Sodium silicate accelerates suberin accumulation at wounds of potato tuber by inducing phenylpropanoid pathway and fatty acid metabolism during healing.

Although soluble silicate was reported to accelerate wound healing in muskmelon fruit through encouraging the deposition of lignin or free fatty acids, whether sodium silicate affects the biosynthesis, cross-linking and transport of suberin monomers during potato wound healing remains unknown. In this study, sodium silicate upregulated the expression and activity of 4-coumarate: coenzyme A ligase (4CL), phenylalanine ammonia lyase (PAL), and promoted the synthesis of phenolic acids (caffeic acid, p-coumaric acid, cinnamic acid, sinapic acid, and ferulic acid) in tuber wounds. Meanwhile, sodium silicate upregulated the expression of glycerol-3-phosphate acyltransferase (StGPAT), fatty acyl reductase (StFAR), long-chain acyl-CoA synthetase (StLACS), ß-ketoacyl-CoA synthase (StKCS), and cytochrome P450 (StCYP86A33), and thus increased the levels of α, ω-diacids, ω-hydroxy acids, and primary alcohols in wounds. Sodium silicate also induced the expression of ω-hydroxy acid/fatty alcohol hydroxycinnamoyl transferase (StFHT), ABC transporter (StABCG), and promoted the deposition of suberin in wound surface, hence reducing tuber disease index and weight loss during healing. Taken together, sodium silicate may accelerate suberin accumulation at potato tubers wound through inducing the phenylpropanoid pathway and fatty acid metabolism.

Regulation of sucrose metabolism, sugar transport and pentose phosphate pathway by PacC in apple fruit colonized by Penicillium expansum.

A critical transcription factor, PacC, modulates the expression of fungal pH signaling. Although PacC-mediated environmental pH has been reported to regulate the growth and pathogenicity of postharvest pathogens, the involvement of PacC in sucrose metabolism, sugar transport, and the pentose phosphate pathway (PPP) in different zones of decayed fruit remains unclear. Our work showed that the inoculation with a PePacC deletion strain of Penicillium expansum (ΔPePacC) accelerated sucrose catabolism and glucose and fructose accumulation in different zones of apple fruit. This was attributed to an increase in sucrose metabolism enzyme activities and up-regulation of the sugar transporter protein-related gene expression. Moreover, ΔPePacC inoculation increased the PPP-related enzyme activities and the levels of nicotinamide adenine dinucleotide phosphate (NADPH) and NADP+. In conclusion, PacC modulates sucrose metabolism, sugar transport, and the PPP in apple fruit by mediating dynamic changes in environmental pH, thereby enhancing fruit disease resistance.

Moldy odors in food - a review.

Food products are susceptible to mold contamination, releasing moldy odors. These moldy odors not only affect the flavor of food, but also pose a risk to human health. Moldy odors are a mixture of volatile organic compounds (VOCs) released by the fungi themselves, which are the main source of moldy odors in moldy foods. These VOCs are secondary metabolites of fungi and are synthesized through various biosynthetic pathways. Both the fungi themselves and environmental factors affect the release of moldy odors. This review summarized the main components of musty odors in moldy foods and their producing fungi. In addition, this review focused on the functions of moldy volatile organic compounds (MVOCs) and the biosynthetic pathways of the major MVOCs, and summarized the factors affecting the release of MVOCs as well as the detection methods. It expected to provide a basis for ensuring food safety.

Essential role of ABA signaling and related transcription factors in phenolic acid and lignin synthesis during muskmelon wound healing.

Abscisic acid (ABA) is a key phytohormone involved in wound healing in fruits and vegetables, while fluridone (FLD) is its synthetic inhibitor. However, it is unknown whether ABA signaling and downstream transcription factors are involved in the synthesis of phenolic acids and lignin monomers in muskmelon wounds, and the underlying mechanisms. In our study, exogenous ABA promoted endogenous ABA synthesis by increasing the levels of ß-carotenoid and zeaxanthin, activating 9-cis-epoxycarotenoid dioxygenase (NCED) and zeaxanthin epoxidase (ZEP), facilitated ABA signaling by increasing the expression levels of protein phosphatases type 2C (CmPP2C) and ABA-responsive element binding factors (CmABF), upregulated the expression levels of CmMYB1 and CmWRKY1, and ABA induced phenylpropanoid metabolism by activating phenylalanine ammonia-lyase (PAL), 4-coenzyme A ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD), which further increased the synthesis of phenolic acids and lignin monomers in muskmelon wounds during healing. Taken together, exogenous ABA induced phenylpropanoid metabolism and increased the synthesis of phenolic acid and lignin monomer in muskmelon wounds during healing, and may be involved in endogenous ABA synthesis and signaling and related transcription factors.

Preharvest spraying of phenylalanine activates the sucrose and respiratory metabolism in muskmelon wounds during healing.

Phenylalanine (Phe) accelerates fruit wound healing by activating phenylpropanoid metabolism. However, whether Phe affects sucrose and respiratory metabolism in fruit during wound healing remains unknown. In this research, we found that preharvest Phe spray promoted sucrose degradation and increased glucose and fructose levels by activating acid invertase (AI), neutral invertase (NI), sucrose synthase (SS) and sucrose phosphate synthase (SPS) on harvested muskmelons. The spray also activated hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), malate dehydrogenase (MDH), succinate dehydrogenase (SDH) and glucose-6-phosphate dehydrogenase (G6PDH). In addition, the spray improved energy and reducing power levels in the fruit. Taken together, preharvest Phe spray can provide carbon skeleton, energy and reducing power for wound healing by activating the sucrose metabolism, Embden-Meyerhof-Parnas (EMP) pathway, tricarboxylic acid (TCA) cycle and pentose phosphate (PPP) pathway in muskmelon wounds during healing, which is expected to be developed as a new strategy to accelerate fruit wound healing.

Bacterial-fungal crosstalk is defined by a fungal lactone mycotoxin and its degradation by a bacterial lactonase.

Bacteria, fungi, and mammals contain lactonases that can degrade the Gram-negative bacterial quorum sensing (QS) molecules N-acyl homoserine lactones (AHLs). AHLs are critical for bacteria to coordinate gene expression and pathogenicity with population density. However, AHL-degrading lactonases present variable substrate ranges, including degradation of the Pencillium expansum lactone mycotoxin patulin. We selected Erwinia spp. as our model bacteria to further investigate this interaction. We find both native apple microbiome Erwinia spp. and the fruit tree pathogen Erwinia amylovora to be inhibited by patulin. At patulin concentrations that inhibited E. amylovora growth, expression of E. amylovora lactonase encoded by EaaiiA was increased. EaAiiA demonstrated the ability to degrade patulin in vitro, as well, as in vivo where it reduced apple disease and patulin production by P. expansum. Fungal-bacterial co-cultures revealed that the E. amylovora Δeaaiia strain failed to protect apples from P. expansum infections, which contained significant amounts of patulin. Our results suggest that bacterial lactonase production can modulate the pathogenicity of P. expansum in response to the secretion of toxic patulin. IMPORTANCE: Chemical signaling in the microbial world facilitates the regulation of gene expression as a function of cell population density. This is especially true for the Gram-negative bacterial signal N-acyl homoserine lactone (AHL). Lactonases that deactivate AHLs have attracted a lot of attention because of their antibacterial potential. However, the involvement of these enzymes in inhibiting fungal pathogens and the potential role of these enzymes in bacterial-fungal interactions are unknown. Here, we find that a bacterial enzyme involved in the degradation of AHLs is also induced by and degrades the fungal lactone mycotoxin, patulin. This work supports the potential use of bacterial enzymes and/or the producing bacteria in controlling the post-harvest fruit disease caused by the patulin-producing fungus Penicillium expansum.

Composite Coating of Oleaster Gum Containing Cuminal Keeps Postharvest Quality of Cherry Tomatoes by Reducing Respiration and Potentiating Antioxidant System.

Exploring the green and affordable protection of perishable cherry tomato fruits during storage, herein, the protective efficacy, and its underpinning mechanisms, of a coating of oleaster gum, alone or incorporated with cuminal, on cherry tomatoes stored at ambient temperature was investigated. The composite coating of oleaster gum with 0.1% cuminal reduced the decay, respiration rate, weight loss, and softening of the fruits and decelerated the decreases in their total soluble solid, titratable acidity, and soluble protein levels, and therefore maintained their marketability. Furthermore, it reduced the accumulation of O2·- and H2O2 in the fruits and mitigated cell membrane lipid oxidation and permeabilization, thereby retarding their senescence. Instrumentally, it elevated the activities of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase and the levels of ascorbic acid and glutathione. This potentiation of the fruits' antioxidant system makes this composite coating a promising approach to keeping the postharvest quality of perishable fruits.

MYB24, MYB144, and MYB168 positively regulate suberin biosynthesis at potato tuber wounds during healing.

The essence of wound healing is the accumulation of suberin at wounds, which is formed by suberin polyphenolic (SPP) and suberin polyaliphatic (SPA). The biosynthesis of SPP and SPA monomers is catalyzed by several enzyme classes related to phenylpropanoid metabolism and fatty acid metabolism, respectively. However, how suberin biosynthesis is regulated at the transcriptional level during potato (Solanum tuberosum) tuber wound healing remains largely unknown. Here, 6 target genes and 15 transcription factors related to suberin biosynthesis in tuber wound healing were identified by RNA-seq technology and qRT-PCR. Dual luciferase and yeast one-hybrid assays showed that StMYB168 activated the target genes StPAL, StOMT, and St4CL in phenylpropanoid metabolism. Meanwhile, StMYB24 and StMYB144 activated the target genes StLTP, StLACS, and StCYP in fatty acid metabolism, and StFHT involved in the assembly of SPP and SPA domains in both native and wound periderms. More importantly, virus-induced gene silencing in S. tuberosum and transient overexpression in Nicotiana benthamiana assays confirmed that StMYB168 regulates the biosynthesis of free phenolic acids, such as ferulic acid. Furthermore, StMYB24/144 regulated the accumulation of suberin monomers, such as ferulates, α, ω-diacids, and ω-hydroxy acids. In conclusion, StMYB24, StMYB144, and StMYB168 have an elaborate division of labor in regulating the synthesis of suberin during tuber wound healing.

The sensor protein AaSho1 regulates infection structures differentiation, osmotic stress tolerance and virulence via MAPK module AaSte11-AaPbs2-AaHog1 in Alternaria alternata.

The high-osmolarity-sensitive protein Sho1 functions as a key membrane receptor in phytopathogenic fungi, which can sense and respond to external stimuli or stresses, and synergistically regulate diverse fungal biological processes through cellular signaling pathways. In this study, we investigated the biological functions of AaSho1 in Alternaria alternata, the causal agent of pear black spot. Targeted gene deletion revealed that AaSho1 is essential for infection structure differentiation, response to external stresses and synthesis of secondary metabolites. Compared to the wild-type (WT), the ∆AaSho1 mutant strain showed no significant difference in colony growth, morphology, conidial production and biomass accumulation. However, the mutant strain exhibited significantly reduced levels of melanin production, cellulase (CL) and ploygalacturonase (PG) activities, virulence, resistance to various exogenous stresses. Moreover, the appressorium and infection hyphae formation rates of the ∆AaSho1 mutant strain were significantly inhibited. RNA-Seq results showed that there were four branches including pheromone, cell wall stress, high osmolarity and starvation in the Mitogen-activated Protein Kinase (MAPK) cascade pathway. Furthermore, yeast two-hybrid experiments showed that AaSho1 activates the MAPK pathway via AaSte11-AaPbs2-AaHog1. These results suggest that AaSho1 of A. alternata is essential for fungal development, pathogenesis and osmotic stress response by activating the MAPK cascade pathway via Sho1-Ste11-Pbs2-Hog1.

ROS mediated by TrPLD3 of Trichothecium roseum participated cell membrane integrity of apple fruit by influencing phosphatidic acid metabolism.

Trichothecium roseum is a typical necrotrophic fungal pathogen that not only bring about postharvest disease, but contribute to trichothecenes contamination in fruit and vegetables. Phospholipase D (PLD), as an important membrane lipid degrading enzyme, can produce phosphatidic acid (PA) by hydrolyzing phosphatidylcholine (PC) and phosphatidylinositol (PI). PA can promote the production of reactive oxygen species (ROS) by activating the activity of NADPH oxidase (NOX), thereby increasing the pathogenicity to fruit. However, the ROS mediated by TrPLD3 how to influence T. roseum infection to fruit by modulating phosphatidic acid metabolism, which has not been reported. In this study, the knockout mutant and complement strain of TrPLD3 were constructed through homologous recombination, TrPLD3 was tested for its effect on the colony growth and pathogenicity of T. roseum. The experimental results showed that the knockout of TrPLD3 inhibited the colony growth of T. roseum, altered the mycelial morphology, completely inhibited the sporulation, and reduced the accumulation of T-2 toxin. Moreover, the knockout of TrPLD3 significantly decreased pathogenicity of T. roseum on apple fruit. Compared to inoculated apple fruit with the wide type (WT), the production of ROS in apple infected with ΔTrPLD3 was slowed down, the relative expression and enzymatic activity of NOX, and PA content decreased, and the enzymatic activity and gene expression of superoxide dismutase (SOD) increased. In addition, PLD, lipoxygenase (LOX) and lipase activities were considerably decreased in apple fruit infected with ΔTrPLD3, the changes of membrane lipid components were slowed down, the decrease of unsaturated fatty acid content was alleviated, and the accumulation of saturated fatty acid content was reduced, thereby maintaining the cell membrane integrity of the inoculated apple fruit. We speculated that the decreased PA accumulation in ΔTrPLD3-inoculated apple fruit further weakened the interaction between PA and NOX on fruit, resulting in the reduction of ROS accumulation of fruits, which decreased the damage to the cell membrane and maintained the cell membrane integrity, thus reducing the pathogenicity to apple. Therefore, TrPLD3-mediated ROS plays a critical regulatory role in reducing the pathogenicity of T. roseum on apple fruit by influencing phosphatidic acid metabolism.

The small GTPase Ypt7 of Penicillium expansum is required for growth, patulin biosynthesis and virulence.

Ypt GTPases are the largest subfamily of small GTPases involved in membrane transport. Here, a PeYpt7 gene deletion mutant of P. expansum was constructed. The ΔPeYpt7 mutant showed reduced colony growth with abnormal mycelial growth, reduced conidiation, and insufficient spore development. The mutation rendered the pathogen susceptible to osmotic stress and cell wall stressors. In addition, the absence of PeYpt7 reduced patulin production in P. expansum and significantly limited gene expression (PatG, PatH, PatI, PatD, PatF, and PatL). In addition, the mutant showed attenuated virulence in infected fruit and reduced expression of pathogenic factors was (PMG, PG, PL, and GH1). Thus, PeYpt7 modulates the growth, morphology, patulin accumulation, and pathogenicity of P. expansum by limiting the expression of related genes.

The histone demethylase KdmB is part of a trimeric protein complex and mediates virulence and mycotoxin production in Penicillium expansum.

Epigenetic modification of chromosome structure has increasingly been associated with alterations in secondary metabolism and sporulation defects in filamentous fungal pathogens. Recently, the epigenetic reader protein SntB was shown to govern virulence, spore production and mycotoxin synthesis in the fruit pathogen Penicillium expansum. Through immunoprecipitation-coupled mass spectrometry, we found that SntB is a member of a protein complex with KdmB, a histone demethylase and the essential protein RpdA, a histone deacetylase. Deletion of kdmB phenocopied some but not all characteristics of the ΔsntB mutant. KdmB deletion strains exhibited reduced lesion development on Golden Delicious apples and this was accompanied by decreased production of patulin and citrinin in host tissue. In addition, ΔkdmB mutants were sensitive to several cell wall stressors which possibly contributed to the decreased virulence observed on apples. Slight differences in spore production and germination rates of ΔkdmB mutants in vitro did not impact overall diameter growth in culture.

Erg4 Is Involved in Ergosterol Biosynthesis, Conidiation and Stress Response in Penicillium expansum.

erg4 is a key gene for ergosterol biosynthesis in filamentous fungi, but its function in Penicillium expansum remains unknown. Our results showed that P. expansum contains three erg4 genes, including erg4A, erg4B and erg4C. The expression levels of the three genes showed differences in the wild-type (WT) strain, and the expression level of erg4B was the highest, followed by erg4C. Deletion of erg4A, erg4B or erg4C in the WT strain revealed functional redundancy between them. Compared to the WT strain, erg4A, erg4B or erg4C knockout mutants reduced ergosterol levels, with erg4B deletion having the greatest effect. Furthermore, deletion of the three genes reduced sporulation of the strain, and Δerg4B and Δerg4C mutants showed defective spore morphology. In addition, Δerg4B and Δerg4C mutants were found to be more sensitive to cell wall integrity and oxidative stress. However, deletion of erg4A, erg4B or erg4C had no significant effect on colony diameter, spore germination rate, conidiophore structure of P. expansum or pathogenicity to apple fruit. Taken together, erg4A, erg4B and erg4C have redundant functions and are all involved in ergosterol synthesis and sporulation in P. expansum. In addition, erg4B and erg4C contribute to spore morphogenesis, cell wall integrity and response to oxidative stress in P. expansum.

Induced Resistance in Fruit and Vegetables: A Host Physiological Response Limiting Postharvest Disease Development.

Harvested fruit and vegetables are perishable, subject to desiccation, show increased respiration during ripening, and are colonized by postharvest fungal pathogens. Induced resistance is a strategy to control diseases by eliciting biochemical processes in fruits and vegetables. This is accomplished by modulating the progress of ripening and senescence, which maintains the produce in a state of heightened resistance to decay-causing fungi. Utilization of induced resistance to protect produce has been improved by scientific tools that better characterize physiological changes in plants. Induced resistance slows the decline of innate immunity after harvest and increases the production of defensive responses that directly inhibit plant pathogens. This increase in defense response in fruits and vegetables contributes to higher amounts of phenols and antioxidant compounds, improving both the quality and appearance of the produce. This review summarizes mechanisms and treatments that induce resistance in harvested fruits and vegetables to suppress fungal colonization. Moreover, it highlights the importance of host maturity and stage of ripening as limiting conditions for the improved expression of induced-resistance processes.

Chitosan and chitooligosaccharide regulated reactive oxygen species homeostasis at wounds of pear fruit during healing.

Both chitosan (CTS) and chitooligosaccharide (COS) can promote fruit healing. However, whether the two chemicals regulate reactive oxygen species (ROS) homeostasis during wound healing of pear fruit remains unknown. In this study, the wounded pear fruit (Pyrus bretschneideri cv. Dongguo) was treated with a 1 g L-1 CTS and COS. We found CTS and COS treatments increased NADPH oxidase and superoxide dismutase activities, and promoted O2.- and H2O2 production at wounds. CTS and COS also enhanced the activities of catalase, peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, and elevated the levels of ascorbic acid and glutathione. In addition, the two chemicals improved antioxidant capacity in vitro and maintained cell membrane integrity at fruit wounds during healing. Taken together, CTS and COS can regulate ROS homeostasis at wounds of pear fruit during healing by scavenging excessive H2O2 and improving antioxidant capacity. Overall, the COS demonstrated superior performance over the CTS.

Chitooligosaccharide accelerated wound healing in potato tubers by promoting the deposition of suberin polyphenols and lignin at wounds.

Chitooligosaccharide (COS) is a low molecular weight product of chitosan degradation. Although COS induces plant resistance by activating phenylpropanoid metabolism, there are few reports on whether COS accelerates wound healing in potato tubers by promoting the deposition of phenolic acids and lignin monomers at wounds. The results showed that COS activated phenylalanine ammonialyase and cinnamate 4-hydroxylase and promoted the synthesis of cinnamic, caffeic, p-coumaric, ferulic acids, total phenolics and flavonoids. COS activated 4-coumaric acid coenzyme A ligase and cinnamyl alcohol dehydrogenase and promoted the synthesis of sinapyl, coniferyl and cinnamyl alcohols. COS also increased H2O2 levels and peroxidase activity and accelerated the deposition of suberin polyphenols and lignin on wounds. In addition, COS reduced weight loss and inhibited lesion expansion in tubers inoculated with Fusarium sulfureum. Taken together, COS accelerated wound healing in potato tubers by inducing phenylpropanoid metabolism and accelerating the deposition of suberin polyphenols and lignin at wounds.

Sodium silicate treatment accelerates biosynthesis and polymerization of suberin polyaliphatics monomers at wounds of muskmelon.

Suberin polyaliphatics (SPA) is an important component of healing closing layer at fruit wounds. However, few study is available on the effect of sodium silicon treatment on SPA monomers biosynthesis and polymerization at muskmelon wounds. In this study, sodium silicate enhanced PLA2 (Phospholipase A2, PLA2) expression and enzyme activity, increased oleic acid, linoleic acid, and linolenic acid contents, and degree of fatty acids unsaturation at wounds. Sodium silicate upregulated the expressions of LACS4 (Long chain acyl CoA synthetase, LACS), KCS10 (ß-ketoacyl CoA synthase, KCS), CYP86B1 (Cytochrome P450 oxygenase, CYP), FAR3 (Fatty acyl CoA reductase, FAR), GPAT1 (Glycerol-3-phosphate acyltransferase, GPAT) and ABCG6 (ATP-binding cassette transporter), as well as their enzymes activities and ABC content. It is suggested that sodium silicate accelerates the deposition of SPA at muskmelon wounds by increasing the degree of fatty acids unsaturation, and promoting SPA monomers biosynthesis.

Mechanical wounds expedited starch degradation in the wound tissues of potato tubers.

Starch degradation occurs rapidly in stressed plants, but it is unclear how starch degradation occurs in potato tubers after they incur mechanical wounding. In this study, we found that wounding significantly upregulated the expression levels of StGWD, StAMY, StBAM, and StISA, and decreased the starch content of potato tubers. Meanwhile, wounding markedly upregulated the expression levels of StSUS, StBG, and StINV genes, and increased the content of sucrose, glucose, and fructose. Furthermore, wounding reduced the proportion of small starch granules and increase that of large as well as medium starch granules, in this way enhancing the average size distribution of starch. Initially, the hard surface layer of starch granules was removed by wounding, but the internal channels and other structures were only slightly affected. Taken together, the results show that wounding can accelerate starch degradation by promoting the accumulation of sucrose, glucose, and fructose, and the hydrolysis of starch granules in potato tubers.

Meyerozyma guilliermondii promoted the deposition of GSH type lignin by activating the biosynthesis and polymerization of monolignols at the wounds of potato tubers.

Lignin is a crucial component in the wound tissue of tubers. The biocontrol yeast Meyerozyma guilliermondii increased the activities of phenylalanine ammonia lyase, cinnamate-4-hydroxylase, 4-coenzyme coenzyme A ligase, and cinnamyl alcohol dehydrogenase, and elevated the levels of coniferyl, sinapyl, and p-coumaryl alcohol. The yeast also enhanced the activities of peroxidase and laccase, as well as the content of hydrogen peroxide. The lignin promoted by the yeast was identified as guaiacyl-syringyl-p-hydroxyphenyl type using Fourier transform infrared spectroscopy and two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance. Furthermore, a larger signal area for G2, G5, G'6, S2, 6, and S'2, 6 units was observed in the treated tubers, and the G'2 and G6 units were only detected in the treated tuber. Taken together, M. guilliermondii could promote deposition of guaiacyl-syringyl-p-hydroxyphenyl type lignin by activating the biosynthesis and polymerization of monolignols at the wounds of potato tubers.

BTH-induced joint regulation of wound healing at the wounds of apple fruit by JA and its downstream transcription factors.

Jasmonic acids (JAs) are important injury signaling molecules, which participate in the process of wound healing in plants. However, how JA and its downstream transcription factors involve in wound healing in apple fruit mediated by BTH has not been reported yet. In the present study, BTH treatment up-regulated gene expression of MdLOX3.1, MdAOS1, MdAOC, and MdOPR3, promoting JA synthesis at fruit wounds. Moreover, BTH up-regulated the gene expression of MdMYC2, MdGAIPB, and MdMYB108 transcription factors and increased MdPAL1, Md4CL2, MdCOMT1, and MdCAD6 expression. In addition, BTH facilitated the synthesis of phenylpropanoid metabolism products and accelerated suberin polyphenolics deposition at the wounds, which effectively reduced fruit weight loss and lesion diameter of apple fruit inoculated with Penicillium expansum during healing. It is suggested that BTH induced wound healing in apple fruit by the stimulating JA and its downstream transcription factors, and phenylpropanoid metabolism.