

Effects of Water Stress on Resveratrol Accumulation and Synthesis in ‘Cabernet Sauvignon’ Grape Berries

Resveratrol (3, 4′, 5 trihydroxy stilbene) is a natural phytoalexin produced by plants in response to biotic and abiotic stresses. It is well known for its cardio-protective, anticarcinogenic, and antioxidant properties. This study characterized physiological and molecular changes in resveratrol synthesis exposed to two levels of water stress at distinct grape berry developmental stages. Physiological data were measured to assess the berry quality. We used high-performance liquid chromatography to study enzyme activity and qRT-PCR to assess the expression levels of genes involved in resveratrol synthesis. The berry development was suppressed under water stress, while the content of total polyphenol, especially resveratrol was enhanced. Related enzymes and genes regulate the changes in resveratrol in plants. Water stress improved the enzyme activities of PAL (phenylalanine ammonia-lyase) and STS (stilbene synthase) after veraison. Moreover, the transcription factors VvMYB14, VvMYB15 and resveratrol synthesis-related genes are also changed. Expression of Vv4CL and VvMYB15 were upregulated during the pre-reversion stage, whereas VvPAL and VvSTS increased throughout development. As the co-substrate of VvSTS, VvCHS decreased during the berry development. Our study demonstrates that water stress regulates resveratrol synthesis through enzymatic activities and the gene expression of PAL and STS.

Stress response of fresh-cut potatoes to laser irradiation before processing can prevent discoloration and maintain overall quality

Browning is accepted as a main factor affecting quality of fresh cut products. Physical treatments maintaining quality of fresh-cut products have been recently considered by consumer safer than chemical treatments. This study investigated whether preprocess diode laser irradiation can improve the physicochemical quality of fresh-cut potatoes. Laser irradiation at a 450-nm wavelength for 30 min prevented the browning of potato slices during short-term storage at 25 °C. Compared with no treatment, preprocess laser irradiation preserved the appearance and whiteness and inhibited browning and delayed weight loss in potato slices when refrigerated at 4 °C for 96 h. The increases in the total phenol concentration and phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) activities of fresh-cut potatoes were diminished after laser irradiation. Moreover, the laser irradiation also enhanced antioxidant activities in the samples. The expression of PAL, PPO and POD genes was suppressed by the laser treatment. Therefore, the laser irradiation at 450 nm wavelength for 30 min effectively eliminates discolouration and improves quality of sliced potatoes during cold storage.

Inoculation of Pochonia chlamydosporia triggers a defense response in tomato roots, affecting parasitism by Meloidogyne javanica

Pochonia chlamydosporia is a soil-dwelling fungus and biological control agent of nematodes, active ingredient in commercial bionematicides. The fungus is also endophytically associated with the roots of several plant species, promoting their growth and inducing systemic resistance. In this study, different pathways and tomato defense metabolites were studied to identify mechanisms induced by P. chlamydosporia that contribute to the control of Meloidogyne javanica, at early and late developmental stages. Some defense responses activated by the fungus appeared related to the nematode life cycle. Among the evaluated biochemical analysis, root colonization of P. chlamydosporia showed an increase in the concentration of phenolic compounds, such as chlorogenic acid. In addition, the expression of some host plant genes was also modified. The interaction of the fungus with roots parasitized by M. javanica resulted in the highest expression of Phenylalanine Ammonia-Lyase (PAL), Chalcone synthase (LECHS 2), and Protease Inhibitor (PI1) genes at 24 days post-inoculation. At the second sampling time (44 days), there was an increase in the expression of the Respiratory Burst Oxidase Homolog (RBOH) gene. Fungus reduced the expression of the ACC-oxidase and Pathogenesis-Related Proteins 1 (PR-1) genes in roots. Moreover, P. chlamydosporia inoculation changed metabolites and phytohormone profiles of the gall formed by M. javanica. Plant defense response appeared to involve the jasmonic acid and phytosphingosine cascades. With this analysis, it was possible to propose new molecular mechanisms induced by the fungus that contribute to the control of M. javanica.

Controlling effect and mechanism of burdock fructooligosaccharide against Alternaria fruit rot in blueberry during postharvest

Burdock fructooligosaccharide (BFO), a naturally occurring elicitor derived from the roots of Arctium lappa, can promote postharvest disease resistance in grapes, apples, bananas, and so forth. However, its controlling effect and mechanism against postharvest diseases caused by Alternaria tenuissima in blueberries are unclear. This study showed that BFO treatment restrained the postharvest development of Alternaria fruit rot in blueberries. In the initial stage of fruit storage, BFO treatment induced a hydrogen peroxide burst promoting the blueberry resistance response against A. tenuissima invasion. In addition, BFO treatment increased the activities and gene expression of antioxidant enzymes and pathogenesis-related proteins, such as superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, chitinase, and β-1,3-glucanase, thereby enhancing the fruit resistance to pathogens. The increased activities and gene expression of phenylalanine ammonia-lyase, 4-coumarate CoA ligase, and cinnamate 4-hydroxylase in blueberries were accompanied by increased levels of total phenolics, flavonoids, anthocyanin, and lignin, indicating the activation of the phenylpropanoid pathway. In conclusion, BFO can be a promising elicitor to control the Alternaria fruit rot in blueberries.

Nitric oxide mediates melatonin-induced isoflavone accumulation and growth improvement in germinating soybeans under NaCl stress

The involvement of nitric oxide (NO) in exogenous melatonin (MT)-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans was investigated in this study. The results demonstrated that MT increased the activity of nitrate reductase (NR) and upregulated the relative expression of NR1, NR2, and nitric oxide synthase1, which subsequently led to an increase in NO content. MT and sodium nitroprusside (SNP, as an NO donor) markedly increased isoflavone content by enhancing the activities of cinnamic acid 4-hydroxylase (C4H) and phenylalanine ammonia lyase (PAL), and by upregulating gene expression of C4H, Isoflavone synthase, PAL, and Chalcone isomerase 1A, which are involved in isoflavone biosynthesis. Moreover, MT, as well as SNP, improved the growth and biomass of NaCl-treated soybeans by increasing the activities of superoxide dismutase, catalase, and peroxidase, and reducing the accumulation of H2O2 and O2•− in soybeans under NaCl stress. These MT-induced responses were entirely reversed by the supply of 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, a specific scavenger of NO), which in turn considerably decreased endogenous NO content. These results suggest that NO acts as an important downstream signal molecule, mediating MT-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans.

MsMYB741 is involved in alfalfa resistance to aluminum stress by regulating flavonoid biosynthesis.

Aluminum (Al) toxicity severely restricts plant growth in acidic soils (pH < 5.0). In this study, an R2R3-MYB transcription factor (TF) gene, MsMYB741, was cloned from alfalfa. Its function and gene regulatory pathways were studied via overexpression and RNA interference of MsMYB741 in alfalfa seedlings. Results showed that root elongation increased as a result of MsMYB741 overexpression (MsMYB741-OE) and decreased with MsMYB741 RNA interference (MsMYB741-RNAi) in alfalfa seedlings compared with the wild-type under Al stress. These were attributed to the reduced Al content in MsMYB741-OE lines, and increased Al content in MsMYB741-RNAi lines. MsMYB741 positively activated the expression of phenylalanine ammonia-lyase 1 (MsPAL1) and chalcone isomerase (MsCHI) by binding to MYB and ABRE elements in their promoters, respectively, which directly affected flavonoid accumulation in roots and secretion from root tips in plants under Al stress, eventually affecting Al accumulation in alfalfa. Additionally, MsABF2 TF directly activated the expression of MsMYB741 by binding to the ABRE element in its promoter. Taken together, our results indicate that MsMYB741 transcriptionally activates MsPAL1 and MsCHI expression to increase flavonoid accumulation in roots and secretion from root tips, leading to increased resistance of alfalfa to Al stress.

PpMYB308 is involved in Pichia guilliermondii-induced disease resistance against Rhizopus rot by activating the phenylpropanoid pathway in peach fruit

Pichia guilliermondii has been shown to control fungal decay in various harvested fruits by inducing disease resistance, but the transcriptional regulatory mechanism remains unclear. In our study, P. guilliermondii treatment induced resistance against soft rot caused by Rhizopus stolonifer in peach fruit, as shown by the reduced disease incidence and severity, increased enzyme activities and gene expression of phenylalanine ammonia-lyase (PAL) and 4-coumarate-CoA ligase (4CL), and promoted the accumulation of total phenolics, total flavonoids and the main individual phenolic compounds (neochlorogenic acid, chlorogenic acid, gallic acid, and rutin). In addition, P. guilliermondii induced the expression of PpMYB308, which was identified as a nucleus‐localized transcriptional activator of PpPAL1 and Pp4CL5 by binding to the MREs (MYB recognition elements). Moreover, the transient overexpression of PpMYB308 in peach fruit enhanced the expression of PpPAL1 and Pp4CL5 and reduced disease incidence and severity. Therefore, the results indicate that PpMYB308 is involved in P. guilliermondii-induced disease resistance against R. stolonifer by activating the phenylpropanoid pathway.