Unraveling a Small Secreted Peptide SUBPEP3 That Positively Regulates Salt-Stress Tolerance in Pyrus betulifolia.

Small secreted peptides (SSPs) play important roles in regulating plants' growth and development in response to external stimulus, but the genes and functions of SSPs in many species are still unknown. Therefore, it is particularly significant to characterize and annotate SSP genes in plant genomes. As a widely used stock of pears, Pyrus betulifolia has strong resistance to biotic and abiotic stresses. In this study, we analyzed the SSPs genes in the genome of P. betulifolia according to their characteristics and homology. A total of 1195 SSP genes were identified, and most of them are signaling molecules. Among these, we identified a new SSP, subtilase peptide 3 (SUBPEP3), which derived from the PA region of preSUBPEP3, increasing the expression level under salt stress. Both adding synthetic peptide SUBPEP3 to the culture medium of pears and the overexpression of SUBPEP3 in tobacco can improve the salt tolerance of plants. In summary, we annotated the SSP genes in the P. betulifolia genome and identified a small secreted peptide SUBPEP3 that regulates the salt tolerance of P. betulifolia, which provides an important theoretical basis for further revealing the function of SSPs.

Inhibition of PbeXTH1 and PbeSEOB1 is required for the Valsa canker resistance contributed by Wall-associated kinase gene MbWAK1.

Wall-associated kinases (WAKs) have been determined to recognize pathogenic signals and initiate plant immune responses. However, the roles of the family members in host resistance against Valsa canker, a serious fungal disease of apples and pears, are largely unknown. Here, we identified MbWAK1 in Malus baccata, a resistant germplasm differentially expressed during infection by Valsa mali (Vm). Over-expression of MbWAK1 enhanced the Valsa canker resistance of apple and pear fruits and 'Duli-G03' (Pyrus betulifolia) suspension cells. A large number of phloem, cell wall, and lipid metabolic process-related genes were differentially expressed in overexpressed suspension cell lines in response to Valsa pyri (Vp) signals. Among these, the expression of xyloglucan endotransglucosylase/hydrolase (XTH) gene PbeXTH1 and sieve element occlusion B-like (SEOB) gene PbeSEOB1 were significantly inhibited. Transient expression of PbeXTH1 or PbeSEOB1 compromised the expressional induction of MbWAK1 and the resistance contributed by MbWAK1. In addition, PbeXTH1 and PbeSEOB1 suppressed the immune response induced by MbWAK1. Our results enriched the molecular mechanisms for MbWAK1 against Valsa canker and resistant breeding.

Assessment and Partial Characterization of Candidate Genes in Dihydrochalcone and Arbutin Biosynthesis in an Apple-Pear Hybrid by De Novo Transcriptome Assembly.

Apples (Malus × domestica Borkh.) and pears (Pyrus communis L.) are valuable crops closely related within the Rosaceae family with reported nutraceutical properties derived from secondary metabolites including phloridzin and arbutin, which are distinctive phenolic metabolites characterizing apples and pears, respectively. Here, we generated a de novo transcriptome assembly of an intergeneric hybrid between apple and pear, accumulating intermediate levels of phloridzin and arbutin. Combining RNA-seq, in silico functional annotation prediction, targeted gene expression analysis, and expression-metabolite correlations, we identified candidate genes for functional characterization, resulting in the identification of active arbutin synthases in the hybrid and parental genotypes. Despite exhibiting an active arbutin synthase in vitro, the natural lack of arbutin in apples is reasoned by the absence of the substrate and broad substrate specificity. Altogether, our study serves as the basis for future assessment of potential physiological roles of identified genes by genome editing of hybrids and pears.

Comparative analysis of POD genes and their expression under multiple hormones in Pyrus bretschenedri.

BACKGROUND: Class III peroxidase (POD) enzymes play vital roles in plant development, hormone signaling, and stress responses. Despite extensive research on POD families in various plant species, the knowledge regarding the POD family in Chinese pear (Pyrus bretschenedri) is notably limited. RESULTS: We systematically characterized 113 POD family genes, designated as PbPOD1 to PbPOD113 based on their chromosomal locations. Phylogenetic analysis categorized these genes into seven distinct subfamilies (I to VII). The segmental duplication events were identified as a prevalent mechanism driving the expansion of the POD gene family. Microsynteny analysis, involving comparisons with Pyrus bretschenedri, Fragaria vesca, Prunus avium, Prunus mume and Prunus persica, highlighted the conservation of duplicated POD regions and their persistence through purifying selection during the evolutionary process. The expression patterns of PbPOD genes were performed across various plant organs and diverse fruit development stages using transcriptomic data. Furthermore, we identified stress-related cis-acting elements within the promoters of PbPOD genes, underscoring their involvement in hormonal and environmental stress responses. Notably, qRT-PCR analyses revealed distinctive expression patterns of PbPOD genes in response to melatonin (MEL), salicylic acid (SA), abscisic acid (ABA), and methyl jasmonate (MeJA), reflecting their responsiveness to abiotic stress and their role in fruit growth and development. CONCLUSIONS: In this study, we investigated the potential functions and evolutionary dynamics of PbPOD genes in Pyrus bretschenedri, positioning them as promising candidates for further research and valuable indicators for enhancing fruit quality through molecular breeding strategies.

Ascorbic acid releases dormancy and promotes germination by an integrated regulation of abscisic acid and gibberellin in Pyrus betulifolia seeds.

Seed dormancy is an important life history state in which intact viable seeds delay or prevent germination under suitable conditions. Ascorbic acid (AsA) acts as a small molecule antioxidant, and breaking seed dormancy and promoting subsequent growth are among its numerous functions. In this study, a germination test using Pyrus betulifolia seeds treated with exogenous AsA or AsA synthesis inhibitor lycorine (Lyc) and water absorption was conducted. The results indicated that AsA released dormancy and increased germination and 20 mmol L-1 AsA promoted cell division, whereas Lyc reduced germination. Seed germination showed typical three phases of water absorption; and seeds at five key time points were sampled for transcriptome analysis. It revealed that multiple pathways were involved in breaking dormancy and promoting germination through transcriptome data, and 12 differentially expressed genes (DEGs) related to the metabolism and signal transduction of abscisic acid (ABA) and gibberellins (GA) were verified by subsequent RT-qPCR. For metabolites, exogenous AsA increased endogenous AsA and GA3 but reduced ABA and the ABA/GA3 ratio. In addition, three genes regulating ABA synthesis were downregulated by AsA, while five genes mediating ABA degradation were upregulated. Taken together, AsA regulates the pathways associated with ABA and GA synthesis, catalysis, and signal transduction, with subsequent reduction in ABA and increase in GA and further the balance of ABA/GA, ultimately releasing dormancy and promoting germination.

Endoglucanase H from Aspergillus westerdijkiae Plays an Important Role in the Virulence on Pear Fruits.

Aspergillus westerdijkiae can infect many agricultural products including cereals, grapes, and pear. Pathogenic fungi secrete diverse effectors as invasive weapons for successful invasion the host plant. During the pathogen-host interaction, 4486 differentially expressed genes were observed in A. westerdijkiae with 2773 up-regulated and 1713 down-regulated, whereas 8456 differentially expressed genes were detected in pear fruits with 4777 up-regulated and 3679 down-regulated. A total of 309 effector candidate genes were identified from the up-regulated genes in A. westerdijkiae. Endoglucanase H (AwEGH) was significantly induced during the pathogen-host interaction. Deletion of AwEGH resulted in altered fungal growth and morphology and reduced conidia production and germination compared to the wild-type. Further experiments demonstrated that AwEGH plays a role in cell wall integrity. Importantly, disruption of AwEGH significantly reduced the fungal virulence on pear fruits, and this defect can be partly explained by the impaired ability of A. westerdijkiae to penetrate host plants.

Comparative physiological and transcriptomic analysis reveals an improved biological control efficacy of Sporidiobolus pararoseus Y16 enhanced with ascorbic acid against the oxidative stress tolerance caused by Penicillium expansum in pears.

Sporidiobolus pararoseus Y16, a species of significant ecological importance, has distinctive physiological and biological regulatory systems that aid in its survival and environmental adaptation. The goal of this investigation was to understand the complex interactions between physiological and molecular mechanisms in pear fruits as induced by S. pararoseus Y16. The study investigated the use of S. pararoseus Y16 and ascorbic acid (VC) in combination in controlling blue mold decay in pears via physiological and transcriptomic approach. The study results showed that treatment of S. pararoseus Y16 with 150 µg/mL VC reduced pears blue mold disease incidence from 43% to 11%. Furthermore, the combination of S. pararoseus Y16 and VC significantly inhibited mycelia growth and spore germination of Penicillium expansum in the pear's wounds. The pre-treatment did not impair post-harvest qualities of pear fruit but increased antioxidant enzyme activity specifically polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT) activities as well as phenylalanine ammonia-lyase (PAL) enzyme activity. The transcriptome analysis further uncovered 395 differentially expressed genes (DEGs) and pathways involved in defense mechanisms and disease resistance. Notable pathways of the DEGs include plant-pathogen interaction, tyrosine metabolism, and hormone signal transduction pathways. The integrative approach with both physiological and transcriptomic tools to investigate postharvest pathology in pear fruits with clarification on how S. pararoseus Y16 enhanced with VC, improved gene expression for disease defense, and create alternative controls strategies for managing postharvest diseases.

The PbbHLH62/PbVHA-B1 module confers salt tolerance through modulating intracellular Na+/K+ homeostasis and reactive oxygen species removal in pear.

The vacuolar H+-ATPase (V-ATPase) is a multi-subunit membrane protein complex, which plays pivotal roles in building up an electrochemical H+-gradient across tonoplast, energizing Na+ sequestration into the central vacuole, and enhancing salt stress tolerance in plants. In this study, a B subunit of V-ATPase gene, PbVHA-B1 was discovered and isolated from stress-induced P. betulaefolia combining with RT-PCR method. The RT-qPCR analysis revealed that the expression level of PbVHA-B1 was upregulated by salt, drought, cold, and exogenous ABA treatment. Subcellular localization analyses showed that PbVHA-B1 was located in the cytoplasm and nucleus. Moreover, overexpression of PbVHA-B1 gene noticeably increased the ATPase activity and the tolerance to salt in transgenic Arabidopsis plants. In contrast, knockdown of PbVHA-B1 gene in P.betulaefolia by virus-induced gene silencing had reduced resistance to salt stress. In addition, using yeast one-hybride (Y1H) and yeast two-hybride (Y2H) screens, PbbHLH62, a bHLH transcription factor, was identified as a partner of the PbVHA-B1 promoter and protein. Then, we also found that PbbHLH62 positively regulate the expression of PbVHA-B1 and the ATPase activity after salt stress treatment. These findings provide evidence that PbbHLH62 played a critical role in the salt response. Collectively, our results demonstrate that a PbbHLH62/PbVHA-B1 module plays a positive role in salt tolerance by maintain intracellular ion and ROS homeostasis in pear.

Isolation and Characterization of a Lytic Bacteriophage RH-42-1 of Erwinia amylovora from Orchard Soil in China.

Fire blight, caused by the bacterium Erwinia amylovora, is a major threat to pear production worldwide. Bacteriophages, viruses that infect bacteria, are a promising alternative to antibiotics for controlling fire blight. In this study, we isolated a novel bacteriophage, RH-42-1, from Xinjiang, China. We characterized its biological properties, including host range, plaque morphology, infection dynamics, stability, and sensitivity to various chemicals. RH-42-1 infected several E. amylovora strains but not all. It produced clear, uniform plaques and exhibited optimal infectivity at a multiplicity of infection (MOI) of 1, reaching a high titer of 9.6 × 109 plaque-forming units (PFU)/mL. The bacteriophage had a short latent period (10 min), a burst size of 207 PFU/cell, and followed a sigmoidal one-step growth curve. It was stable at temperatures up to 60 °C but declined rapidly at higher temperatures. RH-42-1 remained viable within a pH range of 5 to 9 and was sensitive to extreme pH values. The bacteriophage demonstrates sustained activity upon exposure to ultraviolet radiation for 60 min, albeit with a marginal reduction. In our assays, it exhibited a certain level of resistance to 5% chloroform (CHCl3), 5% isopropanol (C3H8O), and 3% hydrogen peroxide (H2O2), which had little effect on its activity, whereas it showed sensitivity to 75% ethanol (C2H5OH). Electron microscopy revealed that RH-42-1 has a tadpole-shaped morphology. Its genome size is 14,942 bp with a GC content of 48.19%. Based on these characteristics, RH-42-1 was identified as a member of the Tectiviridae family, Alphatectivirus genus. This is the first report of a bacteriophage in this genus with activity against E. amylovora.

PbARF19-mediated auxin signaling regulates lignification in pear fruit stone cells.

The stone cells in pear fruits cause rough flesh and low juice, seriously affecting the taste. Lignin has been demonstrated as the main component of stone cells. Auxin, one of the most important plant hormone, regulates most physiological processes in plants including lignification. However, the concentration effect and regulators of auxin on pear fruits stone cell formation remains unclear. Here, endogenous indole-3-acetic acid (IAA) and stone cells were found to be co-localized in lignified cells by immunofluorescence localization analysis. The exogenous treatment of different concentrations of IAA demonstrated that the application of 200 µM IAA significantly reduced stone cell content, while concentrations greater than 500 µM significantly increased stone cell content. Besides, 31 auxin response factors (ARFs) were identified in pear genome. Putative ARFs were predicted as critical regulators involved in the lignification of pear flesh cells by phylogenetic relationship and expression analysis. Furthermore, the negative regulation of PbARF19 on stone cell formation in pear fruit was demonstrated by overexpression in pear fruitlets and Arabidopsis. These results illustrated that the PbARF19-mediated auxin signal plays a critical role in the lignification of pear stone cell by regulating lignin biosynthetic genes. This study provides theoretical and practical guidance for improving fruit quality in pear production.

Increased DNA methylation contributes to the early ripening of pear fruits during domestication and improvement.

BACKGROUND: DNA methylation is an essential epigenetic modification. However, its contribution to trait changes and diversity in the domestication of perennial fruit trees remains unknown. RESULTS: Here, we investigate the variation in DNA methylation during pear domestication and improvement using whole-genome bisulfite sequencing in 41 pear accessions. Contrary to the significant decrease during rice domestication, we detect a global increase in DNA methylation during pear domestication and improvement. We find this specific increase in pear is significantly correlated with the downregulation of Demeter-like1 (DML1, encoding DNA demethylase) due to human selection. We identify a total of 5591 differentially methylated regions (DMRs). Methylation in the CG and CHG contexts undergoes co-evolution during pear domestication and improvement. DMRs have higher genetic diversity than selection sweep regions, especially in the introns. Approximately 97% of DMRs are not associated with any SNPs, and these DMRs are associated with starch and sucrose metabolism and phenylpropanoid biosynthesis. We also perform correlation analysis between DNA methylation and gene expression. We find genes close to the hypermethylated DMRs that are significantly associated with fruit ripening. We further verify the function of a hyper-DMR-associated gene, CAMTA2, and demonstrate that overexpression of CAMTA2 in tomato and pear callus inhibits fruit ripening. CONCLUSIONS: Our study describes a specific pattern of DNA methylation in the domestication and improvement of a perennial pear tree and suggests that increased DNA methylation plays an essential role in the early ripening of pear fruits.

Enhancing the flavour quality of Laiyang pear wine by screening sorbitol-utilizing yeasts and co-fermentation strategies.

This study took a novel approach to address the dual challenges of enhancing the ethanol content and aroma complexity in Laiyang pear wine. It focused on sorbitol as a pivotal element in the strategic selection of yeasts with specific sorbitol-utilization capabilities and their application in co-fermentation strategies. We selected two Saccharomyces cerevisiae strains (coded as Sc1, Sc2), two Metschnikowia pulcherrima (coded as Mp1, Mp2), and one Pichia terricola (coded as Tp) due to their efficacy as starter cultures. Notably, the Sc2 strain, alone or with Mp2, significantly increased the ethanol content (30% and 16%). Mixed Saccharomyces cerevisiae and Pichia terricola fermentation improved the ester profiles and beta-damascenone levels (maximum of 150%), while Metschnikowia pulcherrima addition enriched the phenethyl alcohol content (maximum of 330%), diversifying the aroma. This study investigated the efficacy of strategic yeast selection based on sorbitol utilization and co-fermentation methods in enhancing Laiyang pear wine quality and aroma.

In vitro digestion properties of Laiyang pear residue polysaccharides and it counteracts DSS-induced gut injury in mice via modulating gut inflammation, gut microbiota and intestinal barrier.

The aim of this study was to explore the dynamic changes in the physicochemical properties of Laiyang pear residue polysaccharide (LPP) during in vitro digestion, as well as its protective effect on the intestines. Monosaccharide composition and molecular weight analysis showed that there was no significant change in LPP during the oral digestion stage. However, during the gastric and intestinal digestion stages, the glycosidic bonds of LPP were broken, leading to the dissociation of large molecular aggregates and a significant increase in reducing sugar content (CR) accompanied by a decrease in molecular weight. In addition, LPP exerted the intestinal protective ability via inhibiting gut inflammation, improving intestinal barrier, and regulating intestinal flora in DSS-induced mice. Specifically, LPP mitigated DSS-induced intestinal pathological damage of mice via enhancing intestinal barrier integrity and upregulating expressions of TJ proteins, and suppressed inflammation by inhibiting NF-κB signaling axis. Furthermore, LPP decreased the ratio of Firmicutes/Bacteroidetes, increased the relative abundance of Lactobacillus, and altered the diversity and the composition of gut microbiota in DSS-induced mice. Therefore, LPP had the potential to be a functional food that improved gut microbiota environment to enhance health and prevent diseases, such as a prebiotic.

Combining transfer learning and hyperspectral imaging to identify bruises of pears across different bruise types.

Mechanical bruise is one of the most crucial factors affecting the quality of pears, which has a huge influence on postharvest transportation, storage, and sale of pears. To rapidly detect early bruises of pears across different bruise types, hyperspectral imaging technology coupled with transfer learning methods was performed in this study. Two transfer learning methods, that is, transfer component analysis (TCA) and manifold embedded distribution alignment (MEDA), were applied for two tasks (impact bruise â†’ crush bruise, crush bruise â†’ impact bruise). Supporting vector machine (SVM) was set as a baseline to conduct analysis and comparison of the transferability of the models. The result showed that, for task 1 (impact bruise â†’ crush bruise), MEDA and TCA-SVM model achieved a classification accuracy of 93.33% and 91.11% in target domain, individually. For task 2 (crush bruise â†’impact bruise), MEDA and TCA-SVM model achieved an accuracy of 88.89% and 85.19% in target domain, respectively. Both the two models improved the accuracy compared with SVM models (84.44% for task 1; 77.04% for task 2). Overall, the results indicated that transfer learning approaches could perform pear bruise detection across different bruise types. Hyperspectral imaging in combination with transfer learning methods is a promising possibility for the efficient and cost-saving field detection of fruit bruises among different bruise types. PRACTICAL APPLICATION: The production and export of pears are faced with problems of mechanical damage due to vibration, collision, impact, and other factors, which cause chemical changes in color, odor, and taste. Sometimes the bruise was too slight to be ignored which would infect with other fruits in the future. In this study, we used hyperspectral imaging combined with transfer learning method could detect these slight bruises caused by different factors. Distinguishing different types of damage can provide a reference for quick judgment of the process causing damage and take prompt measures to reduce economic losses.

A novel fluorescent probe with a large Stokes shift for colorimetric and selective detection of cysteine in water, milk, cucumber, pear and tomato.

Cysteine is an important amino acid that is related to human health and food safety. How to effectively detect Cys in food has received widespread attention. Compared with other methods, fluorescent probes have the advantages of simple operation, high sensitivity, and good selectivity. Therefore, a selective fluorescence probe 2 for Cys in food was designed and synthesized. Probe 2 employed the acrylate group as a thiol-recognition site for Cys, which endowed probe 2 with better selectivity for Cys over Hcy and GSH. The recognition pathway underwent Michael addition, intramolecular cyclization, and concomitant release of the piperideine-based fluorophore, along with a chromogenic change from yellow to orange. This pathway was supported by 1H NMR analysis and DFT calculations. In addition, probe 2 displays a linear response to Cys concentrations (0-30 µM), low detection limit (0.89 µM), and large Stokes shift (125 nm). Overall, probe 2 showed great application potential for the quantitative determination of Cys in water, milk, cucumber, pear and tomato.

Identification of Mycoviruses in the Pathogens of Fragrant Pear Valsa Canker from Xinjiang in China.

As a common disease, canker seriously affects the yield and quality of fragrant pear due to the lack of effective control measures. Some fungi have been reported to harbor rich reservoirs of viral resources, and some mycoviruses can be used as biocontrol agents against plant diseases. In this study, 199 isolates were obtained from diseased branches of fragrant pear in the main production areas of Xinjiang. Among them, 134 belonged to Valsa spp., identified using morphological and molecular biological techniques, in which V. mali was the dominant species. The mycoviruses in Valsa spp. were further identified using metatranscriptomic sequencing and RT-PCR. The results revealed that a total of seven mycoviruses were identified, belonging to Botourmiaviridae, Endornaviridae, Fusariviridae, Hypoviridae, Mitoviridae, and Narnaviridae, among which Phomopsis longicolla hypovirus (PlHV) was dominant in all the sample collection regions. The Cryphonectria hypovirus 3-XJ1 (CHV3-XJ1), Botourmiaviridae sp.-XJ1 (BVsp-XJ1), and Fusariviridae sp.-XJ1 (Fvsp-XJ1) were new mycoviruses discovered within the Valsa spp. More importantly, compared with those in the virus-free Valsa spp. strain, the growth rate and virulence of the VN-5 strain co-infected with PlHV and CHV3-XJ1 were reduced by 59% and 75%, respectively, and the growth rate and virulence of the VN-34 strain infected with PlHV were reduced by 42% and 55%, respectively. On the other hand, the horizontal transmission efficiency of PlHV decreased when PlHV was co-infected with CHV3-XJ1, indicating that PlHV and CHV3-XJ1 were antagonistic. In summary, the mycoviruses in Valsa spp. were identified in Xinjiang for the first time, and three of them were newly discovered mycoviruses, with two strains yielding good results. These results will offer potential biocontrol resources for managing pear canker disease and provide a theoretical basis for the control of fruit tree Valsa canker disease.

The seed dispersal syndrome hypothesis in ungulate-dominated landscapes.

The Seed Dispersal Syndrome Hypothesis (SDSH) posits that fruit traits predict the main dispersers interacting with plant species. Mammalian dispersers, relying heavily on olfactory cues, are expected to select dull-colored, scented, and larger fruits compared to birds. However, challenges like overabundant seed predators and context-dependency of frugivore-plant interactions complicate SDSH expectations. We studied the Iberian pear, Pyrus bourgaeana, an expected mammal-dispersed tree based on its fruit traits. Extensive camera-trapping data (over 35,000 records) from several tree populations and years revealed visits from seven frugivore groups, with ungulate fruit predators (59-97%) and carnivore seed dispersers (1-20%) most frequent, while birds, lagomorphs, and rodents were infrequent (0-10%). Red deer and wild boar were also the main fruit removers in all sites and years but acted as fruit and seed predators, and thus likely exert conflicting selection pressures to those exerted by seed dispersers. Although, as predicted by the SDSH, most Iberian pear fruits were consumed by large and medium-sized mammals, the traits of Iberian pear fruits likely reflect selection pressures from dispersal vectors in past times. Our results do not challenge the SDHS but do reveal the importance of considering frugivore functional roles for its adequate evaluation.

Sucrose, cell wall, and polyamine metabolisms involve in preserving postharvest quality of 'Zaosu' pear fruit by L-glutamate treatment.

'Zaosu' pear fruit is prone to yellowing of the surface and softening of the flesh after harvest. This work was performed to assess the influences of L-glutamate treatment on the quality of 'Zaosu' pears and elucidate the underlying mechanisms involved. Results demonstrated that L-glutamate immersion reduced ethylene release, respiratory intensity, weight loss, brightness (L*), redness (a*), yellowness (b*), and total coloration difference (ΔE); enhanced ascorbic acid, soluble solids, and soluble sugar contents; maintained chlorophyll content and flesh firmness of pears. L-glutamate also restrained the activities of neutral invertase and acid invertase, while enhancing sucrose phosphate synthetase and sucrose synthase activities to facilitate sucrose accumulation. The transcriptions of PbSGR1, PbSGR2, PbCHL, PbPPH, PbRCCR, and PbNYC were suppressed by L-glutamate, resulting in a deceleration of chlorophyll degradation. L-glutamate concurrently suppressed the transcription levels and enzymatic activities of polygalacturonases, pectin methylesterases, cellulase, and ß-glucosidase. It restrained polygalacturonic acid trans-eliminase and pectin methyl-trans-eliminase activities as well as inhibited the transcription levels of PbPL and Pbß-gal. Moreover, the gene transcriptions and enzymatic activities of arginine decarboxylase, ornithine decarboxylase, S-adenosine methionine decarboxylase, glutamate decarboxylase, γ-aminobutyric acid transaminase, glutamine synthetase along with the PbSPDS transcription was promoted by L-glutamate. L-glutamate also resulted in the down-regulation of PbPAO, PbDAO, PbSSADH, PbGDH, and PbGOGAT transcription levels, while enhancing γ-aminobutyric acid, glutamate, and pyruvate acid contents in pears. These findings suggest that L-glutamate immersion can effectively maintain the storage quality of 'Zaosu' pears via modulating key enzyme activities and gene transcriptions involved in sucrose, chlorophyll, cell wall, and polyamine metabolism.

Transcriptome and metabolome profiling reveal the effects of hormones on current-year shoot growth in Chinese 'Cuiguan' pear grafted onto vigorous rootstock 'Duli' and dwarf rootstock 'Quince A'.

BACKGROUND: Dwarf rootstocks have important practical significance for high-density planting in pear orchards. The shoots of 'Cuiguan' grafted onto the dwarf rootstock were shorter than those grafted onto the vigorous rootstock. However, the mechanism of shorter shoot formation is not clear. RESULTS: In this study, the current-year shoot transcriptomes and phytohormone contents of 'CG‒QA' ('Cuiguan' was grafted onto 'Quince A', and 'Hardy' was used as interstock) and 'CG‒DL' ('Cuiguan' was grafted onto 'Duli', and 'Hardy' was used as interstock) were compared. The transcriptome results showed that a total of 452 differentially expressed genes (DEGs) were identified, including 248 downregulated genes and 204 upregulated genes; the plant hormone signal transduction and zeatin biosynthesis pathways were significantly enriched in the top 20 KEGG enrichment terms. Abscisic acid (ABA) was the most abundant hormone in 'CG‒QA' and 'CG‒DL'; auxin and cytokinin (CTK) were the most diverse hormones; additionally, the contents of ABA, auxin, and CTK in 'CG‒DL' were higher than those in 'CG‒QA', while the fresh shoot of 'CG‒QA' accumulated more gibberellin (GA) and salicylic acid (SA). Metabolome and transcriptome co-analysis identified three key hormone-related DEGs, of which two (Aldehyde dehydrogenase gene ALDH3F1 and YUCCA2) were upregulated and one (Cytokinin oxidase/dehydrogenase gene CKX3) was downregulated. CONCLUSIONS: Based on the results of transcriptomic and metabolomic analysis, we found that auxin and CTK mainly regulated the shoot differences of 'CG-QA' and 'CG-DL', and other hormones such as ABA, GA, and SA synergistically regulated this process. Three hormone-related genes ALDH3F1, YUCCA2, and CKX3 were the key genes contributing to the difference in shoot growth between 'CG-QA' and 'CG-DL' pear. This research provides new insight into the molecular mechanism underlying shoot shortening after grafted onto dwarf rootstocks.

Genome-wide identification of GA2ox genes family and analysis of PbrGA2ox1-mediated enhanced chlorophyll accumulation by promoting chloroplast development in pear.

BACKGROUND: Chlorophyll (Chl) is an agronomic trait associated with photosynthesis and yield. Gibberellin 2-oxidases (GA2oxs) have previously been shown to be involved in Chl accumulation. However, whether and how the PbrGA2ox proteins (PbrGA2oxs) mediate Chl accumulation in pear (Pyrus spp.) is scarce. RESULTS: Here, we aimed to elucidate the role of the pear GA2ox gene family in Chl accumulation and the related underlying mechanisms. We isolated 13 PbrGA2ox genes (PbrGA2oxs) from the pear database and identified PbrGA2ox1 as a potential regulator of Chl accumulation. We found that transiently overexpressing PbrGA2ox1 in chlorotic pear leaves led to Chl accumulation, and PbrGA2ox1 silencing in normal pear leaves led to Chl degradation, as evident by the regreening and chlorosis phenomenon, respectively. Meanwhile, PbrGA2ox1-overexpressing (OE) tobacco plants discernably exhibited Chl built-up, as evidenced by significantly higher Pn and Fv/Fm. In addition, RNA sequencing (RNA-seq), physiological and biochemical investigations revealed an increase in abscisic acid (ABA), methyl jasmonate (MeJA), and salicylic acid (SA) concentrations and signaling pathways; a marked elevation in reducing and soluble sugar contents; and a marginal decline in the starch and sucrose levels in OE plants. Interestingly, PbrGA2ox1 overexpression did not prominently affect Chl synthesis. However, it indeed facilitated chloroplast development by increasing chloroplast number per cell and compacting the thylakoid granum stacks. These findings might jointly contribute to Chl accumulation in OE plants. CONCLUSION: Overall, our results suggested that GA2oxs accelerate Chl accumulation by stimulating chloroplast development and proved the potential of PbrGA2ox1 as a candidate gene for genetically breeding biofortified pear plants with a higher yield.