Pyrus Bretschneideri Research Articles

PbCOL8 is a clock-regulated flowering time repressor in pear

The floral transition is controlled by diverse endogenous and exogenous cues. In many species, COL (CONSTANS-like) genes integrate light and circadian clock signals to regulate flowering time. However, little is known about COLs in perennial woody plants. Here, we identified 15 PbCOLs in pear (Pyrus bretschneideri). PbCOLs were classified into three groups by phylogenetic tree analysis using protein sequences. Multiple sequence alignment analysis revealed conserved B-box and CCT (CO, CO-like, and TOC1) domains in all PbCOL members. This result suggested that PbCOLs might possess conserved functions as other species. Six PbCOLs were found to be regulated by both circadian clock and photoperiod. Here, we showed that PbCOL8, a member of group 2, suppressed the flowering signal integrators FT and SOC1 and could repress flowering time. These findings will contribute to elucidation of the mechanism of floral initiation in pear.

B-BOX genes: genome-wide identification, evolution and their contribution to pollen growth in pear (Pyrus bretschneideri Rehd.)

BackgroundThe B-BOX (BBX) proteins have important functions in regulating plant growth and development. In plants, the BBX gene family has been identified in several plants, such as rice, Arabidopsis and tomato. However, there still lack a genome-wide survey of BBX genes in pear.ResultsIn the present study, a total of 25 BBX genes were identified in pear (Pyrus bretschneideri Rehd.). Subsequently, phylogenetic relationship, gene structure, gene duplication, transcriptome data and qRT-PCR were conducted on these BBX gene members. The transcript analysis revealed that twelve PbBBX genes (48%) were specifically expressed in pear pollen tubes. Furthermore, qRT-PCR analysis indicated that both PbBBX4 and PbBBX13 have potential role in pear fruit development, while PbBBX5 should be involved in the senescence of pear pollen tube.ConclusionsThis study provided a genome-wide survey of BBX gene family in pear, and highlighted its roles in both pear fruits and pollen tubes. The results will be useful in improving our understanding of the complexity of BBX gene family and functional characteristics of its members in future study.

In silico and expression analysis of the tonoplast monosaccharide transporter (TMT) gene family in Pyrus bretschneideri

ABSTRACTIn this study, we reported the identification, structural characteristics, phylogenetic, and expression patterns of 6 TMT genes (PbTMT1 to PbTMT6) in Pyrus bretschneideri. The 6 PbTMT genes were located on chromosomes 6, 5, 5, 10, 15, and 15, respectively. Analysis of the exons/introns revealed that all 6 genes contain the same exons and display a high degree of conservation with corresponding TMT genes in other plant species. Comparative screening of the motifs in PbTMT proteins indicated high conservation in terms of number, width, and order of motifs, which indirectly indicated that the 6 PbTMT proteins are indeed members of the TMT gene family. Phylogenetic analysis revealed that PbTMTs exhibited the greatest homology with those of Malus domestica. Analysis of expression levels of the 6 PbTMT genes revealed that transcripts of PbTMT5 were nearly undetectable in seeds but were highly expressed in stems and flowers. The other PbTMTs were differentially expressed in all tissues. PbTMT1 exhibited relatively uniform expression in various tissues, whereas PbTMT2, PbTMT3 and PbTMT6 were highly expressed in mature leaves. PbTMT4 was highly expressed in mature fruits, possibly indicating a key role in fruit sugar accumulation. These results would be useful in the selection of important candidate PbTMTs.

Genome-wide identification of the MADS-box transcription factor family in pear (Pyrus bretschneideri) reveals evolution and functional divergence.

MADS-box transcription factors play significant roles in plant developmental processes such as floral organ conformation, flowering time, and fruit development. Pear (Pyrus), as the third-most crucial temperate fruit crop, has been fully sequenced. However, there is limited information about the MADS family and its functional divergence in pear. In this study, a total of 95 MADS-box genes were identified in the pear genome, and classified into two types by phylogenetic analysis. Type I MADS-box genes were divided into three subfamilies and type II genes into 14 subfamilies. Synteny analysis suggested that whole-genome duplications have played key roles in the expansion of the MADS family, followed by rearrangement events. Purifying selection was the primary force driving MADS-box gene evolution in pear, and one gene pairs presented three codon sites under positive selection. Full-scale expression information for PbrMADS genes in vegetative and reproductive organs was provided and proved by transcriptional and reverse transcription PCR analysis. Furthermore, the PbrMADS11(12) gene, together with partners PbMYB10 and PbbHLH3 was confirmed to activate the promoters of the structural genes in anthocyanin pathway of red pear through dual luciferase assay. In addition, the PbrMADS11 and PbrMADS12 were deduced involving in the regulation of anthocyanin synthesis response to light and temperature changes. These results provide a solid foundation for future functional analysis of PbrMADS genes in different biological processes, especially of pigmentation in pear.

Deletion of Cu/Zn Superoxide Dismutase Gene sodC Reduces Aspergillus niger Virulence on Chinese White Pear

Aspergillus niger is a common pathogenic fungus causing postharvest rot of fruit and vegetable, whereas the knowledge on virulence factors is very limited. Superoxide dismutase [SOD (EC 1.15.1.10)] is an important metal enzyme in fungal defense against oxidative damage. Thus, we try to study whether Cu/Zn-SOD is a virulence factor in A. niger. Cu/Zn-SOD encoding gene sodC was deleted in A. niger [MA70.15 (wild type)] by homologous recombination. The deletion of sodC led to decreased SOD activity in A. niger, suggesting that sodC did contribute to full enzyme activity. ΔsodC strain showed normal mycelia growth and sporulation compared with wild type. However, sodC deletion markedly increased the cell’s sensitivity to intracellular superoxide anion generator menadione. Besides, spore germination under menadione and H2O2 stresses were significantly retarded in ΔsodC mutant compared with wild type. Further results showed that sodC deletion induced higher superoxide anion production and higher content of H2O2 and malondialdehyde (MDA) compared with wild type, supporting the role of SOD in metabolism of reactive oxygen species (ROS). Furthermore, ΔsodC mutant had a reduced virulence on chinese white pear (Pyrus bretschneideri) as lesion development by ΔsodC was significantly less than wild type. The determination of superoxide anion, H2O2, and MDA in A. niger-infected pear showed that chinese white pear infected with ΔsodC accumulated less superoxide anion, H2O2, and MDA compared with that of wild type A. niger, implying that ΔsodC induced an attenuated response in chinese white pear during fruit–pathogen interaction. Our results indicate that sodC gene contributes to the full virulence of A. niger during infection on fruit. Aspergillus niger is one of the most common species found in fungal communities. It is an important fermentation industrial strain and is also known to cause the most severe symptoms in fruit during long-term storage (Pel et al., 2007). Meanwhile, plants activate their signaling pathways to trigger defense responses to limit pathogen expansion. One of the earliest host responses after pathogen attack is oxidative burst, during which large quantities of ROS are generated by different host enzyme systems, such as glucose oxidase (Govrin and Levine, 2000). ROS such as singlet oxygen, superoxide anion, hydroxyl (OH−), and H2O2 are released to hinder the advance of pathogens (Gara et al., 2003). ROS can react with and damage cellular molecules, such as DNA, protein, and lipids, which will limit fungal propagation in the host plant (Apel and Hirt, 2004).

Characterisation of the whole-genome wide hexokinase gene family unravels the functional divergence in pear (Pyrus bretschneideri Rehd.)

ABSTRACTHexokinase genes (HXK) encode enzymes that play an important role in fruit quality and plant development because they participate in the first step of the glycolytic pathway for sugar accumulation and metabolism. In this study, the authors conducted analysis of the phylogeny, gene structure, and expression of HXK genes in pear (Pyrus bretschneideri Rehd.), comparing them with 7 other plant species. A total of 10 HXK protein sequences from pear and 33 HXKs from 7 other species were identified and clustered into 4 groups, matching their motif classification. Duplication events and motif structure variation attributed the diversification of HXK genes, supported by differential expression pattern of PbrHXKs from pear fruit transcriptome data and qRT – PCR verification. Combining pear fruit soluble sugar content data and analyses above, PbrHXK1and PbrHXK3 were identified as important candidate genes in sorbitol, fructose, and glucose accumulation during pear fruit development. PbrHXK1and PbrHXK3 were identified as important candidate genes in sorbitol, fructose, and glucose accumulation during pear fruit development. Subsequent research on these highly expressed PbrHXKs will benefit the enhancement of sugar content and quality in pear.

Response of miR156-SPL Module during the Red Peel Coloration of Bagging-Treated Chinese Sand Pear (Pyrus pyrifolia Nakai).

MicroRNA156 is an evolutionarily highly conserved plant micro-RNA (miRNA) that controls an age-dependent flowering pathway. miR156 and its target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes regulate anthocyanin accumulation in plants, but it is unknown whether this process is affected by light. Red Chinese sand pear (Pyrus pyrifolia) fruits exhibit a unique coloration pattern in response to bagging treatments, which makes them appropriate for studying the molecular mechanism underlying light-induced anthocyanin accumulation in fruit. Based on high-throughput miRNA and degradome sequencing data, we determined that miR156 was expressed in pear fruit peels, and targeted four SPL genes. Light-responsive elements were detected in the promoter regions of the miR156a and miR156ba precursors. We identified 19 SPL genes using the “Suli” pear (Pyrus pyrifolia Chinese White Pear Group) genome database, of which seven members were putative miR156 targets. The upregulated expression of anthocyanin biosynthetic and regulatory genes and downregulated expression of PpSPL2, PpSPL5, PpSPL7, PpSPL9, PpSPL10, PpSPL13, PpSPL16, PpSPL17, and PpSPL18 were observed in pear fruits after bags were removed from plants during the anthocyanin accumulation period. Additionally, miR156a/ba/g/s/sa abundance increased after bags were removed. Yeast two-hybrid results suggested that PpMYB10, PpbHLH, and PpWD40 could form a protein complex, probably involved in anthocyanin biosynthesis. Additionally, PpSPL10 and PpSPL13 interacted with PpMYB10. The results obtained in this study are helpful in understanding the possible role of miR156 and its target PpSPL genes in regulating light-induced red peel coloration and anthocyanin accumulation in pear.

Hypobaric storage reduced core browning of Yali pear fruits

Core browning is a major issue of pear fruits. The primary factor leading to development of core browning is high levels of CO2 in storage. Hypobaric storage is a new postharvest technique to extend the shelf life of fruits and can reduce CO2 partial pressure. In this study, the effect of hypobaric storage on core browning of Yali pear fruits (Pyrus bretschneideri Rehd.) was evaluated. Results showed that fruits after 0.025MPa hypobaric treatment had 37.3% lower rate of core browning development and higher acidity and soluble solid content than control fruits. In addition, 0.025MPa hypobaric treatment increased activities of cytochrome oxidase (CCO) and peroxidase (POD), and 2,2-diphenylpicrylhydrazyl (DPPH) radicals and superoxide anion scavenging capabilities. In comparison with the control, hypobaric treated fruits had lower activity of polyphenol oxidase (PPO) and higher level of total polyphenols. Hypobaric treatment also reduced an increase of succinate dehydrogenase (SDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) activities. Results indicated that hypobaric treatment could control core browning of pear fruits by regulating reactive oxygen species (ROS) generation and elimination enzymes to maintain cell membrane integrity and reduce enzymatic browning.

First Report of Pear Bitter Rot Caused by Colletotrichum fioriniae in France

HomePlant DiseaseVol. 101, No. 7First Report of Pear Bitter Rot Caused by Colletotrichum fioriniae in France PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Pear Bitter Rot Caused by Colletotrichum fioriniae in FranceD. Da Lio, R. Baroncelli, A. Weill, G. Le Floch, and P. NodetD. Da LioSearch for more papers by this author, R. Baroncellihttp://orcid.org/0000-0002-5878-1159Search for more papers by this author, A. WeillSearch for more papers by this author, G. Le FlochSearch for more papers by this author, and P. Nodethttp://orcid.org/0000-0003-3712-9783Search for more papers by this authorAffiliationsAuthors and Affiliations D. Da Lio R. Baroncelli A. Weill G. Le Floch P. Nodet , Université de Brest, EA 3882, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, IBSAM, ESIAB, Technopôle Brest-Iroise, 29280 Plouzané, France. Published Online:26 Apr 2017https://doi.org/10.1094/PDIS-01-17-0129-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Bitter rot is a common disease mainly affecting apples (Malus domestica) worldwide, and resulting in considerable economic losses, but pears can also be affected (Ivic et al. 2013). Most of the reports refer to bitter rot of Chinese and Asian pears (Pyrus bretschneideri and P. pyrifolia) caused by C. acutatum sensu lato or C. fructicola (Jiang et al. 2014; Kim et al. 2007; Li et al. 2013). To our knowledge, the only report of bitter rot on European pears (P. communis) was done by Ivic et al. (2013) in Croatia and the causal agent was identified as C. fioriniae. In the last 4 to 5 years, anthracnose symptoms have been repeatedly observed on the pear cultivar Beurré Hardy in September during harvest in an orchard near Brest, France. Lesions were round, 1 to 4 cm in diameter, brown, and dry, with acervuli, producing orange spore masses in concentric rings. Two fungal isolates were obtained (in 2015 and 2016, respectively) from symptomatic pears by culturing necrotic tissue pieces on potato dextrose agar (PDA) at 25°C in the dark. Cultures were light gray, with cottony aerial mycelium becoming darker with age and reverse ranging from brownish pink to dark gray with black spots. Cultures have dark melanized structures similar to acervuli that oozed orange-colored conidia. Conidia were cylindrical to fusiform, pointed at one or both ends, and measured 10.0 to 14.0 μm × 3.0 to 3.5 μm. Both cultural and morphological characteristics were similar to those described for C. acutatum sensu lato (Damm et al. 2012). Total genomic DNA was extracted and the rDNA ITS region was amplified using universal primers ITS4 and ITS5 then sequenced. For both isolates (UBOCC-A-116033 and UBOCC-A-116034), resulting sequences were 100% identical to C. acutatum species complex sequences. Based on Damm et al. (2012), strains were further characterized by sequencing partial ACT, CHS-1, GAPDH, HIS3, and TUB2 genes (GenBank accession nos. KY344741–52). Multilocus phylogenetic analyses carried out with the obtained and reference sequences (Damm et al. 2012) revealed that both isolates clustered within C. fioriniae, as observed using BLAST; this result was consistent with their initial identification as belonging to the C. acutatum species complex. Koch’s postulates were performed on 10 ‘Comice’ pears for each isolate. Surface sterilized fruits were wound-inoculated with 20 μl of a conidial suspension (105 conidia ml–1). After 10 days incubation at 20°C, symptoms identical to those initially observed developed around the inoculation point, while controls inoculated with water remained symptomless. Fungal colonies reisolated from the lesions were morphologically similar to the original isolates. To our knowledge, this is the first report of pear bitter rot caused by C. fioriniae in France. Moreover, to date, bitter rot was not considered as a major problem for pear growing, but as pears are the eighth largest fruit crop in production yield worldwide, pear bitter rot caused by Colletotrichum species may become a major problem in the future and require further investigation.

Penicillium and patulin distribution in pears contaminated with Penicillium expansum. Determination of patulin in pears by UHPLC-MS/MS

The danger of mycotoxin contamination entering the food supply through post-harvest infection is of perennial concern to food safety experts. To explore the distribution of Penicillium expansum and diffusion of its mycotoxin, patulin, in blue mold-damaged pears, Pyrus bretschneideri Rehd. cv. Yali obtained from markets and orchards in China were artificially inoculated with P. expansum and assayed for patulin accumulation and degree of fungal colonization. The inoculated pears were incubated until the lesions were 5, 10, 20, or 30 mm in diameter. We sampled tissue at a range of distances from the lesion, measured the spread of Penicillium by plate colony-counting methods, and used UHPLC-MS/MS to detect and quantify the patulin concentration. More P. expansum colony-forming units were isolated from pears with a higher degree of decay. Farther from the lesion, the fewer P. expansum colonies were observed, and the lower the patulin content detected. We found a significant difference in the patulin content between samples due to lesion size, and also in tissue sampled 10 mm away from the lesion. In consideration of this finding, to ensure food safety, we recommend that when a blue mold rot lesion on pear is 5, 10, or 20 mm in diameter, 20, 30, and 40 mm beyond the lesion should be removed, respectively. If a lesion surpasses 30 mm in diameter, the whole pear should be thrown away.

Phylogenetic and expression analysis of the magnesium transporter family in pear, and functional verification of PbrMGT7 in pear pollen

ABSTRACTThe magnesium ion (Mg2+) is the most abundant divalent cation in living cells, and it plays essential roles in various cellular functions. Mg2+ homeostasis in plant cells is crucial for plant growth. The MRS2/MGT family of proteins localise to various membranes, and they function during Mg2+ transport in plants, but their functions are largely unknown in fruit trees. In this study, we performed a genome-wide analysis to identify the MGT gene family members in the pear Pyrus bretschneideri. Sixteen MGT genes were identified. Analysis of the activity of pear pollen showed that a low-concentration magnesium ion treatment was beneficial for pollen germination and pollen tube growth. None of the 16 MGT genes were expressed in any unique tissue, including pollen, and their expression in magnesium-treated pollen varied greatly, where PbrMGT7 was the most sensitive and it was tested as a representative. PbrMGT7 could functionally complement a bacterial strain deficient in Mg2+, thereby indicating a role in magnesium transport. A co-localisation experiment confirmed that PbrMGT7 was localised in the mitochondria, which suggests that PbrMGT7 could mediate Mg-trafficking between the mitochondria and cytosol. Overall, these results suggest that PbrMGT7 is related to Mg2+ homeostasis during pear pollen tube growth.​​

Laboratory evaluation of differential attraction of Culex pipiens pallens to the volatiles of flowers, fruits, and seed pods

The attraction of Culex pipiens pallens Coquillett to various potential sugar sources in their habitats remains unknown. In the present study, we evaluated the attraction of Cx. pipiens pallens to the volatiles of different kinds of flowers, fruits, and seed pods by multiple choice tests under laboratory conditions. Nine of the 21 tested fresh tissues of flowers were attractive to females and six of them were attractive to males. The volatiles of six flowers (Ligustrum quihoui, Abelia chinensis, Ophiopogon japonicus, Phaseolus vulgaris, Osmanthus fragrans, and Nerium indicum) were attractive to both female and male Cx. pipiens pallens, and the flowers of Torenia fournieri and Lavandula angustifolia were potentially repellent to female and male mosquitoes, respectively. Besides, the volatiles of three fruits and seed pods (Broussonetia papyrifera, Amygdalus persica, and Cucumis melo) were attractive to both female and male Cx. pipiens pallens while the seed pods of Ficus carica and Pyrus bretschneideri were only attractive to females and males, respectively. This study provides valuable information on developing novel control methods against Cx. pipiens pallens in China.

Genome-wide identification, phylogenetic analysis, and expression profiling of the BBX family genes in pear

ABSTRACTB-box containing proteins (BBXs) are a class of zinc finger transcription factor proteins that contain one or two B-box domains and play important roles in plant growth and development. The BBX gene family has been identified in the Arabidopsis and rice genomes. However, no comprehensive identification has been reported in pear. In this study, 37 genes were identified as candidate BBXs in Chinese white pear (Pyrus bretschneideri Rehd) and denominated following the uniform nomenclature in Arabidopsis. We also performed analyses of their phylogenic relationships, structures, chromosomal locations, promoter regions, Gene Ontology (GO) annotations, and expression patterns. The identified genes were classified into five groups based on phylogeny and domain constitution analysis. PbBBXs were unevenly distributed in 12 out of 17 pear chromosomes. The cis-elements in the promoters of PbBBXs were mainly related to light, stress, and hormone response. Gene expression analysis by quantitative real-time PCR showed that PbBBXs had differential expression in different plant organs and could be classified into four major groups. PbBBXs also showed differential responses to low temperature and dehydration treatments. Overall, this study provided useful information for further functional analysis of BBXs in pear.

Genome-Wide Analysis Suggests the Relaxed Purifying Selection Affect the Evolution of WOX Genes in Pyrus bretschneideri, Prunus persica, Prunus mume, and Fragaria vesca.

WUSCHEL-related homeobox (WOX) family is one of the largest group of transcription factors (TFs) specifically found in plant kingdom. WOX TFs play an important role in plant development processes and evolutionary novelties. Although the roles of WOXs in Arabidopsis and rice have been well-studied, however, little are known about the relationships among the main clades in the molecular evolution of these genes in Rosaceae. Here, we carried out a genome-wide analysis and identified 14, 10, 10, and 9 of WOX genes from four Rosaceae species (Fragaria vesca, Prunus persica, Prunus mume, and Pyrus bretschneideri, respectively). According to evolutionary analysis, as well as amino acid sequences of their homodomains, these genes were divided into three clades with nine subgroups. Furthermore, due to the conserved structural patterns among these WOX genes, it was proposed that there should exist some highly conserved regions of microsynteny in the four Rosaceae species. Moreover, most of WOX gene pairs were presented with the conserved orientation among syntenic genome regions. In addition, according to substitution models analysis using PMAL software, no significant positive selection was detected, but type I functional divergence was identified among certain amino acids in WOX protein. These results revealed that the relaxed purifying selection might be the main driving force during the evolution of WOX genes in the tested Rosaceae species. Our result will be useful for further precise research on evolution of the WOX genes in family Rosaceae.

Genome-wide analysis suggests high level of microsynteny and purifying selection affect the evolution of EIN3/EIL family in Rosaceae.

The ethylene-insensitive3/ethylene-insensitive3-like (EIN3/EIL) proteins are a type of nuclear-localized protein with DNA-binding activity in plants. Although the EIN3/EIL gene family has been studied in several plant species, little is known about comprehensive study of the EIN3/EIL gene family in Rosaceae. In this study, ten, five, four, and five EIN3/EIL genes were identified in the genomes of pear (Pyrus bretschneideri), mei (Prunus mume), peach (Prunus persica) and strawberry (Fragaria vesca), respectively. Twenty-eight chromosomal segments of EIL/EIN3 gene family were found in four Rosaceae species, and these segments could form seven orthologous or paralogous groups based on interspecies or intraspecies gene colinearity (microsynteny) analysis. Moreover, the highly conserved regions of microsynteny were found in four Rosaceae species. Subsequently it was found that both whole genome duplication and tandem duplication events significantly contributed to the EIL/EIN3 gene family expansion. Gene expression analysis of the EIL/EIN3 genes in the pear revealed subfunctionalization for several PbEIL genes derived from whole genome duplication. It is noteworthy that according to environmental selection pressure analysis, the strong purifying selection should dominate the maintenance of the EIL/EIN3 gene family in four Rosaceae species. These results provided useful information on Rosaceae EIL/EIN3 genes, as well as insights into the evolution of this gene family in four Rosaceae species. Furthermore, high level of microsynteny in the four Rosaceae plants suggested that a large-scale genome duplication event in the EIL/EIN3 gene family was predated to speciation.

Characterization of the MAPK Gene Family and PbrMAPK13 Response to Hormone and Temperature Stresses via Different Expression Pattern in Pyrus ×bretschneideri Pollen

Mitogen-activated protein kinase (MAPK) cascades are universal signal-transduction modules, but the available information is limited in pear (Pyrus). In this study, 87 MAPK genes were identified from five Rosaceae species: chinese white pear (Pyrus ×bretschneideri cv. Dangshansuli), peach (Prunus persica), apple (Malus domestica), strawberry (Fragaria vesca), and plum (Prunus mume), 23 of which came from chinese white pear, designated as PbrMAPK. Based on the phylogenetic analysis and the architectures of conserved protein motifs of these gene sequences, MAPK family genes of five Rosaceae species were classified into two primary types (I and II) or four groups (Classes A–D). We have indicated that both segment and tandem duplications significantly contributed to the expansion of the MAPK family in Rosaceae by analysis of genomic evolution. In chinese white pear pollen, the expression analysis revealed that all PbrMAPKs could respond to temperature stresses (high/low temperature) and phytohormones, except PbrMAPK8 and PbrMAPK19 that displayed lower expressions, which suggested that PbrMAPKs play pivotal roles in signal-transduction pathways. In addition, we determined that PbrMAPK13 is located in the nucleus and plasma membranes. The lengths of pollen tubes became shorter when PbrMAPK13 was silenced by antisense oligonucleotide transfection. Our results provided an evolutionary foundation and functional characterization for MAPK gene families in chinese white pear and other plant species so as to elucidate their biological roles.

Differential gene expression analysis of \u2018Chili\u2019 (Pyrus bretschneideri) fruit pericarp with two types of bagging treatments

Preharvest bagging is a simple, grower-friendly and safe physical protection technique commonly applied to many fruits, and the application of different fruit bags can have various effects. To explore the molecular mechanisms underlying the fruit quality effects of different bagging treatments, digital gene expression (DGE) profiling of bagged and unbagged ‘Chili’ (Pyrus bretschneideri Rehd.) pear pericarp during development was performed. Relative to unbagged fruit, a total of 3022 and 769 differentially expressed genes (DEGs) were detected in the polyethylene (PE)-bagged and non-woven fabric-bagged fruit, respectively. DEGs annotated as photosynthesis-antenna proteins and photosynthesis metabolism pathway were upregulated in non-woven fabric-bagged fruit but downregulated in the PE-bagged fruit. Non-woven fabric bagging inhibited lignin synthesis in ‘Chili’ pear pericarp by downregulating DEGs involved in phenylpropanoid biosynthesis; consequently, the fruit lenticels in non-woven fabric-bagged fruit were smaller than those in the other treatments. The results indicate that the non-woven fabric bagging method has a positive effect on the appearance of ‘Chili’ pear fruit but neither of the two bagging treatments is conducive to the accumulation of soluble sugar.

A New Insight into the Evolution and Functional Divergence of SWEET Transporters in Chinese White Pear (Pyrus bretschneideri).

SWEET genes are a recently identified plant gene family that play an indispensable role in sugar efflux. However, no systematic study has been performed in pear. In this research, 18 SWEET transporters identified in pear, almost twice the number found in woodland strawberry and Japanese apricot, were divided into four clades. Conserved motifs and six exons of the SWEET transporters were found in six species. SWEET transporters contained seven transmembrane segments (TMSs) that evolved from an internal duplication of an ancestral three-TMSs unit, connected by TMS4. This is the first direct evidence identifying internal repeats through bioinformatics analysis. Whole-genome duplication (WGD) or segmental duplication and dispersed duplication represent the main driving forces for SWEET family evolution in six species, with former duplications more important in pear. Gene expression results suggested that PbSWEET15 and PbSWEET17 have no expression in any tissues because of critical lost residues and that 62.5% of PbSWEET duplicate gene pairs have functional divergence. Additionally, PbSWEET6, PbSWEET7 and PbSWEET14 were found to play important roles in sucrose efflux from leaves, and the high expression of PbSWEET1 and PbSWEET2 might contribute to unloading sucrose from the phloem in the stem. Finally, PbSWEET5, PbSWEET9 and PbSWEET10 might contribute to pollen development. Overall, our study provides important insights into the evolution of the SWEET gene family in pear and four other Rosaceae, and the important candidate PbSWEET genes involved in the development of different tissues were identified in pear.

Identification, classification, and transcription profiles of the B-type response regulator family in pear.

Type-B response regulators (B-RRs) are transcription factors that function in the final step of two-component signaling systems. In model plants, B-RRs have been shown to play important roles in cytokinin signal transduction. However, the functions of B-RRs in pear have not been well studied. In this report, we conducted a genome-wide analysis and identified 11 putative genes encoding B-PpRR proteins based on the published genome sequence of Pyrus bretschneideri. A phylogenetic tree of the B-PpRR family was constructed, and the motif distribution, chromosome localization, and gene structure of B-PpRR family genes were determined. Gene transcript profiles, which were determined from transcriptome data, indicated that B-PpRR genes potentially function during pear fruit development, bud dormancy, and light/hormone-induced anthocyanin accumulation. Treatment of the fruitlets of ‘Cuiguan’ pear (Pyrus pyrifolia), which never accumulates anthocyanin, with the cytokinin N-(2-chloro-4-pyridyl)- N′-phenylurea (CPPU) clearly induced anthocyanin accumulation. Anthocyanins accumulated in the skin of fruitlets by 16 days after CPPU treatment, along with the significant activation of most anthocyanin biosynthetic genes. Analyses of B-PpRR transcript levels suggested that B-PpRR genes mediated this accumulation of anthocyanins. These findings enrich our understanding of the function of B-PpRR genes in the physiological processes of pear.

Integrated high-density consensus genetic map of Pyrus and anchoring of the 'Bartlett' v1.0 (Pyrus communis) genome.

Genetic maps are essential tools for pear genetics and genomics research. In this study, we first constructed an integrated simple sequence repeat (SSR) and single nucleotide polymorphism (SNP)-based consensus genetic map for pear based on common SSR markers between nine published maps. A total of 5,085 markers, including 1,232 SSRs and 3,853 SNPs, were localized on a consensus map spanning 3,266.0 cM in total, with an average marker interval of 0.64 cM, which represents the highest density consensus map of pear to date. Using three sets of high-density SNP-based genetic maps with European pear genetic backgrounds, we anchored a total of 291.5 Mb of the ‘Bartlett’ v1.0 (Pyrus communis L.) genome scaffolds into 17 pseudo-chromosomes. This accounted for 50.5% of the genome assembly, which was a great improvement on the 29.7% achieved originally. Intra-genome and inter-genome synteny analyses of the new ‘Bartlett’ v1.1 genome assembly with the Asian pear ‘Dangshansuli’ (Pyrus bretschneideri Rehd.) and apple (Malus × domestica Borkh.) genomes uncovered four new segmental duplication regions. The integrated high-density SSR and SNP-based consensus genetic map provided new insights into the genetic structure patterns of pear and assisted in the genome assembly of ‘Bartlett’ through further exploration of different pear genetic maps.