Pyrus Bretschneideri Research Articles

The role of sucrose-metabolizing enzymes in pear fruit that differ in sucrose accumulation

In the paper, the soluble sugar composition and activities of enzymes metabolizing sucrose: invertase (β-fructosidase, EC 3.2.1.26), sucrose synthase (SS; EC 2.4.1.13) and sucrose-phosphate synthase (SPS; EC 2.4.1.14) were investigated during fruit development of two pear species: Pyrus bretschneideri Rehd. cv. ‘Yali’ and P. pyrifolia Nakai cv. ‘Aikansui’, characterized as low and high sucrose types, respectively. It was found that, at the end of fruit development of ‘Aikansui’, the level of sucrose was five times higher than in ‘Yali’ in the same period. It was coincident with the significantly higher activities of SS (synthesis) and SPS and lower activities of invertase (vacuolar and cell wall-bound acid invertase and neutral invertase). The high correlation was found between sucrose level and SS (synthesis) and SPS activities in ‘Aikansui’ pears.

Molecular cloning and expression analysis of a gene for sucrose transporter from pear (Pyrus bretschneideri Rehd.) fruit

Here we report the cloning of a sucrose transporter cDNA from pear (Pyrus bretschneideri Rehd. cv ‘Yali’) fruit and an analysis of the expression of the gene. A cDNA clone, designated PbSUT1 was identified as a sucrose transporter cDNA from its sequence homology at the amino acid level to sucrose transporters that have been cloned from other higher plant species. PbSUT1 potentially encoded a protein of 499 amino acid residues with a predicted molecular mass of 53.4 kDa and an isoelectric point (pI) of 9.21. Phylogenetic analysis revealed that the PbSUT1 belonged to type III SUTs and was more closely related to the MdSUT1 from apple fruit. Some major facilitator superfamily (MFS)-specific sequence motifs were found in the predicted PbSUT1 peptides, and an MFS_1 domain was located at the amino acid positions of 29–447 of the sequence. A study of gene expression along fruit development showed that PbSUT1 transcripts are present at all stages but significantly increase before fruit enlargement and during the ripening process with increasing sucrose levels. In contrast, the expression levels don't change much during the period of rapid fruit growth. This work shows that sucrose transporter may play a role in the accumulation of sugars during maturation and in maintaining the internal cellular distribution.

Characteristics of the water–energy–carbon fluxes of irrigated pear (Pyrus bretschneideri Rehd) orchards in the North China Plain

Pear trees (Pyrus bretschneideri Rehd) play an important role in the fruit production in the North China Plain (NCP) where water shortage is a serious problem. The objectives of this research were to explore the characteristics of water balance, energy transfer and carbon exchange of irrigated pear orchards by a combination of multiple measurement methods (eddy covariance system, sap flow method, and the other equipment). Experiments from 08/01/2011 to 10/31/2012 were conducted in a pear orchard located in the NCP. Annual net radiation (Rn) was 2490MJm−2 of which latent heat flux accounted for 74.5%, a little higher than the agro-ecosystem with wheat–maize rotation (70%). Annual mean water use efficient (WUE) was 1.98gCO2/kgH2O which was lower than the agro-ecosystem in the same area. Annual evapotranspiration (ET) was 759mm and daily transpiration (T) ranged from 0.5 to 4.3mm during May to October while daily T/ET varied from 0.6 to 0.9. Variation of ET can be explained well by the change of LAI. As annual drainage was 86mm, it will take a long time for the shallow soil water (0–140cm) to replenish deep groundwater. Optimal values of daily downward short wave radiation (Rs) (20MJm−2d−1) and ET (∼4.8mmd−1) were probably important thresholds for the plant growth. Changing irrigation method and crops planting structure adjusting according to the water balance and trees growth characteristics, were probably useful for keeping high yield with less water depletion while further research should be done in future.

First Report of Colletotrichum fructicola Causing Bitter Rot of Pear (Pyrus bretschneideri) in China.

Pyrus bretschneideri cv. Dangshansuli is the most important commercial Asiatic pear cultivar worldwide. In recent years, a fruit rot disease of unknown etiology have caused considerable fresh market losses in the 'Dangshansuli' production operations in Dangshan county, Anhui Province, China. Fresh market losses typically range from 60 to 90% and in 2008 were estimated at US$150 million. Symptomatic mature 'Dangshansuli' pears were collected from an orchard in Dangshan County in February 2008. A thin section (about 1 mm3) of symptomatic tissue was sterilized in a bleach and placed on potato dextrose agar (PDA) medium for isolation. From all fruit, a single fungus was recovered displaying gray-white dense aerial mycelium. Identical fungi were isolated from six additional symptomatic 'Dangshansuli' pears collected from other orchards in the county. Pathogenicity tests using one isolate (DS-0) were conducted in triplicate by placing 4 mm diameter discs from 7-day-old PDA plates onto the mature 'Dangshansuli' pear fruit that were incubated in an incubator at 25°C with a 12-h photoperiod for 30 days. An equal number of noncolonized PDA inoculations were included as a control. Isolate DS-0 caused symptoms similar to those in the field within 7 days and complete collapse of cortical tissues within 30 days. No symptoms were observed on control fruit. Round brownish lesions with a diameter of about 3 cm on inoculated fruit was populated by sunken, rotiform acervuli on which numerous, colorless, oblong single cell shape conidia with width/length of 6 × 20 μm were produced. A comparison of morphology and sequence analysis of the ribosomal internal transcribed spacer (ITS) regions in pre- and post-inoculation cultures from inoculated fruit confirmed the presence DS-0. To further characterize DS-0, aliquots of extracted genomic DNA from the fungus were subjected to PCR amplification and sequencing of seven gene regions from the ITS, actin (ACT), β-tubulin 2 (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), manganese-superoxide dismutase (SOD2), chitin synthase (CHS-1), and calmodulin (CAL), using the primers listed by Weir et al (4), except for the primer pair of ITS1 (5'-TCCGTAGGTGAACCTGCGG-3') and ITS4 (5'-TCCTCCGCTTATTGATATGC-3') for ITS amplification, and SODglo2-R (5'-TAGTACGCGTGCTCGGACAT-3') and SODglo2-R (5'-TAGTACGCGTGCTCGGACAT-3') for TBU2 amplification. Two or three clones of PCR products of each gene were sequenced and compared (GenBank Accession Nos. KC410780 to KC410786) to published data at http://www.cbs.knaw.nl/colletotrichum . The result indicated that DS-0 shared the highest similarity of 99.91% with Colletotrichum fructicola, corroborating numerous reports of Colletotrichum spp. causing bitter rot of pear on P. pyrifolia (1,2,3,4). C. fructicola was only recently reported as causing bitter rot of P. pyrifolia (4) and to our knowledge, this is the first report of C. fructicola causing bitter rot of P. bretschneideri, which will help producers select the best management practices for this devastating disease.

Maturity and cooling rate affects browning, polyphenol oxidase activity and gene expression of ‘Yali’ pears during storage

Browning is the main physiological disorder of ‘Yali’ pear (Pyrus bretschneideri Rehd) during storage. In this study, the relationships between browning development in fruit from different harvest dates, and cooled either rapidly or slowly, with polyphenol oxidase (PPO) activity and isozymes, and PPO gene expression has been investigated. Development of browning was highest in late-harvest fruit in both core and flesh tissues and was higher in rapidly cooled than slowly cooled fruit. Mid-harvest fruit had the lowest browning incidence and PPO activity of core tissue was higher than in flesh and seeds, while the peak of PPO activity in mid-harvest fruit was the lowest. Six PPO isoenzymes were detected in fruit, three bands A, B and E in flesh and core tissues, three bands C, D and F in the seeds. The intensity of PPO isoenzyme staining of bands A and B in pulp and core was similar to that of PPO activity and browning incidence. PPO gene expression increased and then decreased in core tissues. Trends of expression were similar to those of PPO activity. Rapid cooling promoted the expression PPO. The results suggest PPO plays an important role in ‘Yali’ pear browning during storage.

Structural characterization and deposition of stone cell lignin in Dangshan Su pear

Stone cell content is one determinant of pear fruit quality. Stone cells are formed by the deposition of lignin on primary cell walls, followed by the secondary thickening of cell walls. Studies of the structural features and deposition of pear lignin were rare. To understand the structural characteristics of pear fruit lignin, chemical functional groups and bond types of pear fruit lignin were studied, along with an analysis of the deposition of lignin in the stone cell. Lignin was extracted, purified and analyzed by Fourier-transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The deposition of lignin in the pear stone cell wall was detected by electron microscopy. Lignin in the pulp of Pyrus bretschneideri cv. Dangshan Su pear comprised guaiacyl-syringyl-lignin, with a relatively high amount of guaiacyl-lignin (G) compared to syringyl lignin (S). During the early development of Dangshan Su pear, lignin exhibited CO stretching in unconjugated ketoses, carbonyls and esters, but during later development, aliphatic CH stretching in CH3 (not in Ome) and phen OH occurred. The main linkages of the acetylated milled wood lignin structural units in Dangshan Su pear fruit are β-O-4, β-1, β-5 and β-β. β-O-4 was the major factor related to the solubility of lignin, with the presence of few β-5 linkages corresponding to the formation of fewer condensation-type structures, while the presence of fewer than 30% phenolic hydroxyl groups suggested that this lignin exhibited low levels of polymerization. In addition, a large number of hydrocarbon protons and side chains were present in Dangshan Su pear fruit lignin, suggesting this lignin is more easily dissolved than those with more condensation-type structures. Dangshan Su pear fruit lignin exhibited low levels of polymerization and was therefore easily hydrolyzed. Ultramicroscopy revealed that lignification extended from the corner of the primary cell wall to the remaining regions of the compound N middle lamella and the secondary wall, with lignin particles deposited along the cellulose microfibrils. Lignin particles and microfibrils were alternatively arranged until they filled up the entire cell cavity, culminating in the formation of stone cells.

Identification of a canonical SCFSLF complex involved in S-RNase-based self-incompatibility of Pyrus (Rosaceae)

S-RNase-based self-incompatibility (SI) is an intraspecific reproductive barrier to prevent self-fertilization found in many species of the Solanaceae, Plantaginaceae and Rosaceae. In this system, S-RNase and SLF/SFB (S-locus F-box) genes have been shown to control the pistil and pollen SI specificity, respectively. Recent studies have shown that the SLF functions as a substrate receptor of a SCF (Skp1/Cullin1/F-box)-type E3 ubiquitin ligase complex to target S-RNases in Solanaceae and Plantaginaceae, but its role in Rosaceae remains largely undefined. Here we report the identification of two pollen-specific SLF-interacting Skp1-like (SSK) proteins, PbSSK1 and PbSSK2, in Pyrus bretschneideri from the tribe Pyreae of Rosaceae. Both yeast two-hybrid and pull-down assays demonstrated that they could connect PbSLFs to PbCUL1 to form a putative canonical SCF(SLF) (SSK/CUL1/SLF) complex in Pyrus. Furthermore, pull-down assays showed that the SSK proteins could bind SLF and CUL1 in a cross-species manner between Pyrus and Petunia. Additionally, phylogenetic analysis revealed that the SSK-like proteins from Solanaceae, Plantaginaceae and Rosaceae form a monoclade group, hinting their shared evolutionary origin. Taken together, with the recent identification of a canonical SCF(SFB) complex in Prunus of the tribe Amygdaleae of Rosaceae, our results show that a conserved canonical SCF(SLF/SFB) complex is present in Solanaceae, Plantaginaceae and Rosaceae, implying that S-RNase-based self-incompatibility shares a similar molecular and biochemical mechanism.

Changes in physiology and quality of Laiyang pear in long time storage

Physiological disorders easily occur in Laiyang pear (Pyrus bretschneideri cv. Laiyang) fruit after harvest and result in quality deterioration and short postharvest life. In this paper, we mainly investigated the effects of 1-methylcyclopropene (1-MCP) treatment and controlled atmosphere (CA) with 2% O2 plus 2% CO2 on quality of Laiyang pear and storage time. The results indicated that 1-MCP treatment and CA were effective in maintaining quality and prolonging storage time of Laiyang pear fruit, because 1-MCP and CA could significantly delay fruit senescence via limiting ethylene production, reducing fruit respiration rate, regulating anti-oxidant enzymes and membrane permeability. We consider that the major action modes of 1-MCP and CA, that can maintain harvested quality of Laiyang pear fruit, may be greatly contributed to inhibiting ethylene biosynthesis and regulating anti-oxidant pathways.

The genome of the pear (Pyrus bretschneideri Rehd.)

The draft genome of the pear (Pyrus bretschneideri) using a combination of BAC-by-BAC and next-generation sequencing is reported. A 512.0-Mb sequence corresponding to 97.1% of the estimated genome size of this highly heterozygous species is assembled with 194× coverage. High-density genetic maps comprising 2005 SNP markers anchored 75.5% of the sequence to all 17 chromosomes. The pear genome encodes 42,812 protein-coding genes, and of these, ∼28.5% encode multiple isoforms. Repetitive sequences of 271.9 Mb in length, accounting for 53.1% of the pear genome, are identified. Simulation of eudicots to the ancestor of Rosaceae has reconstructed nine ancestral chromosomes. Pear and apple diverged from each other ∼5.4–21.5 million years ago, and a recent whole-genome duplication (WGD) event must have occurred 30–45 MYA prior to their divergence, but following divergence from strawberry. When compared with the apple genome sequence, size differences between the apple and pear genomes are confirmed mainly due to the presence of repetitive sequences predominantly contributed by transposable elements (TEs), while genic regions are similar in both species. Genes critical for self-incompatibility, lignified stone cells (a unique feature of pear fruit), sorbitol metabolism, and volatile compounds of fruit have also been identified. Multiple candidate SFB genes appear as tandem repeats in the S-locus region of pear; while lignin synthesis-related gene family expansion and highly expressed gene families of HCT, C3′H, and CCOMT contribute to high accumulation of both G-lignin and S-lignin. Moreover, alpha-linolenic acid metabolism is a key pathway for aroma in pear fruit.

Transport of mRNA molecules coding NAC domain protein in grafted pear and transgenic tobacco

Grafting is an important cultivation method and recent research on the mechanism of interactions between rootstock nad scion is focused on the long-distance transport of mRNA and small RNAs in the phloem. Among these transportable molecules, NACP gene coding NAM, ATAF1/2, CUC2 (NAC) domain protein might be involved in apical meristem development. Here, we report the transport of NACP mRNA between Chinese pear (Pyrus bretschneideri) cv. Yali (scion) and the wild Pyrus betulaefolia Bunge (rootstock). Our results indicated that NACP mRNA can be transported in both directions from the 3rd to 10th day after micro-grafting. It can also be transported to the shoot apex 30 to 70 cm away from graft-union in 2-year-old grafted trees. For further investigation, transgenic tobaccos with 35S: P. betulaefolia-NACP construct were grafted on wild-type tobaccos (Nicotiana tabacum L. cv. Samsun). The sustainable transport of Pyrus-NACP mRNA through the graft-union occurred from the 15th day after grafting.

Analyses of early rough bark phenotype found in seedlings of a cross between the European pear ‘Bartlett’ and the Chinese pear ‘Yali’

One of the morphological symptoms of old age in trees is the development of rough bark on trunks and branches. Here we characterized pear seedlings with a unique phenotype, early rough bark (ERB). Eight-year-old normal and ERB seedlings from a cross between the European pear (Pyrus communis) cultivar ‘Bartlett’ and the Chinese pear (Pyrus bretschneideri) cultivar ‘Yali’ were used for morphological analyses and the determination of carbohydrates and lignin. Many rough surface patches were observed on the stems of 2-year-old ERB shoots, and most stem surfaces were covered by rough bark in 3-year-old ERB shoots while most stem surfaces were smooth in 2- and 3-year-old normal shoots. ERB plants also displayed rough-barked trunks, and the trunk surface was relatively smooth in normal plants. The content of lignin, one of the major components of cork tissues, was higher in ERB plants than in normal plants. The levels of starch and sucrose, which play roles in storage and translocation of carbon, were higher in ERB plants than that in normal plants, suggesting that the rate of carbon use is low in ERB plants. The novel phenotype ERB may enable future research on the formation of rough bark in fruit trees.

Proteomic analysis of ‘Zaosu’ pear (Pyrus bretschneideri Rehd.) and its red skin bud mutation

BackgroundBreeding for strong red skin color is an important objective of the pear breeding program. There are few reports of proteome research in green skin pear and its red skin bud mutation. The manuscript at hand is one of the first studies dealing with 2D-PAGE-based analysis of pear fruits and leaves, establishing a suitable sample preparation and testing different 2D-PAGE protocols. Therefore, it may grant a basis for further studies on the pear proteome being the studies main goal. A proteomic analysis was conducted on leaves and fruits of ‘Zaosu’ pear (Pyrus bretschneideri Rehd.) and its red skin bud mutation in order to reveal their genetic differences in the protein level.ResultsIn the present study, the optimized two-dimensional (2-D) gel electrophoresis system of pear leaf and fruit was set up, and applied to analyze the leaves and fruit protein. The interesting peptide fragments were determined using 4800 Plus MALDI TOF/TOFTM Analyzer mass spectrometer, and the sequence obtained was blasted in NCBInr to identify the differentially-expressed protein. In the 1.5-fold differently-expressed proteins between ‘Zaosu’ pear and its mutant, 10 out of 35 proteins in fruit and 12 out of 24 ones in leaves were identified successfully. Among the 22 identified proteins, 7 protein spots were related to photosynthesis and energy metabolism; 4 were associated with environmental stress; 4 with disease defense; 2 with amino acid metabolism; 2 with cytoskeleton; 1 with antioxidant function; 1 with calcium metabolism; and 1 with unknown function. Moreover, related physiological index, such as chlorophyll content, Rubisco content and polyphone oxidase activity, were different between ‘Zaosu’ pear and its mutant.ConclusionA 2-D gel electrophoresis system of pear leaves and fruits was established, which was suitable for the analysis of proteome comparison. To the best of our knowledge, we have performed the first analysis of the proteomic changes in leaves and fruits of ‘Zaosu’ pear and its red skin bud mutation. Our study provides important information on the use of proteomic methods for studying protein regulation of ‘Zaosu’ pear and its red skin bud mutation.

A phylogenetic network of wild Ussurian pears (Pyrus ussuriensis Maxim.) in China revealed by hypervariable regions of chloroplast DNA

In order to understand the genetic diversity of wild Ussurian pears in China, chloroplast DNA (cpDNA) of 186 wild accessions from 12 populations in Inner Mongolia, Heilongjiang and Jilin Provinces and 51 Chinese and European pear cultivars including Pyrus ussuriensis, Pyrus pyrifolia, Pyrus bretschneideri, Pyrus sinkiangensis and Pyruscommunis were investigated. Each accession was classified into one of three types (types A, B and C) based on two large deletions in the hypervariable regions between the accD–psaI and rps16–trnQ genes. Thirty haplotypes were identified by 32 mutations including 17 gaps (in/dels) and 15 base changes. Haplotype network analysis revealed that wild Chinese Ussurian pears could be grouped into subgroup I of type A. A haplotype, Hcp3, in subgroup I detected in Heilongjiang and Jilin Provinces was considered to be a divergent centre in Chinese Ussurian pears. However, the genetic diversity of wild accessions revealed by the two hypervariable regions was quite low. In particular, 98 % of wild Ussurian accessions in Inner Mongolia shared an identical haplotype Hcp1 and are, therefore, monomorphic. In comparison, Chinese pear cultivars were more divergent. These results suggest that the cpDNAs from wild Ussurian pears in Inner Mongolia have specifically differentiated compared to those from pears of other areas. The number of wild Ussurian pears has been decreasing because of desertification and land development, therefore conservation is needed.

Genetic structure of East Asian cultivated pears (Pyrus spp.) and their reclassification in accordance with the nomenclature of cultivated plants

By use of Bayesian statistical inference and allelic data for 18 microsatellite loci, we analyzed the genetic structure of Chinese, Korean, and Japanese pear cultivars and of native populations of Pyrus ussuriensis. Although Japanese pear cultivars had a simple genetic structure, Chinese and Korean pear cultivars were admixures of Japanese pear and native P. ussuriensis from the Asian continent. Genetic differentiation between groups of native populations and those of cultivars was high, but cultivars were not well differentiated from each other. Chinese and Korean cultivars, which have traditionally been classified as either P. ussuriensis, P. bretschneideri, or P. pyrifolia, were much closer to Japanese cultivars, which have traditionally been classified as P. pyrifolia, than to native P. ussuriensis. We propose a new classification of cultivars by using the Group concept in accordance with the International Nomenclature for Cultivated Plants, namely, the Pyrus Ussurian pear group, the Pyrus Chinese white pear group, the Pyrus Chinese sand pear group, and the Pyrus Japanese pear group.

Study on chemical composition, anti-inflammatory and anti-microbial activities of extracts from Chinese pear fruit (Pyrus bretschneideri Rehd.)

Pyrus bretschneideri Rehd. belongs to the genus Pyrus, a member of Rosaceae family. It is a routine edible fruit, and also used as a folk medicine to treat cough, eliminate constipation, and relieve alcoholism. In order to clarify the active compounds of P. bretschneideri, the phytochemical study were performed. Five compounds were isolated and identified as 2β,19α-dihydroxy ursolic acid, quercitrin, dibutyl phthalate, diisobutyl phthalate and α-amyrin. Additionally, we investigate the anti-inflammatory and anti-microbial effects of the fractions of P. bretschneideri partitioned with petroleum ether, ethyl acetate and n-butanol, respectively. In the carrageenan-induced rat paw edema test, the EtOAc fraction showed the strongest inhibition of edema formation 0.5–5h after edema induction, followed by n-butanol. EtOAc also displayed potent anti-inflammatory activity against xylene-induced ear edema (22.03% and 43.69%, respectively) and acetic acid-induced extravasation of Evan’s blue dye (39.58% and 49.92%, respectively) at the dose of 200 and 400mg/kg. While, the anti-microbial results showed that ethyl acetate and n-butanol fractions exhibited strong activity against the bacteria strains. Moreover, 2β,19α-dihydroxy ursolic acid, α-amyrin and quercitrin could significantly inhibit the ear edema induced by xylene at the dose of 20mg/kg, and exhibited moderate anti-microbial activities against the bacteria strains.

Cloning, characterization and promoter analysis of S-RNase gene promoter from Chinese pear (Pyrus pyrifolia)

The 5′‐flanking region of the S12-, S13-, S21-RNase with a length of 854bp, 1448bp and 1137bp were successfully isolated by TAIL-PCR from genomic DNA from ‘Jinhua’, ‘Maogong’ (Pyrus pyrifolia) and ‘Yali’ (Pyrus bretschneideri) genomic DNA. Sequence alignment and analysis of S13-, S12-, S21-RNase gene promoter sequences with S2-, S3-, S4-, S5-RNase 5′-flanking sequences indicated that a homology region of about 240bp exists in the regions just upstream of the putative TATA boxes of the seven Chinese/Japanese pear S-RNase genes. Phylogenetic tree suggests that the homology region between the Chinese/Japanese pear and apple S-RNase gene promoter regions reflects the divergence of S-RNase gene was formed before the differentiation of subfamilies. Full length and a series of 5′-deletion fragments-GUS fusions were constructed and introduced into Arabidopsis thaliana plants. GUS activity were detected in S12-pro-(1 to 5)-GUS‐pBll01.2 transgenic pistils and progressively decreased from S12-pro-1-GUS-pBI l01.2 to S12-pro-5-GUS-pBll01.2. No GUS activity was detected in S12-pro-6-GUS-pBll01.2 transgenic pistil and other tissues of non-transformants and all transgenic plants. The result suggested S12-RNase promoter is pistil specific expression promoter.

A suppression subtractive hybridization library construction for red skin mutant of ‘Zaosu’ pear and MYBR gene analysis

Red pear breeding is one of the major domestic and international pear breeding projects. The aim of this study is to investigate red skin development-related genes of the red skin mutant of ‘Zaosu’ (Pyrus bretschneideri Rehd.) pear and provide important information for elucidating the molecular mechanism of red pigment formation in the skin. A cDNA library was constructed using the suppression subtractive hybridization (SSH) method, in which the green-skinned pear ‘Zaosu’ served as the driver, and its red skin mutant ‘Zaosu Red’ served as the tester. All positive clones between 250–1000 bp were chosen and sequenced from the library, and 735 expressed sequence tags (ESTs) were obtained. According to BLAST screening and functional annotation in the GenBank database, 314 unique gene fragments were obtained. Among the obtained fragments, 198 ESTs were found to have homologous genes with known functions, 61 ESTs with unknown functions and 55 ESTs with no homologous genes. Results showed that the differentially expressed genes are involved in anthocyanin biosynthesis, signal transduction, energy metabolism, transcription, disease resistance and bud mutation. Moreover, a novel cDNA of ‘Zaosu Red’ MYBR gene was isolated with the strategy of in silico cloning in combination with RT-PCR from ‘Zaosu Red’ pear fruit. The full-length of MYBR cDNA was 1552 bp, with an open reading frame from 12 to 1355 bp, coded 447 amino acids.

Effects of 1-MCP on chlorophyll degradation pathway-associated genes expression and chloroplast ultrastructure during the peel yellowing of Chinese pear fruits in storage

The peel yellowing is an important pigment physiological process of green fruit ripening, which mainly results from chlorophyll degradation in the fruit peel. In this work, two typical cultivars with different ripening speed, a slow ripening pear ‘Emerald’ (Pyrus bretschneideri Rehd. cv. Emerald) and a fast ripening ‘Jingbai’ (Pyrus ussuriensis Maxim. cv. Jingbai) were used to investigate the molecular mechanism of chlorophyll degradation in pear yellowing/ripening during postharvest storage. The fruits after harvest were treated with 1-methylcyclopropene (1-MCP), an ethylene action inhibitor at 1.0μLl−1 to determine its effect on chloroplast ultrastructure and the expression of chlorophyll degradation associated genes in peel tissues. Our results show that the pears treated with 1-MCP had a lower ethylene production rate and higher chlorophyll content compared to those of untreated fruit. The more intact chloroplasts with well-organised grana thylakoids and small plastoglobuli were maintained in the peel of 1-MCP treated fruit for up to 30 and 15d in ‘Emerald’ and ‘Jingbai’, respectively. The expression of chlorophyll degradation associated genes: pheophorbide a oxygenase (PAO), non-yellow colouring (NYC), NYC1-like (NOL), stay-green 1(SGR1), was suppressed, while no significant change was found in chlorophyllase 1 (CHL1) and red chlorophyll catabolite reductase (RCCR) in both cultivar fruits treated with 1-MCP. These results suggest that 1-MCP can delay chlorophyll degradation by inhibiting ethylene production and suppressing the gene expression of PAO, NYC, NOL and SGR1, which are closely associated with chlorophyll catabolic pathway.

Preventing the wound-induced deterioration of Yali pears by chitosan coating treatments

Yali pears (Pyrus bretschneideri Rehd.) are susceptible to mechanical damage. In this study, the protective effects of chitosan treatments on the quality of bruised pears were evaluated. The fruit were treated with 1.5% chitosan before or after bruise damage, respectively. Then, the fruit were stored at 16 °C and 85-90% relative humidity. Postharvest quality parameters were analyzed during the storage. Bruise damage accelerated the decrease of firmness and the ratio of sugar to acid, while a delay of firmness and sugar-to-acid ratio in those pears treated with chitosan before or after was found. Meanwhile, chitosan treatments both before and after damage delayed the color changes caused by damage, inhibited disease incidence increase, and enhanced the bruise recovery during the storage. Our results suggested that chitosan treatment could be used to control the physiological responses induced by bruise damage.

Genetic Diversity of Some Pear Cultivars and Genotypes Using Simple Sequence Repeat (SSR) Markers

The genetic diversity and relationships among 47 pear cultivars and genotypes (Pyrus spp.), including 4 Japanese pears (Pyrus pyrifolia), 40 European pears (Pyrus communis), 1 Chinese pear (Pyrus bretschneideri) as well as 2 wild relatives (Pyrus salicifolia and Pyrus mazandaranica) were studied using 28 microsatellite primer pairs. A total of 174 alleles were produced at the 28 SSR loci with their sizes ranging from 81 to 290 bp. The number of observed alleles for each locus ranged from 3 (TsuENH014 and TsuENH046) to 12 (NB103a), with an average of 6.21 alleles per locus. In some SSR loci, more than two alleles were amplified in some cultivars and genotypes, suggesting that duplication has occurred in those accessions. This information suggests that at least two genomic regions exist for these loci in the pear genome. The observed heterozygosity (H o) values of amplified loci ranged from 0.17 (TsuENH006) to 0.97 (NB103a). Shannon's information index (I) value was observed to be highest (2.14) in the NB103a locus, while the TsuENH006 locus had the lowest value with an average of 1.37 among SSR loci. The Dice genetic similarity coefficient ranged from 0.29 (“Nijisseiki” and P. mazandaranica) to 0.91 (“Chojuro” and “Nijisseiki”) among samples. UPGMA cluster analysis showed two major groups corresponding to the Japanese and European pears.