Pyrus Bretschneideri Rehd Research Articles

Integration of mRNA-miRNA Reveals the Possible Role of PyCYCD3 in Increasing Branches Through Bud-Notching in Pear (Pyrus bretschneideri Rehd.).

Bud-notching in pear varieties with weak-branches enhances branch development, hormone distribution, and germination, promoting healthier growth and improving early yield. To examine the regulatory mechanisms of endogenous hormones on lateral bud germination in Pyrus spp. (cv. 'Huangguan') (Pyrus bretschneideri Rehd.), juvenile buds were collected from 2-year-old pear trees. Then, a comprehensive study, including assessments of endogenous hormones, germination and branching rates, RNA-seq analysis, and gene function analysis in these lateral buds was conducted. The results showed that there was no significant difference in germination rate between the control and bud-notching pear trees, but the long branch rate was significantly increased in bud-notching pear trees compared to the control (p < 0.05). After bud-notching, there was a remarkable increase in IAA and BR levels in the pruned section of shoots, specifically by 141% and 93%, respectively. However, the content of ABA in the lateral buds after bud-notching was not significantly different from the control. Based on RNA-seq analysis, a notable proportion of the differentially expressed genes (DEGs) were linked to the plant hormone signal transduction pathway. Notably, the brassinosteroid signaling pathway seemed to have the closest connection with the branching ability of pear with the related genes encoding BRI1 and CYCD3, which showed significant differences between lateral buds. Finally, the heterologous expression of PyCYCD3 has a positive regulatory effect on the increased Arabidopsis growth and branching numbers. Therefore, the PyCYCD3 was identified as an up-regulated gene that is induced via brassinosteroid (BR) and could act as a conduit, transforming bud-notching cues into proliferative signals, thereby governing lateral branching mechanisms in pear trees.

6-Methyl-5-hepten-2-one promotes programmed cell death during superficial scald development in pear

Plants possess the ability to induce programmed cell death (PCD) in response to abiotic and biotic stresses; nevertheless, the evidence on PCD initiation during pear scald development and the involvement of the scald trigger 6-methyl-5-hepten-2-one (MHO) in this process is rudimentary. Pyrus bretschneideri Rehd. cv. ‘Dangshansuli’ pear was used to validate such hypothesis. The results showed that superficial scald occurred after 120-d chilling exposure, which accompanied by typical PCD-associated morphological alterations, such as plasmolysis, cell shrinkage, cytosolic and nuclear condensation, vacuolar collapse, tonoplast disruption, subcellular organelle swelling, and DNA fragmentation. These symptoms were aggravated after MHO fumigation but alleviated by diphenylamine (DPA) dipping. Through transcriptome assay, 24 out of 146 PCD-related genes, which were transcribed during cold storage, were identified as the key candidate members responsible for these cellular biological alternations upon scald development. Among these, PbrCNGC1, PbrGnai1, PbrACD6, and PbrSOBIR1 were implicated in the MHO signaling pathway. Additionally, PbrWRKY2, 34 and 39 could bind to the W-box element in the promoter of PbrGnai1 or PbrSOBIR1 and activate their transcription, as confirmed by dual-luciferase, yeast one-hybrid, and transient overexpression assays. Hence, our study confirms the PCD initiation during scald development and explores the critical role of MHO in this process.

Variation in Bacterial and Fungal Communities in Soils from Three Major Apple Pear (Pyrus bretschneideri Rehd.) Orchards.

Microbial communities are closely related to the overall health and quality of soil, but studies on microbial ecology in apple pear orchard soils are limited. In the current study, 28 soil samples were collected from three apple pear orchards, and the composition and structure of fungal and bacterial communities were investigated by high-throughput sequencing. The molecular ecological network showed that the keystone taxa of bacterial communities were Actinobacteria, Proteobacteria, Gemmatimonadetes, Acidobacteria, Nitrospirae, and Chloroflexi, and the keystone taxon of fungal communities was Ascomycota. Mantel tests showed that soil texture and pH were important factors shaping soil bacterial and fungal communities, and soil water soluble organic carbon (WSOC) and nitrate nitrogen (NO3--N) were also closely related to soil bacterial communities. Canonical correspondence analysis (CCA) and variation partition analysis (VPA) revealed that geographic distance, soil texture, pH, and other soil properties could explain 10.55%, 13.5%, and 19.03% of the overall variation in bacterial communities, and 11.61%, 13.03%, and 20.26% of the overall variation in fungal communities, respectively. The keystone taxa of bacterial and fungal communities in apple pear orchard soils and their strong correlation with soil properties could provide useful clues toward sustainable management of orchards.

Chloroplast Genome Profiling and Phylogenetic Insights of the “Qixiadaxiangshui” Pear (Pyrus bretschneideri Rehd.1)

The “Qixiadaxiangshui” pear (Pyrus bretschneideri Rehd.1) is a highly valued cultivar known for its crisp texture, abundant juice, and rich aroma. In this study, we reported the first complete chloroplast genome sequence of the “Qixiadaxiangshui” pear, which is 159,885 bp in length with a GC content of 36.58%. The genome exhibits a typical circular quadripartite structure, comprising a large single-copy region (LSC), a small single-copy region (SSC), and a pair of inverted repeat regions (IRs). A total of 131 genes were identified, including 84 protein-coding genes, 8 rRNA genes, and 37 tRNA genes. We also identified 209 simple sequence repeats (SSRs) and several mutation hotspots, such as ndhC-trnM-CAU and trnR-UCU-atpA, which can be applied in molecular identification and phylogenetic studies of Pyrus. Comparative genomic analysis showed high conservation among ten pear cultivars. Phylogenetic analysis indicated that the “Qixiadaxiangshui” pear is closely related to germplasm Dangshansuli, Wonwhang, and Yali, suggesting a recent common ancestor. These findings provided valuable insights into the genetic diversity and evolutionary dynamics of the Pyrus species and contribute to the conservation and breeding of pear germplasm resources.

The Fungal Diversity and Potential Pathogens Associated with Postharvest Fruit Rot of 'Huangguan' Pear (Pyrus bretschneideri) in Hebei Province, China.

Postharvest fruit rot caused by pathogens is a serious problem in the pear industry. This study investigated the fungal diversity and main pathogens and identified a new pathogen in the stored 'Huangguan' pear (Pyrus bretschneideri Rehd.), the dominant pear variety in northern China. We sampled 20 refrigeration houses from five main producing regions in Hebei Province and used Illumina sequencing technology to detect the fungal composition. Alternaria (56.3%) was the most abundant fungus, followed by Penicillium (9.2%) and Monilinia (6.2%). We also isolated and identified nine strains of Alternaria and four strains of Penicillium. Moreover, we observed a new postharvest fruit disease in 'Huangguan' pear caused by Stemphylium eturmiunum, which was confirmed by phylogenetic analysis by combining the sequences of three conserved genes, including internal transcribed spacer, gapdh, and calmodulin. This study marks the first documentation of S. eturmiunum causing fruit rot in 'Huangguan' pears, offering valuable insights for identifying and controlling this newly identified postharvest disease.

Reactive Oxygen Species and Salicylic Acid Mediate the Responses of Pear to Venturia nashicola Infection

Reactive oxygen species (ROS) and salicylic acid (SA) are essential signaling molecules in plant cells that participate in responses to biotic and abiotic stresses. Changes in ROS and SA signals during interactions between pear and the pear scab pathogen Venturia nashicola remain unclear. Herein, we analyzed the roles of ROS in the signal transduction pathway of pear scab resistance using the highly resistant Huangguan and susceptible Xuehua cultivars of pear (Pyrus bretschneideri Rehd). Protoplasts, calluses, and leaves were obtained from 14-year-old pear trees and treated with V. nashicola for different periods. The results showed that ROS rapidly accumulated in protoplasts of both cultivars within a 120-min treatment period, but the fluorescence intensity of ROS differed between cultivars. The H2O2 content in fruit-derived calluses of Huangguan peaked at 48 h post-infection at levels 1.85 times higher than those in Xuehua. Induction of H2O2 by V. nashicola in Huangguan was more intense than in Xuehua over a 96-h treatment period. At 96 h post-infection, the malondialdehyde content in leaves of Huangguan was significantly lower than in Xuehua, while the activities of superoxide dismutase, peroxidase, and catalase, and the relative expression levels of PbMnSOD, PbPOD, and PbCAT genes were higher in Huangguan than Xuehua. V. nashicola infection also caused a continuous increase in the leaf SA content of Huangguan, which was 6.76 times higher than in Xuehua at 96 h post-infection, and V. nashicola exposure upregulated the expression of PbPAL, PbICS, PbPR1, and PbPR5. In summary, both ROS and SA participated in the responses of pear trees to V. nashicola infection and played vital roles in the signal transduction pathway of pear scab resistance.

Preservative effects of Osmanthus fragrans flower flavonoids on fresh-cut Yuluxiang pear

Osmanthus fragrans flower flavonoids (OFFF) possess superior antioxidant and antibacterial activities. However, scant information exists on the efficacy of these secondary metabolites as preservatives for fresh-cut fruits and vegetables. Here, OFFF were tested as a natural preservative for the first time in fresh-cut Yuluxiang pear (Pyrus bretschneideri Rehd.) to assess effects on fruit quality. OFFF-treated samples showed significant retention of firmness, titratable acid, soluble solid content, and weight. Moreover, OFFF maintained the original fruit color, inhibited the decline of total phenol, reducing power and 2,2-diphenyl-1-picrylhydrazyl radical scavenging power, and diminished polyphenol oxidase and peroxidase oxidase activities. Furthermore, OFFF treatment effectively inhibited microbial growth. OFFF-treated samples also displayed better sensory quality. Considering cost and effectiveness, the most suitable concentrations of OFFF extract for fresh-cut Yuluxiang pear preservation were 0.7 and 0.9 mg/mL. The results indicate that OFFF treatment may be a potent strategy to inhibit browning and enhance nutritional properties of fresh-cut pear fruit.

Deciphering the Virome of the Pimple-Shaped ‘Yali’ Pear Fruit through High-Throughput Sequencing

Viral diseases pose a threat to fruit tree growth. In this study, we observed some pimple-shaped ‘Yali’ pears (Pyrus bretschneideri Rehd.) and investigated their viral components. We used virome analysis to elucidate the viral composition within the pimple-shaped fruit. RT-PCR was applied to detect the plant viruses of fruits, leaves, and branches in ‘Yali’ pear. We also constructed a phylogenetic tree based on the amino acid sequences of the movement proteins of 6 apple stem grooving virus (ASGV) isolates and 44 ASGVs from the NCBI database. We detected ASGV and apple stem pitting virus (ASPV) in the pimple-shaped pear fruits, which is the first report of these viruses existing in ‘Yali’ pear fruits. ASGV was present in all pimple-shaped fruit samples from six ‘Yali’ pear-producing regions. The phylogenetic tree showed that ASGVs from pears, apples, and citrus plants were separated into different branches, suggesting that hosts influence the genetic diversity of ASGV. Our study revealed the viral components and genetic variation of ASGV in pimple-shaped pear fruit, providing new insights into the epidemiology of this virus.

PbBPC4 involved in a xylem-deficient dwarf phenotype in pear by directly regulating the expression of PbXND1

Dwarfing is an important agronomic trait in fruit breeding. At present, dwarf cultivars or dwarfing rootstocks are used for high-density planting. Although some dwarf rootstocks have been used in the cultivation of pear (Pyrus bretschneideri Rehd), the breeding of dwarf pear rootstocks or cultivars is still sorely lacking. A previous study reported that PbXND1 results in a xylem-dwarf phenotype in pear trees. However, the regulatory mechanism upstream of PbXND1 is unclear. In this study, we identified PbBPC4 as an upstream regulatory factor of PbXND1 in yeast one-hybrid assays. In β-glucuronidase staining and dual-luciferase assays, PbBPC4 enhanced the activity of the PbXND1 promoter. Tobacco plants overexpressing PbBPC4 showed decreased plant height because of a reduced xylem size. Similar changes in the xylem was observed in transgenic pear roots; those overexpressing PbBPC4 showed reduced xylem size, and those with silencing PbBPC4 expression showed increased xylem size, greater density of xylem vessels, and a larger proportion of the xylem out of the total cross-section area. Expression analyses showed that PbBPC4 increases the transcription of PbXND1, leading to reduced transcript levels of genes involved in the positive regulation of xylem development, ultimately resulting in a xylem-deficient dwarf phenotype. Taken together, our results reveal the mechanism by which PbBPC4 participates in the regulation of xylem development via directly altering the expression of PbXND1, thus leading to the dwarf phenotype in pear. These findings have reference value for the breeding of dwarf pear trees.

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

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

Evidence That PbrSAUR72 Contributes to Iron Deficiency Tolerance in Pears by Facilitating Iron Absorption.

Iron is an essential trace element for plants; however, low bioactive Fe in soil continuously places plants in an Fe-deficient environment, triggering oxidative damage. To cope with this, plants make a series of alterations to increase Fe acquisition; however, this regulatory network needs further investigation. In this study, we found notably decreased indoleacetic acid (IAA) content in chlorotic pear (Pyrus bretschneideri Rehd.) leaves caused by Fe deficiency. Furthermore, IAA treatment slightly induced regreening by increasing chlorophyll synthesis and Fe2+ accumulation. At that point, we identified PbrSAUR72 as a key negative effector output of auxin signaling and established its close relationship to Fe deficiency. Furthermore, the transient PbrSAUR72 overexpression could form regreening spots with increased IAA and Fe2+ content in chlorotic pear leaves, whereas its transient silencing does the opposite in normal pear leaves. In addition, cytoplasm-localized PbrSAUR72 exhibits root expression preferences and displays high homology to AtSAUR40/72. This promotes salt tolerance in plants, indicating a putative role for PbrSAUR72 in abiotic stress responses. Indeed, transgenic plants of Solanum lycopersicum and Arabidopsis thaliana overexpressing PbrSAUR72 displayed less sensitivity to Fe deficiency, accompanied by substantially elevated expression of Fe-induced genes, such as FER/FIT, HA, and bHLH39/100. These result in higher ferric chelate reductase and root pH acidification activities, thereby hastening Fe absorption in transgenic plants under an Fe-deficient condition. Moreover, the ectopic overexpression of PbrSAUR72 inhibited reactive oxygen species production in response to Fe deficiency. These findings contribute to a new understanding of PbrSAURs and its involvement in Fe deficiency, providing new insights for the further study of the regulatory mechanisms underlying the Fe deficiency response.

Genome-wide identification and characterization of the PbrATG family in Pyrus bretschneideri and functional analysis of PbrATG1a in response to Botryosphaeria dothidea

The pear is an economic fruit that is widely planted around the world and is loved by people for its rich nutritional value. Autophagy is a self-protection mechanism in eukaryotes, and its occurrence often accompanied by the degradation of damaged substances in cells and the recycling of nutrients. Autophagy is one of the mechanisms through which plants respond to environmental stress and plays an important role in plant development and stress resistance. Functional studies of autophagy-related genes (ATGs) have been performed on a variety of plant species, but little information is available on the ATG family in pear (Pyrus bretschneideri Rehd). Therefore, we analyzed the evolutionary dynamics and performed a genome-wide characterization of the PbrATG gene family. A total of 28 PbrATG members were identified. Phylogenetic analysis showed that PbrATGs were more closely related to ATGs of European pear and apple. Evolutionary analysis revealed that whole-genome duplication (WGD) and dispersed duplication events were the main driving forces of PbrATG family expansion. Expression analysis of different pear tissues showed that all the genes were expressed in different pear tissues, and different PbrATGs are expressed at different times and in different locations. Moreover, all PbrATGs also responded to different abiotic stresses, especially salt and drought stress, which elicited the highest expression levels. Pear seedlings were subsequently infected with Botryosphaeria dothidea (B. dothidea). The results showed that different PbrATGs had different expression patterns at different infection stages. According to the gene expression data, PbrATG1a was selected as a key autophagy gene for further analysis. Silencing of PbrATG1a reduced the resistance of pear to B. dothidea, which resulted in increased lesions, reactive oxygen species (ROS) contents, antioxidant enzyme activity, and gene expression levels in the silenced pear seedlings after B. dothidea inoculation. In this study, a comprehensive bioinformatic analysis of ATGs was conducted, and the functions of PbrATGs in pear development and in response to stress were elucidated, which laid a foundation for further study of the molecular mechanism of autophagy and a new strategy for pear resistance breeding.

Effects of different vibration spectrum shapes on mechanical damage of postharvest Huangguan pear during transportation

Mechanical damage of the horticultural produce during postharvest transportation is an important criteria for fruit sorting and grading. The vibration during transportation has a significant effect on the mechanical damage of the fruit. In this study, the effect of different vibration spectrum shapes on mechanical damage of Huangguan pear (Pyrus bretschneideri Rehd, cv. Huangguan) was investigated. Four acceleration spectrums (spectrum Ⅰ, spectrum Ⅱ, spectrum Ⅲ, and spectrum Ⅳ) with same vibration level and different shapes were evaluated. The power spectral density (PSD) amplitude in the resonant region was in the order of spectrum Ⅰ > spectrum Ⅱ> spectrum Ⅲ > spectrum Ⅳ. The change in appearance, physiological properties (respiratory rate and weight loss), and mechanical properties (firmness and elastic modulus) of the pears were evaluated after vibration. Results showed that vibration resulted in quality deterioration of pear. Compared to the control group, respiratory rate and weight loss of the pears increased while the flesh firmness and elastic modulus of the pears decreased after vibration. The mechanical damage became more serious as stacked position increased. The effect of spectrum shape on the mechanical damage of pear was also obvious. Different degree of mechanical damage was observed under spectrum Ⅰ, spectrum Ⅱ, spectrum Ⅲ, and spectrum Ⅳ vibration. The higher the acceleration PSD in resonant region, the more serious the mechanical damage of pear. In comparison with the control group, pear under spectrum Ⅰ effect showed the most mechanical damage and the pear under spectrum Ⅳ effect had the minimum mechanical damage. Furthermore, S−Grms curves (damage area - vibration level) showed a clockwise rotation from spectrum Ⅰ to Ⅲ vibration. This study reveals the mechanical damage mechanism of pears based on acceleration spectrum shape and provides guidance for postharvest loss reduction using simulated test.

Alternaria alternata stimulates blackhead disease development of ‘Korla’ fragrant pear (Pyrus bretschneideri Rehd) by regulating energy status and respiratory metabolism

Blackhead disease of ‘Korla’ fragrant pear (Pyrus bretschneideri Rehd), caused by the fungus Alternaria alternata (A. alternata), limits postharvest pear fruit storage and transportation. Herein, we explored the effects of A. alternata infection on respiratory metabolism and energy status of pear fruit, and their correlations with disease development. Compared with control fruit, A. alternata-inoculated fruit displayed a higher respiration rate and disease index. Infection increased the gene expression and enzyme activities of phosphohexose isomerase (PGI), alternative oxidase (AOX), succinate dehydrogenase (SDH) and cytochrome C oxidase (CCO) in pear fruit, and decreased those of 6-phosphogluconate dehydrogenase (6PGDH) and glucose-6-phosphate dehydrogenase (G6PDH) in the late storage period. Infection reduced nicotinamide adenine dinucleotide kinase (NADK) activity and expression level in fruit, inhibited NADP accumulation, and increased NAD, NADH, and NADPH contents in the early storage period. Infection also lowered adenosine triphosphate (ATP), adenosine diphosphate (ADP) and energy charge (EC) levels as well as ATPase activity, and enhanced adenosine monophosphate (AMP) content and PbAtpB expression levels, resulting in decreased fruit energy status. All these results suggest that disease development may be connected to the enhancement of the Embden-Meyerhof-Parnas (EMP) pathway, the tricarboxylic acid (TCA) cycle, the cytochrome pathway (CCP), the alternative pathway (AP), the increased then decrease in the pentose phosphate pathway (PPP), and reduced energy status in pear fruit.

Genome-Wide Identification and Expression Analysis of the fw2.2-like Gene Family in Pear

Fruit size is a major factor determining yield, quality, and consumer acceptability. fw2.2 (fruit weight-2.2) is a primary quantitative trait locus that was the first to be cloned, accounting for 30% of the variation in tomato fruit size. The various homologs of fw2.2 (fw2.2-like) have been identified in many plants and belong to a large family. To date, there has been no report that has carried out a comprehensive identification of fw2.2-like members in pear. In this study, a total of 14 fw2.2-like genes were identified in the pear (Pyrus bretschneideri Rehd) genome and designated as PbFWL1-14. All of the PbFWL genes were unevenly distributed on nine chromosomes, and each chromosome contained between one and four genes. All PbFWL proteins contained more than two conserved motifs, and PbFWL genes contained more than one intron, and the genes of the same subfamily seemed to have a similar intron gene structure. According to the neighbor-joining phylogenetic tree, a total of 78 fw2.2/CNR (cell number regulator) from five plant species, including pear, maize, tomato, peach, rice, and physalis, could be divided into seven subgroups, and PbFWL proteins were mainly distributed in subgroups 1, 3, 4, 5, and 6. The Ka/Ks analysis also revealed that the fw2.2-like gene family of pear may have been subjected to strong purifying selection pressure during its evolution. A cis-element analysis found that many cis-elements responsive to hormones and stress were discovered in promotion regions for all PbFWLs. When combining real-time quantitative PCR analysis detection results, PbFWL1/2/5 were found to be the most likely candidate genes for regulating pear fruit size.

Changes of Bioactive Components and Antioxidant Capacity of Pear Ferment in Simulated Gastrointestinal Digestion In Vitro.

Fruit ferment is rich in polyphenols, organic acids, enzymes, and other bioactive components, which contribute to their antioxidant ability. In this study, we investigated the effect of the simulated gastric and intestinal digestion in vitro on the total phenolic content (TPC), total flavonoid content (TFC), phenolic components content, organic acid content, protease activity, superoxide dismutase (SOD) activity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (DPPH-RSA), hydroxyl (·OH) radical scavenging activity (·OH-RSA), and total reducing capacity in 'Xuehua' pear (Pyrus bretschneideri Rehd) ferment. The result showed that the TPC, TFC, protease activity, and phenolic components such as arbutin, protocatechuic acid, malic acid, and acetic acid showed a rising trend during the simulated gastric digestion in 'Xuehua' pear ferment, and these components might contribute to the increasing of ·OH-RSA and total reducing capacity. The SOD activity and epicatechin content showed an increasing trend at first and then a decreasing trend, which was likely associated with DPPH-RSA. During in vitro-simulated intestinal digestion, the majority of evaluated items reduced, except for protease activity, quercetin, and tartaric acid. The reason for the decreasing of bio-accessibility resulted from the inhibition of the digestive environment, and the transformation between substances, such as the conversion of hyperoside to quercetin. The correlation analysis indicated that the antioxidant capacity of 'Xuehua' pear ferment was mainly affected by its bioactive compounds and enzymes activity as well as the food matrices and digestive environment. The comparison between the digestive group with and without enzymes suggested that the simulated gastrointestinal digestion could boost the release and delay the degradation of phenolic components, flavonoids, and organic acid, protect protease and SOD activity, and stabilize DPPH-RSA, ·OH-RSA, and total reducing capacity in 'Xuehua' pear ferment; thus, the 'Xuehua' pear ferment could be considered as an easily digestible food.

Time-Series Transcriptome Analysis Reveals the Molecular Mechanism of Ethylene Reducing Cold Sensitivity of Postharvest 'Huangguan' Pear.

'Huangguan' pear (Pyrus bretschneideri Rehd) fruit is susceptible to cold, characterized by developing peel browning spots (PBS) during cold storage. Additionally, ethylene pretreatment reduces chilling injury (CI) and inhibits PBS occurrence, but the mechanism of CI remains unclear. Here, we deciphered the dynamic transcriptional changes during the PBS occurrence with and without ethylene pretreatment via time-series transcriptome. We found that ethylene suppressed the cold-signaling gene expression, thereby decreasing the cold sensitivity of the 'Huangguan' fruit. Moreover, the "Yellow" module closely correlated with PBS occurrence was identified via weighted gene co-expression network analysis (WGCNA), and this module was related to plant defense via Gene Ontology (GO) enrichment analysis. Local motif enrichment analysis suggested that the "Yellow" module genes were regulated by ERF and WRKY transcription factors. Functional studies demonstrated that PbWRKY31 has a conserved WRKY domain, lacks transactivation activity, and localizes in the nucleus. PbWRKY31-overexpressed Arabidopsis were hypersensitive to cold, with higher expression levels of cold signaling and defense genes, suggesting that PbWRKY31 participates in regulating plant cold sensitivity. Collectively, our findings provide a comprehensive transcriptional overview of PBS occurrence and elucidate the molecular mechanism by which ethylene reduces the cold sensitivity of 'Huangguan' fruit as well as the potential role of PbWRKY31 in this process.

Modulation of gut flore by dietary fibers from Pyrus bretschneideri Rehd.: Evaluation of fermentation characteristics using a colonic in vitro fermentation model

Nutrients such as dietary fiber in Pyrus bretschneideri Rehd. (PBR), which is mainly produced on the Tibetan Plateau, can be used as a fermentable carbon source for microorganisms. However, the mechanisms by which different carbon sources interact with microorganisms and their fermentation metabolites are not clear. In this study, four different carbon sources extracted from PBR were used to explore the effect of carbon source type on gut flora (GF) and the metabolites thereof through an in vitro simulated colonic fermentation model. The results showed a differentiation of the type of carbon source on the species composition and structure of GF, as well as on the production of metabolites during in vitro fermentation. Correlations between some microbial taxa and their metabolites were also revealed, such as Subdoligranulum and acetic acid, Collinsella and propionic acid, and Fusicatenibacter and butyric acid showing significant positive correlations. Notably, a cross-feeding pathway was clarified: Anaerostipes uses lactic acid and acetic acid as substrates to produce butyric acid. Overall, this study provided insight into the effects of different carbon sources from PBR as fermentation substrates on GF growth and metabolism, which could provide a basis for exploring the relationship between carbon source types, GF and their metabolites, and promote the integrated development of PBR resources in Qinghai Province.

Effects of Preharvest Aminoethoxyvinylglycine (AVG) Treatment on Fruit Ripening, Core Browning and Related Gene Expression in ‘Huangguan’ Pear (Pyrus bretschneideri Rehd.)

‘Huangguan’ pear (Pyrus bretschneideri Rehd. cv. Huangguan) is a widely planted cultivar in China. However, it is susceptible to core browning after harvest. In this study, aminoethoxyvinylglycine (AVG) was applied at 200 mg L−1 one and two weeks prior to harvest, and its effects on fruit quality, ripening and core browning were investigated during fruit storage at ambient temperature (25 ± 1 °C). The results showed that there was higher firmness, soluble solids content (SSC) and titratable acid (TA) content, but a lower ethylene production rate and core browning index in AVG-treated fruit than in control (water). Compared with the control fruit, AVG treatment decreased the malondialdehyde (MDA) content and polyphenol oxidase (PPO) activity, delayed the peak of chlorogenic acid (CGA) content in the core tissue, and significantly inhibited the expression of genes such as ACC synthase (PbACS2, PbACS3a, PbACS5a and PbASC5b), ACC oxidase (PbACO1 and PbACO2), ethylene receptors (PbETR2 and PbERS1), ethylene response factor (PbERF1), phenylalanine ammonia lyase (PbPAL1), cinnamate 4-hydroxylase (PbC4H4), 4-hydroxycinnamoyl- CoA ligase (Pb4CL2), hydroxycinnamoyl- CoA shikimate hydroxycinnamoyl transferase (PbHCT1 and PbHCT3), and polyphenol oxidase (PbPPO1 and PbPPO5), as well as phospholipase D (PbPLD) and lipoxygenase (PbLOX1 and PbLOX5). Thus, these results suggested that the reduction in core browning by preharvest application of AVG might be due to an inhibitory effect on the expression of genes associated with ethylene biosynthesis and signaling pathways, CGA biosynthesis, PPO and cell membrane degradation in ‘Huangguan’ pear.

Integrated transcriptome and metabolome analysis unveiled the mechanisms of xenia effect and the role of different pollens on aroma formation in ‘Yali’ pear (Pyrus bretschneideri Rehd)

• ‘Hongnanguo’ pollinizer has a xenia effect on ‘Yali’ pear fruits aroma quality. • 189 DAMs and 12,032 DEGs were identified. • ‘Hongnanguo’ pollinizer increased the content of ABA, IAA, and ethylene. • Established a possible regulatory network of the mechanism of xenia effect on pear aroma formation. The flavor of ‘Yali’ pear fruits has substantially declined recently as a result of poor pollination tree selection. Xenia effect is a powerful mechanism for regulating aroma production. To study the effect of different pollens on aroma quality and the molecular basis of xenia effect in ‘Yali’ pear fruits, ‘Hongnanguo’ and ‘Xuehuali’ were used as pollinizers, and the hybrid fruits were named YH and YX, respectively. Metabolome, transcriptome, volatile compounds, and hormone were jointly analyzed in YH and YX peels with three ripening stages. After pollinating with ‘Hongnanguo’ pollen, the contents of total aroma, esters and nerolidol, the odor activity value of characteristic volatiles in YH were significantly increased, compared with the aroma character of the pollinizer cultivars, indicating ‘Hongnanguo’ pollinizer has a xenia effect on ‘Yali’ pear fruits aroma quality. Further, the content of ABA, IAA, and ethylene reveal the differences during aroma formation between YH and YX. 189 differentially accumulated metabolites (DAMs) and 12,032 differentially expressed genes (DEGs) were identified. Based on co-expression network analysis, network maps of ‘Yali’ pear aroma-related DEGs were generated. We surmise aroma biosynthesis genes ( ADH, ALDH, NES , and FPS ), ABA, IAA, ethylene signal transduction, and several transcription factors play important roles in the xenia effect.