Exogenous melatonin improves pear resistance to Botryosphaeria dothidea by increasing autophagic activity and sugar/organic acid levels

Pear is a perennial deciduous fruit tree of the Rosaceae Pyrus genus, and is one of the main fruit trees worldwide. The pathogen Botryosphaeria dothidea infects pear trees and causes pear ring rot disease. According to our research, exogenous melatonin application enhanced resistance to B. dothidea in pear fruit. Melatonin treatment of pears significantly reduced the diameter of disease spots and enhanced the endogenous melatonin content under B. dothidea inoculation. Compared with H2O treatment, melatonin treatment suppressed the increase in ROS and activated ROS-scavenging enzymes. Treatment with exogenous melatonin maintained AsA-GSH at more reductive status. The expression levels of core autophagic genes and autophagosome formation were elevated by melatonin treatment in pear fruit. The silencing of PbrATG5 in Pyrus pyrifolia conferred sensitivity to inoculation, which was only slightly recovered by melatonin treatment. After inoculation with B. dothidea, exogenous melatonin treatment increased the contents of soluble sugars and organic acids in pear fruits compared with H2O treatment. Our results demonstrated that melatonin enhanced resistance to B. dothidea by increasing the autophagic activity and soluble sugar/organic acid accumulation.

Organic amendments alleviate early defoliation and increase fruit yield by altering assembly patterns and of microbial communities and enzymatic activities in sandy pear (Pyrus pyrifolia)

Severe early defoliation has become an important factor restricting the development of the pear industry in southern China. However, the assembly patterns of microbial communities and their functional activities in response to the application of bioorganic fertilizer (BIO) or humic acid (HA) in southern China’s pear orchards remain poorly understood, particularly the impact on the early defoliation of the trees. We conducted a 3-year field experiment (2017–2019) in an 18-year-old ‘Cuiguan’ pear orchard. Four fertilization schemes were tested: local custom fertilization as control (CK), CK plus HA (CK-HA), BIO, and BIO plus HA (BIO-HA). Results showed that BIO and BIO-HA application decreased the early defoliation rate by 50–60%, and increased pear yield by 40% compared with the CK and CK-HA treatments. The BIO and BIO-HA application significantly improved soil pH, available nutrient content, total enzyme activity and ecosystem multifunctionality, and also changed the structure of soil bacterial and fungal communities. The genus Acidothermus was positively correlated with the early defoliation rate, while the genus Rhodanobacter was negatively correlated. Additionally, random forest models revealed that the early defoliation rate could be best explained by soil pH, ammonium content, available phosphorus, and total enzyme activity. In conclusion, application of BIO or BIO mixed with HA could have assembled distinct microbial communities and increased total enzyme activity, leading to significant improvement of soil physicochemical traits. The increased availability of soil nutrient thus changed leaf nutrient concentrations and alleviated the early defoliation rate of pear trees in acid red soil in southern China.

A Novel Pear Scab (Venturia nashicola) Resistance Gene, Rvn3, from Interspecific Hybrid Pear (Pyrus pyrifolia × P. communis)

Asian pear scab is a fungal disease caused by Venturia nashicola. The identification of genes conferring scab resistance could facilitate the breeding of disease-resistant cultivars. Therefore, the present study aimed to identify a scab-resistance gene using an interspecific hybrid population ((Pyrus pyrifolia × P. communis) × P. pyrifolia). Artificial inoculation of V. nashicola was carried out for two years. The segregation ratio (1:1) of resistant to susceptible individuals indicated that resistance to V. nashicola was inherited from P. communis and controlled by a single dominant gene. Based on two years phenotypic data with the Kruskal–Wallis test and interval mapping, 12 common markers were significantly associated with scab resistance. A novel scab resistance gene, Rvn3, was mapped in linkage group 6 of the interspecific hybrid pear, and co-linearity between Rvn3 and one of the apple scab resistance genes, Rvi14, was confirmed. Notably, an insertion in pseudo-chromosome 6 of the interspecific hybrid cultivar showed homology with apple scab resistance genes. Hence, the newly discovered Rvn3 was considered an ortholog of the apple scab resistance gene. Since the mapping population used in the present study is a pseudo-BC1 population, pyramiding of multiple resistance genes to pseudo-BC1 could facilitate the breeding of pear cultivars with durable resistance.

A systems genetics approach reveals PbrNSC as a regulator of lignin and cellulose biosynthesis in stone cells of pear fruit

Background Stone cells in fruits of pear (Pyrus pyrifolia) negatively influence fruit quality because their lignified cell walls impart a coarse and granular texture to the fruit flesh. Results We generate RNA-seq data from the developing fruits of 206 pear cultivars with a wide range of stone cell contents and use a systems genetics approach to integrate co-expression networks and expression quantitative trait loci (eQTLs) to characterize the regulatory mechanisms controlling lignocellulose formation in the stone cells of pear fruits. Our data with a total of 35,897 expressed genes and 974,404 SNPs support the identification of seven stone cell formation modules and the detection of 139,515 eQTLs for 3229 genes in these modules. Focusing on regulatory factors and using a co-expression network comprising 39 structural genes, we identify PbrNSC as a candidate regulator of stone cell formation. We then verify the function of PbrNSC in regulating lignocellulose formation using both pear fruit and Arabidopsis plants and further show that PbrNSC can transcriptionally activate multiple target genes involved in secondary cell wall formation. Conclusions This study generates a large resource for studying stone cell formation and provides insights into gene regulatory networks controlling the formation of stone cell and lignocellulose.

PpMYB36 Encodes a MYB-Type Transcription Factor That Is Involved in Russet Skin Coloration in Pear (Pyrus pyrifolia)

Fruit color is one of the most important external qualities of pear (Pyrus pyrifolia) fruits. However, the mechanisms that control russet skin coloration in pear have not been well characterized. Here, we explored the molecular mechanisms that determine the russet skin trait in pear using the F1 population derived from a cross between russet skin (‘Niitaka’) and non-russet skin (‘Dangshansu’) cultivars. Pigment measurements indicated that the lignin content in the skin of the russet pear fruits was greater than that in the non-russet pear skin. Genetic analysis revealed that the phenotype of the russet skin pear is associated with an allele of the PpRus gene. Using bulked segregant analysis combined with the genome sequencing (BSA-seq), we identified two simple sequence repeat (SSR) marker loci linked with the russet-colored skin trait in pear. Linkage analysis showed that the PpRus locus maps to the scaffold NW_008988489.1: 53297-211921 on chromosome 8 in the pear genome. In the mapped region, the expression level of LOC103929640 was significantly increased in the russet skin pear and showed a correlation with the increase of lignin content during the ripening period. Genotyping results demonstrated that LOC103929640 encoding the transcription factor MYB36 is the causal gene for the russet skin trait in pear. Particularly, a W-box insertion at the PpMYB36 promoter of russet skin pears is essential for PpMYB36-mediated regulation of lignin accumulation and russet coloration in pear. Overall, these results show that PpMYB36 is involved in the regulation of russet skin trait in pear.

Downregulation of lncRNA PpL-T31511 and Pp-miRn182 Promotes Hydrogen Cyanamide-Induced Endodormancy Release through the PP2C-H2O2 Pathway in Pear (Pyrus pyrifolia)

Bud endodormancy is an important, complex process subject to both genetic and epigenetic control, the mechanism of which is still unclear. The endogenous hormone abscisic acid (ABA) and its signaling pathway play important roles in the endodormancy process, in which the type 2C protein phosphatases (PP2Cs) is key to the ABA signal pathway. Due to its excellent effect on endodormancy release, hydrogen cyanamide (HC) treatment is considered an effective measure to study the mechanism of endodormancy release. In this study, RNA-Seq analysis was conducted on endodormant floral buds of pear (Pyrus pyrifolia) with HC treatment, and the HC-induced PP2C gene PpPP2C1 was identified. Next, software prediction, expression tests and transient assays revealed that lncRNA PpL-T31511-derived Pp-miRn182 targets PpPP2C1. The expression analysis showed that HC treatment upregulated the expression of PpPP2C1 and downregulated the expression of PpL-T31511 and Pp-miRn182. Moreover, HC treatment inhibited the accumulation of ABA signaling pathway-related genes and hydrogen peroxide (H2O2). Furthermore, overexpression of Pp-miRn182 reduced the inhibitory effect of PpPP2C1 on the H2O2 content. In summary, our study suggests that downregulation of PpL-T31511-derived Pp-miRn182 promotes HC-induced endodormancy release in pear plants through the PP2C-H2O2 pathway.

In vitro Antiradical activity and Hepatoprotective potential of Herbal extract from Medicinal plants of Rosaceae family

The experimental study was designed to evaluate the in vitro antioxidant activity and hepatoprotective potential of ethanolic fruit extract of Pyrus pyrifolia (Burm.f.) Nakai. and Prunus avium Linn. in carbon tetrachloride (CCl4)-induced hepatotoxicity in rats. Pharmacognostic evaluation of fruits and their extracts was carried out according to the WHO quality control of herbal drugs. The antiradical activity of ethanol extracts of P. pyrifolia (Burm.f.) Nakai and P. avium L. was determined by using 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydrogen peroxide (H2O2) and nitric oxide free radical scavenging assay. The Wistar albino rats were randomly divided into seven equal groups (n = 5). Group I was treated as normal control. Group II received 0.2% carbon tetrachloride (CCL4) in olive oil (8 mL/kg, i.p) on 14th day; Groups III as standard control contained silymarin (100 mg/kg, p.o) as standard drug once daily for 14 days. Group IV and V were given P. pyrifolia (Burm.f.) Nakai extract (200 and 400 mg/kg, p.o. in olive oil) for fourteen days; Group VI and VII received P. avium Linn. extract (200 and 400 mg/kg p.o. in olive oil) for fourteen days. Group III to VII animals were treated with 0.2% CCl4 in olive oil (8mL/kg, i.p) on the 14th day after the administration (1 hour) of the standard drug and test samples. Histopathological analysis and measurement of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), total protein (TP), total albumin (TA) and total bilirubin (TB) were performed. Ethanol extract of P.avium L. demonstrated stronger antioxidant and higher total phenolic as well as total flavonoid content than P. pyrifolia (Burm.f.) Nakai. Both the extracts EEPP and EEPA (200 and 400 mg/kg) significantly normalized the CCl4-elevated levels of ALT, AST and ALP. P. pyrifolia (Burm.f.) Nakai and P. avium L. are the edible seasonal fruits that possessed an appreciable amount of phenolic and flavonoid components and could provide considerable protection against CCl4 hepatotoxicity in rodents that may be related to its antioxidant properties and also useful in preventing several degenerative and life threatening diseases.

Genome-Wide Identification of the 1-Aminocyclopropane-1-carboxylic Acid Synthase (ACS) Genes and Their Possible Role in Sand Pear (Pyrus pyrifolia) Fruit Ripening

Ethylene production is negatively associated with storage life in sand pear (Pyrus pyrifoliaNakai), particularly at the time of fruit harvest. 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) is the rate-limiting enzyme in ethylene biosynthesisand is considered to be important for fruit storage life. However, the candidate ACS genes and their roles in sand pear remain unclear. The present study identified 13ACS genes from the sand pear genome.Phylogenetic analysiscategorizedthese ACS genesinto four subgroups (type Ⅰ, type Ⅱ, type Ⅲ and putative AAT), and indicated a close relationship between sand pear and Chinese white pear (P. bretschneideri). According to the RNA-seq data and qRT-PCR analysis, PpyACS1, PpyACS2, PpyACS3, PpyACS8, PpyACS9, PpyACS12 and PpyACS13 were differently expressed in climacteric and non-climacteric-typepear fruits,‘Ninomiyahakuri’ and ‘Eli No.2′, respectively, during fruit ripening. In addition, the expressions of PpyACS2, PpyACS8, PpyACS12 and PpyACS13 werefound to be associated with system 1 of ethylene production, while PpyACS1, PpyACS3, and PpyACS9 werefound to be associated with system 2, indicating that these ACS genes have different roles in ethylenebiosynthesis during fruit development. Overall, our study provides fundamental knowledge onthe characteristics of the ACS gene family in sand pear, in addition to their possible roles infruit ripening.