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[Introduction] The 3.7 GHz high-power TH2103A klystrons are widely used in the tokamak experimental device. To simplify the HV power supply system (removing the vacuum tetrode in the anode modulation), a power supply mode based on voltage division mode is introduced into the TH2103A klystron of the HL-2A device. To operate the klystron safely in this power supply mode, a system for measuring and protecting the anode current of TH2103A klystron is developed. [Method] According to the analysis of the characteristics of the anode current in this power supply mode, the anode current showed the condition of normal, forward overcurrent, or reverse overcurrent. In the case of forward overcurrent or reverse overcurrent, it meant that many electrons were bombarding or flowing out of the anode. They were very dangerous to the klystron, which usually may cause overcurrent of the klystron titanium pump, or even damage the klystron. Therefore it was important to accurately measure the anode current and cut off the high voltage to protect the klystron in case of overcurrent. The principle and power supply mode and the principle and implementation plan of the anode protection system were described in this paper. [Result] In this paper, the effectiveness and reliability of the anode current measurement and protection system were confirmed. [Conclusion] The power supply mode and the anode current measurement and protection system of this paper are of important reference significance for the operation and maintenance of TH2103A klystron.

As a cell proliferation regulator involved in wide biological processes in plants, GRF-INTERACTING FACTOR (GIF) controls different tissues development. However, whether GIF participates in fruit development remains unclear. According to transcriptome data, we identified PbGIF1 was highly expressed during fruit development in cytokinins induced parthenocarpy pear. In the present study, the biofunction of PbGIF1 was initially verified. Overexpression of PbGIF1 promoted fruit size of transgenic tomato. The size of flesh fruit was not affected by cell expansion but the cell proliferation was promoted by overexpressing PbGIF1. The accelerated cell proliferation process was also observed in PbGIF1-overexpressed transgenic pear fruit calli. The transcriptional regulation of cytokinins on PbGIF1 was further confirmed by exogenous CPPU treatments in pear fruitlets. To investigate the underlying mechanism, the cytokinins-responded factor, PbRR1, was further focused on. The results of Yeast-one-hybrid assay suggested that PbRR1 can bind to the promoter sequence of PbGIF1. The transcriptional activation of PbRR1 on PbGIF1 was also confirmed by Dual-Luciferase assays. Taken together, the results showed that cytokinins control pear fruit development via the transcriptional activation of PbGIF1 by PbRR1.

B-class MADS-box genes are sufficient for the specification of petals and stamens; however, the role of Tomato MADS-box protein 6 (TM6) in seed formation in pear remains largely unknown. In this study, PbTM6a and PbTM6b, characterized as negative regulators of the response to GA4+7, were identified as classic B-class MADS-box genes. Additionally, both of the genes encoding proteins carried the highly conserved MADS-box domain, and showed high expression levels in anther, petal and filament of 'Dangshansu'. Overexpression of PbTM6a in tomato reduced the number of seeds per fruit. Analysis of the anatomical structure of floral organs revealed that the reduction in seed number in transgenic fruits might be attributed to an obstacle of pollen release due to strongly formed stomium and limited ovary space of ovule development. Moreover, triphenyl tetrazolium chloride (TTC) staining and in vitro germination tests of pollen grains indicated that PbTM6a overexpression reduced pollen viability and germination rates. Reciprocal crosses showed that the reduction in seed number in transgenic fruits was dominantly caused by the decreased fertility of pollen grains. Subsequent scanning electron microscopy showed that sterile pollen grains were caused by abnormal pollen grains. Additionally, the reduced levels of jasmonic acid (JA), abscisic acid (ABA), indole-3-acetic acid (IAA) and gibberellin A3 (GA3) in transgenic stamens contributed to the development of sterile pollen. Collectively, our results reveal the role of PbTM6a genes in controlling male infertility and broaden our understanding of the mechanism underlying the function of B-class MADS-box genes in pear.

The red color of the pear peel in red-skinned European pear is due to the accumulation of anthocyanins. Numerous transcription factors play pivotal roles in anthocyanin biosynthesis, with zinc finger proteins frequently implicated in the regulation of this process via MYB10, as documented in earlier studies. In this article, we identified a zinc finger protein gene, named PbZAT12, that does not rely on PbMYB10, to regulate anthocyanin biosynthesis. The PbZAT12 protein was localized within the nucleus and exhibited a positive influence on the accumulation of anthocyanins in the peel of ‘Red Zaosu’ pears. Moreover, overexpression of PbZAT12 resulted in a significant up-regulation of PbDFR, PbANS, and PbUFGT expression levels in pear fruitlets. Y1H assays demonstrated a direct binding ability of PbZAT12 to proPbDFR, proPbANS, and proPbUFGT, which was supported by a dual luciferase assay, indicating its potential to activate the transcriptional activity of these promoters. However, in contrast to its effect on the aforementioned promoters, PbZAT12 did not exhibit an activation of PbMYB10. In summary, our findings suggest that a zinc finger transcription factor, PbZAT12, exerts a positive influence on anthocyanin biosynthesis in pear fruit through direct upregulation of the expression levels of PbDFR, PbANS, and PbUFGT.

Abstract Background Decrease in anthocyanin content results in the loss of red color in leaves, petals and receptacles during development. The content of anthocyanin was affected by the biosynthesis and degradation of anthocyanin. Compared with the known detailed mechanism of anthocyanin biosynthesis, the degradation mechanism is not fully investigated. It is vital to study the degradation mechanism of anthocyanin in pear for promoting the accumulation of anthocyanin and inhibiting the red fading in pear. Results Here, we reported that laccase encoded by PbLAC4-like was associated with anthocyanin degradation in pear. The expression pattern of PbLAC4-like was negatively correlated with the content of anthocyanin during the color fading process of pear leaves, petals and receptacles. Phylogenetic analysis and sequence alignment revealed that PbLAC4-like played a vital role in anthocyanin degradation. Thus, the degradation of anthocyanin induced by PbLAC4-like was further verified by transient assays and prokaryotic expression. More than 80% of anthocyanin compounds were degraded by transiently over-expressed PbLAC4-like in pear fruitlet peel. The activity of crude enzyme to degrade anthocyanin in leaves at different stages was basically consistent with the expression of PbLAC4-like. The anthocyanin degradation ability of prokaryotic induced PbLAC4-like protein was also verified by enzyme activity assay. Besides, we also identified PbMYB26 as a positive regulator of PbLAC4-like. Yeast one-hybrid and dual luciferase assay results showed that PbMYB26 activated PbLAC4-like expression by directly binding to the PbLAC4-like promoter. Conclusions Taken together, the PbLAC4-like activated by PbMYB26, was involved in the degradation of anthocyanin, resulting in the redness fading in different pear tissues.

The red flesh in apple fruit is a desired trait by consumers and it is associated to the anthocyanin content, which is mainly controlled by MdMYB10 with a R6 promoter. In this study, a high-density linkage group was constructed using the ‘Fuji’ x ‘Red3’ population which contained homozygous alleles R1R1 and R6R6, respectively. The linkage group consists of 7 630 SNPs along 17 linkage groups, spanning 2 270.21 cM, with an average density of 0.30 cM per marker. The cyanidin-3-galactoside concentration was used as the phenotypic data in QTL analysis. Moreover, one QTL peak which was flaked by two markers, marker2187260 to marker2173766, with LOD scores of 4.49 was detected. This QTL ranged from 0 to 40.79 cM on the top of linkage group (LG16). In addition one candidate molecular marker (marker2175442) in this QTL was identified, which was significant correlated with the flesh cyanidin-3-galactoside concentration. These genetic findings enrich the breeding basis of fruit flesh coloration in apple.

Abstract Background Parthenocarpy results in traits attractive to both consumers and breeders, and it overcomes the obstacle of self-incompatibility in the fruit set of horticultural crops, including pear (Pyrus bretshneider). However, there is limited knowledge regarding the genetic and molecular mechanisms that regulate parthenogenesis. Results Here, in a transcriptional comparison between pollination-dependent fruit and GA4-induced parthenocarpy, PbCYP78A6 was identified and proposed as a candidate gene involved in parthenocarpy. PbCYP78A6 is similar to Arabidopsis thaliana CYP78A6 and highly expressed in pear hypanthia. The increased PbCYP78A6 expression, as assessed by RT-qPCR, was induced by pollination and GA4 exposure. The ectopic overexpression of PbCYP78A6 contributed to parthenocarpic fruit production in tomato. The PbCYP78A6 expression coincided with fertilized and parthenocarpic fruitlets development and the expression of fruit development-related genes as assessed by cytological observations and RT-qPCR, respectively. PbCYP78A6 RNA interference and overexpression in pear calli revealed that the gene is an upstream regulator of specific fruit development-related genes in pear. Conclusions Our findings indicate that PbCYP78A6 plays a critical role in fruit formation and provide insights into controlling parthenocarpy.

A bifunctional heterogeneous catalyst was designed and synthesized, denoted DMEDA/IL–NH2-MIL-101. The structure and physical-chemical characterization of DMEDA/IL–NH2-MIL-101 and its precursors were characterized by SEM, N2 adsorption-desorption, XPS, FT-IR, PXRD, elemental analysis, and TGA techniques. The date showed that the two catalytic components of N, N-dimethylethylenediamine (DMEDA) and 1-butyl-3-methylimidazolium bromide (BmimBr) were chemically immobilized in NH2-MIL-101 nanocages. The amine of DMEDA was grafted onto carrier NH2-MIL-101 by N–Cr coordinate covalent bonds and the ionic liquid of BmimBr (IL (Br−)) was anchored in the NH2-MIL-101 nanocages by ‘ship-in-a-bottle’ method, in which the amidogen of NH2-MIL-101 condensed with N, N-carbonyldiimidazole (CDI) firstly, and then alkylated with 1-bromo butane. This novel heterogeneous catalyst with two different active sites can efficiently catalyze the synthesis of N-aryl oxazolidin-2-ones from carbon dioxide (CO2), epoxides, and anilines in one-pot under mild solvent-free conditions. It not only showed good stability and recoverability after five cycles but also exhibited shape selectivity for the substrate due to the synergic catalysis of amine, ionic liquid, and NH2-MIL-101. This novel bifunctional material is a promising solid catalyst for the green synthesis of N-aryl oxazolidin-2-ones.

Dwarfing is an important agronomic characteristic in fruit breeding. However, due to the lack of dwarf cultivars and dwarf stocks, the dwarfing mechanism is poorly understood in pears. In this research, we discovered that the dwarf hybrid seedlings of pear (Pyrus bretschneideri Rehd.), ‘Red Zaosu,’ exhibited a xylem-deficient dwarf phenotype. The expression level of PbXND1, a suppressor of xylem development, was markedly enhanced in dwarf hybrid seedlings and its overexpression in pear results in a xylem-deficient dwarf phenotype. To further dissect the mechanism of PbXND1, PbTCP4 was isolated as a PbXND1 interaction protein through the pear yeast library. Root transformation experiments showed that PbTCP4 promotes root xylem development. Dual-luciferase assays showed that PbXND1 interactions with PbTCP4 suppressed the function of PbTCP4. PbXND1 expression resulted in a small amount of PbTCP4 sequestration in the cytoplasm and thereby prevented it from activating the gene expression, as assessed by bimolecular fluorescence complementation and co-location analyses. Additionally, PbXND1 affected the DNA-binding ability of PbTCP4, as determined by utilizing an electrophoretic mobility shift assay. These results suggest that PbXND1 regulates the function of PbTCP4 principally by affecting the DNA-binding ability of PbTCP4, whereas the cytoplasmic sequestration of PbTCP4 is only a minor factor. Taken together, this study provides new theoretical support for the extreme dwarfism associated with the absence of xylem caused by PbXND1, and it has significant reference value for the breeding of dwarf varieties and dwarf rootstocks of the pear.

‘Yunnan’ quince (Cydonia oblonga Mill.) is used as the dwarfing rootstock for pear (Pyrus spp.). Here, we reported that the sugar contents in mature ‘Zaosu’ pear fruit grafted on ‘Yunan’ quince (Z/Q) were higher than that in ‘Zaosu’ pear fruit grafted on ‘Duli’ (Pyrus betulifolia) (Z/D). To investigate the underlying mechanism, the leaf photosynthetic capacity and the leaf-to-fruit assimilate transport capacity were initially analyzed. The leaf photosynthetic capacity was similar between Z/Q and Z/D, but the assimilate transport capacity was greater for Z/Q than for Z/D. Sugar transporters mediate the distribution of assimilates; therefore, changes in PbSWEET transcriptional patterns were examined. PbSWEET6 was highly expressed in Z/Q fruit. Thus, the PbSWEET6 function related to assimilate transport was further verified. Sucrose and glucose contents increased in transgenic tomato fruit and pear fruit calli overexpressing PbSWEET6. Taken together, these results suggest that ‘Yunnan’ quince positively regulated fruit sugar contents by influencing the flow of PbSWEET6-involved assimilates in the scion.

In the aero-optic turbulent boundary layer (TBL), there exist very rich air flow structures that fall into a wide range of scales, with the smallest being roughly of the order of the optical wavelength. However, these fine spatial variations cannot be neglected when one is dealing with light propagation through such structures, since both the amplitude and phase of a light wave undergo modulations. In this study, we studied the influence of TBL on the angular momentum spectrum of light and found that there exists critical point of the azimuthal distribution of the disturbance phase that determines the symmetric properties of the expansion spectrum.

Abstract Background As a class of natural antioxidants in plants, fruit flavonol metabolites are beneficial to human health. However, the regulatory networks for flavonol biosynthesis in most fruits are largely unknown. Previously, we reported a spontaneous pear bud sport ‘Red Zaosu’ (Pyrus bretschneideri Rehd.) with a high flavonoid content in its fruit. The identification of the flavonol biosynthetic regulatory network in this mutant pear fruit is crucial for elucidating the flavonol biosynthetic mechanism in fruit. Results Here, we demonstrated the PbMYB12b positively regulated flavonols biosynthesis in ‘Red Zaosu’ fruit. Initially, we investigated the accumulation patterns of four major quercetin glycosides and two major isorhamnetin glycosides in the fruit of ‘Red Zaosu’ and its wild-type ‘Zaosu’. A PRODUCTION OF FLAVONOL GLYCOSIDES (PFG)-type MYB transcription factor PbMYB12b was also screened for because of its correlation with flavonol accumulation in pear fruit. The biofunction of PbMYB12b was verified by transient overexpression and RNAi assays in pear fruit and young leaves. Overexpression of PbMYB12b enhanced the biosynthesis of quercetin glycosides and isorhamnetin glycosides by positively regulating a general flavonoids biosynthesis gene PbCHSb and a flavonol biosynthesis gene PbFLS. This finding was also supported by dual-luciferase transient expression assay and transient β-glucuronidase (GUS) reporter assay. Conclusions Our study indicated that PbMYB12b positively regulated flavonol biosynthesis, including four major quercetin glycosides and two major isorhamnetin glycosides, by promoting the expression of PbCHSb and PbFLS in pear fruit.

Fourier transform near-infrared (FT-NIR) spectroscopy is a nondestructive, rapid, real-time analysis of technical detection methods with an important reference value for producers and consumers. In this study, the feasibility of using FT-NIR spectroscopy for the rapid quantitative analysis and qualitative analysis of ‘Zaosu’ and ‘Dangshansuli’ pears is explored. The quantitative model was established by partial least squares (PLS) regression combined with cross-validation based on the spectral data of 340 pear fresh fruits and synchronized with the reference values determined by conventional assays. Furthermore, NIR spectroscopy combined with cluster analysis was used to identify varieties of ‘Zaosu’ and ‘Dangshansuli’. As a result, the model developed using FT-NIR spectroscopy gave the best results for the prediction models of soluble solid content (SSC) and titratable acidity (TA) of ‘Dangshansuli’ (residual prediction deviation, RPD: 3.272 and 2.239), which were better than those developed for ‘Zaosu’ SSC and TA modeling (RPD: 1.407 and 1.471). The results also showed that the variety identification of ‘Zaosu’ and ‘Dangshansuli’ could be carried out based on FT-NIR spectroscopy, and the discrimination accuracy was 100%. Overall, FT-NIR spectroscopy is a good tool for rapid and nondestructive analysis of the internal quality and variety identification of fresh pears.

Minimum miscible pressure (MMP) is an essential design parameter of gas flooding for enhanced oil recovery (EOR) applications. Researchers have developed a number of methods for MMP computations, including the analytical methods, the slim-tube simulation method, and the multiple-mixing-cell (MMC) method. Among these methods, the MMC method is widely accepted for its simplicity, robustness, and moderate computational cost An important version of the MMC method is the Jaubert et al. method which has a much lower computational cost than the slim-tube simulation method. However, the original Jaubert et al. method suffers several drawbacks. One notable drawback is that it cannot be applied to the scenario where the oil-gas MMP is lower than the saturation pressure of the crude oil. In this work, we present a modified MMC method that is more versatile and robust than the original version. Our method can handle the scenario where the oil-gas MMP is lower than the saturation pressure of the crude oil. Besides, we propose a modified MMC model that can reduce the computational cost of MMP estimations. This modified model, together with a newly proposed pressure search algorithm, increases the MMP estimation accuracy of the modified method. We demonstrate the good performance of the modified MMC method by testing it in multiple case studies. A good agreement is obtained between the MMPs calculated by the modified method and the tie-line-based ones from the literature.

Fruit set and development occur following successful fertilization. Parthenocarpy, a valuable trait in some self-incompatible species, produces seedless fruit without fertilization. Gibberellin (GA) is a crucial hormone in fruit-set regulation and development. While investigating the development of parthenocarpy in pear (Pyrus bretschneideri Rehd.), we determined that GA 20-oxidases (GA20ox) may play key roles in seedless pear fruit development. Sequence analysis revealed three PbGA20ox genes: PbGA20ox1, PbGA20ox2, and PbGA20ox3. We analyzed the expression patterns of candidate genes and found that PbGA20ox2 levels significantly changed in pollinated fruits. Tissue-specific expression assays revealed that PbGA20ox2 is highly expressed in young fruit and leaves. Subcellular localization assays showed it was located in the cytoplasm, nucleus, and plasma membrane. Overexpressed PbGA20ox2 tomato plants were taller and had longer hypocotyls and internodes, and the emasculated flowers produced parthenocarpic fruit. In pear, the transient overexpression of PbGA20ox2 promoted fruit development and delayed the drop of nonpollinated fruit. Furthermore, the fruit of PbGA20ox2-overexpressing tomato and transient PbGA20ox2-overexpressing pear had increased GA4 (but not GA3 and GA1) contents. This result provided evidence that PbGA20ox2 was necessary for GA4-dependent pear fruit development. Our study revealed that PbGA20ox2 altered the GA biosynthetic pathway and enhanced GA4 synthesis, thereby promoting fruit set and parthenocarpic fruit development.

The turbulent Rayleigh–Bénard (R–B) convection system contains the plume and the large-scale circulation structure, which causes the statistical inhomogeneity of the flow field. The high coherence of the laser leads to the completely different transmission characteristics in the R–B flow field than in the free space. In this study, the transient scattering field of the laser in the R–B flow field is calculated by using the Maxwell numerical integration method under the Rytov approximation. The experimental device was designed, the comparison experiment was carried out, and several satisfactory contrast results were given.

Asian pear: Plant hormones induce seedless fruit Various hormonal, anatomical and genetic changes explain how a plant hormone can induce pears to make seedless fruit without fertilization. Lingfei Xu and colleagues from Northwest A&F University in Yangling, China, studied the effect of plant growth hormones known as gibberellins on fruit development in the Dangshansuli pear, Pyrus bretschneideri Rehd. They found that spraying a mixture of two gibberellins, known as GA4+7, on unpollinated flowers produced seedless mature fruits of a normal size, whereas treatment with another gibberellin, GA3, yielded fruit that died before harvest. Analyses of gene expression, hormone levels and cell growth in the developing pear fruits showed that applying GA4+7 to unpollinated flowers generated many of the same effects as pollination. The findings could aid in future commercial production of this popular Asian fruit.

Seedless fruit is a feature appreciated by consumers. The ovule abortion process is highly orchestrated and controlled by numerous environmental and endogenous signals. However, the mechanisms underlying ovule abortion in pear remain obscure. Here, we found that gibberellins (GAs) have diverse functions during ovules development between seedless pear ‘1913’ and seeded pear, and that GA4+7 activates a potential programmed cell death process in ‘1913’ ovules. After hormone analyses, strong correlations were determined among jasmonic acid (JA), ethylene and salicylic acid (SA) in seedless and seeded cultivars, and GA4+7 treatments altered the hormone accumulation levels in ovules, resulting in significant correlations between GA and both JA and ethylene. Additionally, SA contributed to ovule abortion in ‘1913’. Exogenously supplying JA, SA or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid promoted ‘Bartlett’ seed death. The regulatory mechanism in which ethylene controls ovule death has been demonstrated; therefore, JA’s role in regulating ‘1913’ ovule abortion was investigated. A further study identified that the JA signaling receptor MYC2 bound the SENESCENCE-ASSOCIATED 39 promoter and triggered its expression to regulate ovule abortion. Thus, we established ovule abortion-related relationships between GA and the hormones JA, ethylene and SA, and we determined their synergistic functions in regulating ovule death.

The N-terminal of Myc-like basic helix-loop-helix transcription factors (bHLH TFs) contains an interaction domain, namely the MYB-interacting region (MIR), which interacts with the R2R3-MYB proteins to regulate genes involved in the anthocyanin biosynthetic pathway. However, the functions of MIR-domain bHLHs in this pathway are not fully understood. In this study, PbbHLH2 containing the MIR-domain was identified and its function investigated. The overexpression of PbbHLH2 in ”Zaosu” pear peel increased the anthocyanin content and the expression levels of late biosynthetic genes. Bimolecular fluorescence complementation showed that PbbHLH2 interacted with R2R3-MYB TFs PbMYB9, 10, and 10b in onion epidermal cells and confirmed that MIR-domain plays important roles in the interaction between the MIR-domain bHLH and R2R3-MYB TFs. Moreover, PbbHLH2 bound and activated the dihydroflavonol reductase promoter in yeast one-hybrid (Y1H) and dual-luciferase assays. Taken together these results suggested that the MIR domain of PbbHLH2 regulated anthocyanin biosynthesis in pear fruit peel.

The near infrared (NIR) laser drilling of a carbon fiber reinforced polymer (CFRP) composite in the continuous wave (CW) mode and the ms pulse mode was investigated by an experiment and a numerical simulation. The relationships between the laser penetrating time, entrance hole diameter, surface heat affected zone (HAZ) width, and material ablation rate and the laser irradiation time and laser peak power densities were obtained from the experiment. For the same average power density of the laser output, 3.5 kW/cm2, it was found that the ms pulse laser mode, which had a higher peak power density, had a higher drilling efficiency. When drilling the same holes, the pulse laser mode, which had the highest peak power density of 49.8 kW/cm2, had the lowest drilling time of 0.23 s and had the smallest surface HAZ width of 0.54 mm. In addition, it was found that the laser penetrating time decreased sharply when the peak power density was higher than 23.4 kW/cm2. After analyzing the internal gas pressure by the numerical simulation, it was considered that a large internal gas pressure appeared, which resulted from polymer pyrolysis, causing a large amount of the mechanical erosion of the composite material to improve the drilling efficiency. Therefore, the ms pulse laser showed its potential and advantage in laser drilling the CFRP composite.

Anthocyanin biosynthesis exhibits a rhythmic oscillation pattern in some plants. To investigate the correlation between the oscillatory regulatory network and anthocyanin biosynthesis in pear, the anthocyanin accumulation and the expression patterns of anthocyanin late biosynthetic genes (ALBGs) were investigated in fruit skin of ‘Red Zaosu’ (Pyrus bretschneideri Rehd.). The anthocyanin accumulated mainly during the night over three continuous days in the fruit skin, and the ALBGs’ expression patterns in ‘Red Zaosu’ fruit skin were oscillatory. However, the expression levels of typical anthocyanin-related transcription factors did not follow this pattern. Here, we found that the expression patterns of four PbREVEILLEs (PbRVEs), members of a class of atypical anthocyanin-regulated MYBs, were consistent with those of ALBGs in ‘Red Zaosu’ fruit skin over three continuous days. Additionally, transient expression assays indicated that the four PbRVEs promoted anthocyanin biosynthesis by regulating the expression of the anthocyanin biosynthetic genes encoding dihydroflavonol-4-reductase (DFR) and anthocyanidin synthase (ANS) in red pear fruit skin, which was verified using a dual-luciferase reporter assay. Moreover, a yeast one-hybrid assay indicated that PbRVE1a, 1b and 7 directly bound to PbDFR and PbANS promoters. Thus, PbRVEs promote anthocyanin accumulation at night by up-regulating the expression levels of PbDFR and PbANS in ‘Red Zaosu’ fruit skin.

Subgroup 4 R2R3 MYBs play vital roles in the regulation of anthocyanin biosynthesis. However, there is limited knowledge regarding the functions of MYB repressors in pear (Pyrus × bretschneideri). Here, PbMYB120 was identified as a potential regulator of anthocyanin biosynthesis. A phylogenetic analysis revealed that PbMYB120 was clustered into the FaMYB1-like clade of the subgroup 4 R2R3 MYBs. PbMYB120 was expressed higher in red peels than in green peels in five pear cultivars. PbMYB120 expression was positively correlated with anthocyanin accumulation. However, the transient overexpression of PbMYB120 led to the inhibition of anthocyanin accumulation and PbUFGT1 expression. Promoter binding and activation assays indicated that PbMYB120 binds to the promoter of PbUFGT1 and represses the promoter’s activity. Thus, the inhibition of anthocyanin accumulation by PbMYB120 may be correlated with the repression of PbUFGT1. Furthermore, during anthocyanin induction, the expression levels of anthocyanin activators and PbMYB120 were upregulated. This study demonstrated that PbMYB120 was highly expressed in pear tissues having higher anthocyanin accumulations but acted as a repressor in the regulation of anthocyanin accumulation. PbMYB120 may work coordinately with anthocyanin activators and serve as a balancer of anthocyanin accumulation.

Aroma affects the sensory quality of fruit and, consequently, consumer satisfaction. Melatonin (MT) is a plant growth regulator used to delay senescence in postharvest fruit during storage; however, its effect on aroma of pear fruit remains unclear. In this study, we assessed the effects of 0.1 mmol L−1 MT on volatiles and associated gene expression in the fruit of pear cultivars ‘Korla’ (Pyrus brestschneideri Rehd) and ‘Abbé Fetel’ (Pyrus communis L.). MT mainly affected the production of C6 aromatic substances in the two varieties. In ‘Korla’, MT inhibited expression of PbHPL, and reduced hydroperoxide lyase (HPL) activity and content of hexanal and (E)-hex-2-enal. In contrast, MT inhibited activity of lipoxygenase (LOX), reduced expression of PbLOX1 and PbLOX2, promoted PbAAT gene expression, increased alcohol acyltransferase (AAT) activity, and increased propyl acetate, and hexyl acetate content in ‘Abbé Fetel’ that similarly led to the reduction in content of hexanal and (E)-hex-2-enal. Content of esters in ‘Abbé Fetel’ pear increased with increasing postharvest storage period. Although mechanisms differed between the two varieties, effects on aroma volatiles mediated by MT were driven by expression of genes encoding LOX, HPL, and AAT enzymes.

Parthenocarpy, the production of seedless fruit without fertilization, has a variety of valuable qualities, especially for self-incompatible species, such as pear. To explore whether melatonin (MT) induces parthenocarpy, we used ‘Starkrimson’ pear as a material for morphological observations. According to our results, exogenous MT promoted the expansion and division of the mesocarp cells in a manner similar to hand pollination. However, the seeds of exogenous MT-treated fruit were undeveloped and aborted later in the fruit-setting stage. To further investigate how MT induced parthenocarpy, we studied changes of related hormones in the ovaries and found that MT significantly increased the contents of the gibberellins (GAs) GA3 and GA4. Thus, paclobutrazol (PAC), a GA-biosynthesis inhibitor, was used to study the relationship between GAs and MT. In addition, spraying MT after treatment with PAC did not increase GA content nor lead to parthenocarpy. Through a transcriptome analysis, we discovered that MT can cause significant upregulation of PbGA20ox and downregulation of PbGA2ox. However, no significant difference was observed in PbGA2ox compared with the control after PAC and MT applications. Thus, MT induces parthenocarpy by promoting GA biosynthesis along with cell division and mesocarp expansion in pear.

Differences in coloration exist among red pear cultivars. Here, we selected six red pear cultivars with different genetic backgrounds to elucidate the characteristics of fruit pigmentation. We detected anthocyanin contents and the expression levels of anthocyanin synthesis-related genes in these cultivars at different stages of fruit development. The anthocyanin contents of all six cultivars showed a rise–drop tendency. Principal component and hierarchical cluster analyses were used to distinguish the types of cultivars and the genes crucial to each anthocyanin accumulation pattern. The six cultivars were divided into three groups. Red Zaosu were clustered into one group, Red Sichou and Starkrimson into another group, and Palacer, Red Bartlett, and 5 Hao clustered into a third group. The expression levels of F3H, UFGT2, MYB10, and bHLH3 were similar among the differential coloration patterns of the six cultivars, suggesting a critical and coordinated mechanism for anthocyanin synthesis. Anthocyanin transporters (GST) and light-responsive genes, such as COP1, PIF3.1, and PIF3.2 played limited roles in the regulation of anthocyanin accumulation. This study provides novel insights into the regulation of anthocyanins synthesis and accumulation in red pears.

The synthesis of anthocyanin in pear (Pyrus bretschneideri) fruit is regulated by light. However, little is known about the molecular mechanisms of pear fruit coloring mediated by upstream light-signaling regulators. Here, the photoresponse factors CONSTITUTIVE PHOTOMORPHOGENIC (COP) 1.1 and 1.2 were cloned from ‘Red Zaosu’ peel to study their functions in pear fruit coloring. The overexpression vectors pBI121-PbCOP1.1 and pBI121-PbCOP1.2 were constructed to analyze their effects on anthocyanin synthesis in pear fruit. A protein sequence alignment and phylogenetic tree analysis revealed that PbCOP1 proteins are highly homologous with those of other species. An analysis of tissue differential expression showed that the greatest expression levels of PbCOP1s occurred in the leaves. Their expression levels increased in the leaves during development, when the leaves changed from red to green. The overexpression of PbCOP1s in the peel resulted in reduced anthocyanin synthesis at the injection sites. A quantitative PCR analysis of the injection sites showed that PbCOP1.1 significantly inhibited the expression of the anthocyanin synthesis-related genes CHI, DFR, UFGT2, bHLH3, HY5 and GST. Based on the above results, we hypothesize that PbCOP1.1 is an anthocyanin synthetic inhibitory factor of pear coloration.