Transcriptome Analysis and Ultrastructure Observation Reveal that Hawthorn Fruit Softening Is due to Cellulose/Hemicellulose Degradation

Comparative genomic and phylogenetic analyses of mitochondrial genomes of hawthorn (Crataegus spp.) in Northeast China

Hawthorn (Crataegus spp.) plants are major sources of health food and medicines. Twenty species and seven variations of Crataegus are present in China. A variety of unique Crataegus species was found in their natural distribution in northeast China. In the present study, we assembled and annotated the mitochondrial genomes of five Crataegus species from northeastern China. The sizes of the newly sequenced mitochondrial genomes ranged from 245,907 bp to 410,837 bp. A total of 45-55 genes, including 12-19 transfer RNA genes, three ribosomal RNA genes, and 29-33 protein-coding genes (PCGs) were encoded by these mitochondrial genomes. Seven divergent hotspot regions were identified by comparative analyses: atp6, nad3, ccmFN, matR, nad1, nad5, and rps1. The most conserved genes among the Crataegus species, according to the whole-genome correlation analysis, were nad1, matR, nad5, ccmFN, cox1, nad4, trnQ-TTG, trnK-TTT, trnE-TTC, and trnM-CAT. Horizontal gene transfer between organellar genomes was common in Crataegus plants. Based on the phylogenetic trees of mitochondrial PCGs, C. maximowiczii, C. maximowiczii var. ninganensis, and C. bretschneideri shared similar maternal relationships. This study improves Crataegus mitochondrial genome resources and offers important insights into the taxonomy and species identification of this genus.

Transcriptome analysis reveals genes related to the synthesis and metabolism of cell wall polysaccharides in goji berry (Lycium barbarum L.) from various regions

BACKGROUND

In goji berries (Lycium barbarum L.), the cell wall properties and ripening environment affect fruit quality and their economic benefits. However, the mechanism underlying the cell wall remains to be fully elucidated.

RESULTS

The results showed that total sugar content was higher in Qinghai berries (13.87%, P < 0.01), whereas cellulose content peaked in Zhongning berries (28%, P < 0.05). Arabinose, galactose, and galacturonic acid were the principal components of the cell wall polysaccharides in goji berries. Among them, the content of galactose in Zhongning was significantly the highest (P < 0.05). Interestingly, we found that highly expressed β-glucosidase and lowly expressed endoglucanase led to cellulose accumulation by RNA-sequencing analysis. The expression analysis results suggested that pectate lyase and pectinesterase enzymes could be major factors related to higher galactose and galacturonic acid contents in Zhongning compared to in Qinghai and Gansu. The starch and sucrose metabolism pathway, pentose and glucuronate interconversions pathway, and galactose metabolism pathway played a significant role in cell wall polysaccharide synthesis and metabolism.

CONCLUSION

In the present study, we aimed to provide some insights into the cell wall on polysaccharide composition, structural features, and gene analysis in goji berries from Zhongning, Qinghai, and Gansu in China. These results might help to clarify the molecular function of the major genes in the cell wall polysaccharides of goji berries and provide a solid foundation for further study. © 2023 Society of Chemical Industry.

Chitosan-based coating enriched with melezitose alters primary metabolites in fresh-cut pineapple during storage

Demand for minimally processed fresh fruit is increasing due to its convenience. However, the distribution of fresh-cut fruits is limited because of their short shelf life. Pineapple, a popular tropical fruit, sold in fresh-cut form has a shelf life of approximately 5-7 days at 4 °C. Chitosan, an edible coating, is commonly used to prolong the shelf life of food products. Similarly, the sugar melezitose has been reported to change during pineapple ripening and may play a role in regulating the shelf life of pineapple. However, the direct effects of this sugar have yet to be studied. The objective of this study was to investigate the effect of chitosan coating with melezitose to prolong the shelf life of fresh-cut pineapple. Full-ripe Bogor pineapples from Okinawa, Japan, were cut into cubes and soaked in either chitosan 1.25%, melezitose 5 mg/L, or chitosan+melezitose and stored for 5 days under dark conditions (23.6 ± 0.5 °C; relative humidity, 40.0 ± 10.4%). None of the treatments significantly altered the weight loss or color changes in the fresh-cut fruit. However, treatment significantly altered the primary metabolites, namely quinic acid, sucrose, and xylitol based on orthogonal projection to latent structures data with the screening from p-value score. Moreover, cell-wall metabolism is possibly affected in pineapple cut fruit treated by chitosan-melezitose as shown from metabolite sets enrichment analysis. This study showed that chitosan added with melezitose might have potential to prolong the shelf-life of fresh-cut pineapple, providing a basis for further post-harvest studies of the whole pineapple fruit.

Comparative physiological and transcriptomic analyses provide insights into fruit softening in Chinese cherry [Cerasus pseudocerasus (Lindl.) G.Don]

Fruit softening is a complex, genetically programmed and environmentally regulated process, which undergoes biochemical and physiological changes during fruit development. The molecular mechanisms that determine these changes in Chinese cherry [Cerasus peseudocerasus (Lindl.) G.Don] fruits are still unknown. In the present study, fruits of hard-fleshed 'Hongfei' and soft-fleshed 'Pengzhoubai' varieties of Chinese cherry were selected to illustrate the fruit softening at different developmental stages. We analyzed physiological characteristics and transcriptome profiles to identify key cell wall components and candidate genes related to fruit softening and construct the co-expression networks. The dynamic changes of cell wall components (cellulose, hemicellulose, pectin, and lignin), the degrading enzyme activities, and the microstructure were closely related to the fruit firmness during fruit softening. A total of 6,757 and 3,998 differentially expressed genes (DEGs) were screened between stages and varieties, respectively. Comprehensive functional enrichment analysis supported that cell wall metabolism and plant hormone signal transduction pathways were involved in fruit softening. The majority of structural genes were significantly increased with fruit ripening in both varieties, but mainly down-regulated in Hongfei fruits compared with Pengzhoubai, especially DEGs related to cellulose and hemicellulose metabolism. The expression levels of genes involving lignin biosynthesis were decreased with fruit ripening, while mainly up-regulated in Hongfei fruits at red stage. These obvious differences might delay the cell all degrading and loosening, and enhance the cell wall stiffing in Hongfei fruits, which maintained a higher level of fruit firmness than Pengzhoubai. Co-expressed network analysis showed that the key structural genes were correlated with plant hormone signal genes (such as abscisic acid, auxin, and jasmonic acid) and transcription factors (MADS, bHLH, MYB, ERF, NAC, and WRKY). The RNA-seq results were supported using RT-qPCR by 25 selected DEGs that involved in cell wall metabolism, hormone signal pathways and TF genes. These results provide important basis for the molecular mechanism of fruit softening in Chinese cherry.

Secretome Analysis for a New Strain of the Blackleg Fungus Plenodomus lingam Reveals Candidate Proteins for Effectors and Virulence Factors

The fungal secretome is the main interface for interactions between the pathogen and its host. It includes the most important virulence factors and effector proteins. We integrated different bioinformatic approaches and used the newly drafted genome data of P. lingam isolate CAN1 (blackleg of rapeseed fungus) to predict the secretion of 217 proteins, including many cell-wall-degrading enzymes. All secretory proteins were identified; 85 were classified as CAZyme families and 25 were classified as protease families. Moreover, 49 putative effectors were predicted and identified, where 39 of them possessed at least one conserved domain. Some pectin-degrading enzymes were noticeable as a clustering group according to STRING web analysis. The secretome of P. lingam CAN1 was compared to the other two blackleg fungal species (P. lingam JN3 and P. biglobosus CA1) secretomes and their CAZymes and effectors were identified. Orthologue analysis found that P. lingam CAN1 shared 14 CAZy effectors with other related species. The Pathogen-Host Interaction database (PHI base) classified the effector proteins in several categories where most proteins were assigned as reduced virulence and two of them termed as hypervirulence. Nowadays, in silico approaches can solve many ambiguous issues about the mechanism of pathogenicity between fungi and plant host with well-designed bioinformatics tools.

Integrative metabolome and transcriptome analyses reveals the black fruit coloring mechanism of Crataegus maximowiczii C. K. Schneid

Crataegus is an economically important plant due to its medicinal and health-promoting properties. Flavonoids are the main functional components of Crataegus fruit. Fruits of naturally pollinated Crataegus maximowiczii possess an extraordinary black skin and are rich in anthocyanins and other flavonoids. However, the composition of anthocyanins and the overall molecular mechanism of anthocyanin biosynthesis in C. maximowiczii fruits have not been fully elucidated. In this study, the metabolome and transcriptome of C. maximowiczii fruits with black and red skin were analyzed. The results revealed that the differential metabolites and genes were enriched in the anthocyanin biosynthesis pathways in C. maximowiczii fruits. In total, 52 differentially accumulated flavonoid metabolites, 12 differentially accumulated anthocyanins and 22 differentially expressed genes were identified. After weighted gene coexpression network analysis, two modules were found to be highly interrelated with the accumulation of anthocyanin components. The coexpression networks of these two modules were used to identify key candidate transcription factors associated with anthocyanin biosynthesis, such as MYB5, MYB113, bHLH60, ERF105, bZIP44, NAC082, and WRKY11. The results revealed that cyanidin-based anthocyanins were the main pigments responsible for the black coloration of C. maximowiczii fruits. Based on these differentially accumulated anthocyanins and key genes, genetic and metabolic regulatory networks of anthocyanin biosynthesis were also proposed. Overall, this study elucidates the molecular basis of the formation of black color in C. maximowiczii fruits, and provides an intensive study on anthocyanin biosynthesis in C. maximowiczii for comprehensive utilization.

Abscisic acid-responsive transcription factors PavDof2/6/15 mediate fruit softening in sweet cherry

Softening is a key step during fruit ripening that is modulated by the interplay between multiple phytohormones. The antagonistic action of abscisic acid (ABA) and auxin determines the rate of fruit ripening and softening. However, the transcription factors that integrate ABA and auxin signals to regulate fruit softening remain to be determined. In this study, we identified several DNA-binding with One Finger (Dof) transcription factors essential for ABA-promoted fruit softening, based on transcriptome analysis of two sweet cherry (Prunus avium L.) varieties with different fruit firmness. We show that PavDof6 directly binds to the promoters of genes encoding cell wall-modifying enzymes to activate their transcription, while PavDof2/15 directly repress their transcription. Transient overexpression of PavDof6 and PavDof2/15 in sweet cherry fruits resulted in precocious and delayed softening, respectively. In addition, we show that the auxin response factor PavARF8, the expression of whose encoding gene is repressed by ABA, activates PavDof2/15 transcription. Furthermore, PavDof2/6/15 and PavARF8 directly bind to the 9-cis-epoxycarotenoid dioxygenase 1 (PavNCED1) promoter and regulate its expression, forming a feedback mechanism for ABA-mediated fruit softening. These findings unveil the physiological framework of fruit softening and establish a direct functional link between the ABA-PavARF8-PavDofs module and cell-wall-modifying genes in mediating fruit softening.

Influence of thermal processing on the quality of hawthorn: quality markers of heat-processed hawthorn

Hawthorn and its derived products are used worldwide as foods as well as complementary medicine. During the preparation of hawthorn, heating and thermal processing are frequently reported. The thermal processing will change the medicinal purposes and modify the efficacy of hawthorn. However, details including the chemical profile shifting and quality markers of heat-processed hawthorn have not been well understood. In the paper, we analyzed the hawthorn samples processed at different temperatures and different times by ultraviolet visible absorption spectrum and LC-MS technologies combined with multivariate statistical analysis. It was revealed for the first time that thermal processing could greatly change the ultraviolet visible absorption spectra and chemical profiles of hawthorn even with heat treatment at 130°C for 10 minutes. And the ultraviolet visible absorption spectrum, especially the ratio value (R_{A500 nm/400 nm} ), was a descriptive and qualitative indicator of heating degree for the thermal processing at the macroscopic level. Several components, such as hyperoside, chlorogenic acid, quercetin and apigenin, decreased or increased in content during the processing, and they could be utilized as the chemical quality markers. The proposed quality markers for heat-processed hawthorn will be helpful for further optimizing the processing conditions of hawthorn. This article is protected by copyright. All rights reserved.

Cultivated hawthorn (Crataegus pinnatifida var. major) genome sheds light on the evolution of Maleae (apple tribe)

Cultivated hawthorn (Crataegus pinnatifida var. major) is an important medicinal and edible plant with a long history of use for health protection in China. Herein, we provide a de novo chromosome-level genome sequence of the hawthorn cultivar "Qiu Jinxing." We assembled an 823.41 Mb genome encoding 40 571 genes and further anchored the 779.24 Mb sequence into 17 pseudo-chromosomes, which account for 94.64% of the assembled genome. Phylogenomic analyses revealed that cultivated hawthorn diverged from other species within the Maleae (apple tribe) at approximately 35.4 Mya. Notably, genes involved in the flavonoid and triterpenoid biosynthetic pathways have been significantly amplified in the hawthorn genome. In addition, our results indicated that the Maleae share a unique ancient tetraploidization event; however, no recent independent whole-genome duplication event was specifically detected in hawthorn. The amplification of non-specific long terminal repeat retrotransposons contributed the most to the expansion of the hawthorn genome. Furthermore, we identified two paleo-sub-genomes in extant species of Maleae and found that these two sub-genomes showed different rearrangement mechanisms. We also reconstructed the ancestral chromosomes of Rosaceae and discussed two possible paleo-polyploid origin patterns (autopolyploidization or allopolyploidization) of Maleae. Overall, our study provides an improved context for understanding the evolution of Maleae species, and this new high-quality reference genome provides a useful resource for the horticultural improvement of hawthorn.

Characterization of Fruit Development, Antioxidant Capacity, and Potential Vasoprotective Action of Peumo (Cryptocarya alba), a Native Fruit of Chile

The peumo (Cryptocarya alba) is a native fruit from central Chile that belongs to the Lauraceae family. To characterize the development and the potential health benefits of this edible fruit, quality and physiological parameters, along with antioxidant capacity, were evaluated during three clearly defined developmental stages of the fruit in two seasons. The most distinguishable attributes of ripe fruit were the change in size and color. Low CO₂ production and no detectable ethylene levels suggested non-climacteric behavior of the peumo fruit. Peumo demonstrate a significant increase in their antioxidant capacity per 1 g of fresh weight (FW) of the sample, from small to ripe fruit. Higher values in ripe fruit (FRAP: 37.1–38.3 µmol FeSO4/gFW, TEAC: 7.9–8.1 mmol TE/gFW, DPPH: 8.4-8.7 IC₅₀ μg/mL, and ORAC: = 0.19–0.20 mmol TE/gFW) were observed than those in blueberry fruit (FRAP: 4.95 µmol FeSO4/gFW, TEAC: 1.25 mmol TE/gFW, DPPH: 11.3 IC₅₀ μg/mL, and ORAC: 0.032 mmol TE/ gFW). The methanol extracts of ripe fruit displayed the presence of polyphenol acids and quercetin, an ORAC value of 0.637 ± 0.061 mmol TE per g dried weight (DW), and a high cellular antioxidant and anti-inflammatory potential, the latter exceeding the effect of quercetin and indomethacin used as standard molecules. Also, the assay of isolated rat aorta with endothelium-dependent relaxation damage demonstrated that the peumo extract induced vascular protection, depending on its concentration under a high glucose condition. These results demonstrate that these endemic fruits have a good chance as ingredients or foods with functional properties.

The complete chloroplast genome of Crataegus bretschneideri Schneid. (Rosaceae)

Crataegus bretschneideri Schneid., with an unclear phylogenic position, is mainly distributed in northeast and inner mongolia area of China. In this study, the complete chloroplast genome sequence of C. bretschneideri was determined by using Illumina high-throughput sequencing method. The chloroplast genome was 159,607 bp in length and consisted of a large single-copy (LSC) region (87,601 bp), a small single-copy (SSC) region (19,312 bp), separated by a pair of inverted repeat (IRs: 26,347 bp, each) regions. It comprised a total of 114 unique genes, including 80 protein-coding genes, 30 tRNA genes, and 4 rRNA genes. Phylogenetic analysis based on complete chloroplast genomes indicated that C. bretschneideri was closely related to C. marshallii Eggl in the subfamily Maloideae. This complete chloroplast genome will provide valuable insight into evolution, molecular breeding, and phylogenetic analysis of Crataegus species.

In Vitro Secretome Analysis Suggests Differential Pathogenic Mechanisms between Fusarium oxysporum f. sp. cubense Race 1 and Race 4

Banana Fusarium wilt, caused by the fungus pathogen Fusarium oxysporum f. sp. cubense (Foc), is a devastating disease that causes tremendous reductions in banana yield worldwide. Secreted proteins can act as pathogenicity factors and play important roles in the Foc-banana interactions. In this study, a shotgun-based proteomic approach was employed to characterize and compare the secretomes of Foc1 and Foc4 upon banana extract treatment, which detected 1183 Foc1 and 2450 Foc4 proteins. Comprehensive in silico analyses further identified 447 Foc1 and 433 Foc4 proteins in the classical and non-classical secretion pathways, while the remaining proteins might be secreted through currently unknown mechanisms. Further analyses showed that the secretomes of Foc1 and Foc4 are similar in their overall functional characteristics and share largely conserved repertoires of CAZymes and effectors. However, we also identified a number of potentially important pathogenicity factors that are differentially present in Foc1 and Foc4, which may contribute to their different pathogenicity against banana hosts. Furthermore, our quantitative PCR analysis revealed that genes encoding secreted pathogenicity factors differ significantly between Foc1 and Foc4 in their expression regulation in response to banana extract treatment. To our knowledge, this is the first experimental secretome analysis that focused on the pathogenicity mechanism in different Foc races. The results of this study provide useful resources for further exploration of the complicated pathogenicity mechanisms in Foc.

New Insight into the Phylogeny and Taxonomy of Cultivated and Related Species of Crataegus in China, Based on Complete Chloroplast Genome Sequencing

Hawthorns (Crataegus L.) are one of the most important processing and table fruits in China, due to their medicinal properties and health benefits. However, the interspecific relationships and evolution history of cultivated Crataegus in China remain unclear. Our previously published data showed C. bretschneideri may be derived from the hybridization of C. pinnatifida with C. maximowiczii, and that introgression occurs between C. hupehensis, C. pinnatifida, and C. pinnatifida var. major. In the present study, chloroplast sequences were used to further elucidate the phylogenetic relationships of cultivated Crataegus native to China. The chloroplast genomes of three cultivated species and one related species of Crataegus were sequenced for comparative and phylogenetic analyses. The four chloroplast genomes of Crataegus exhibited typical quadripartite structures and ranged from 159,607 bp (C. bretschneideri) to 159,875 bp (C. maximowiczii) in length. The plastomes of the four species contained 113 genes consisting of 79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes. Six hypervariable regions (ndhC-trnV(UAC)-trnM(CAU), ndhA, atpH-atpI, ndhF, trnR(UCU)-atpA, and ndhF-rpl32), 196 repeats, and a total of 386 simple sequence repeats were detected as potential variability makers for species identification and population genetic studies. In the phylogenomic analyses, we also compared the entire chloroplast genomes of three published Crataegus species: C. hupehensis (MW201730.1), C. pinnatifida (MN102356.1), and C. marshallii (MK920293.1). Our phylogenetic analyses grouped the seven Crataegus taxa into two main clusters. One cluster included C. bretschneideri, C. maximowiczii, and C. marshallii, whereas the other included C. hupehensis, C. pinnatifida, and C. pinnatifida var. major. Taken together, our findings indicate that C. maximowiczii is the maternal origin of C. bretschneideri. This work provides further evidence of introgression between C. hupehensis, C. pinnatifida, and C. pinnatifida var. major, and suggests that C. pinnatifida var. major might have been artificially selected and domesticated from hybrid populations, rather than evolved from C. pinnatifida.

Comparative Analysis of Akebia trifoliata Fruit Softening at Different Flesh Ripening Stages Using Tandem Mass Tag Technology

Owing to its medicinal and high nutritional values, Akebia trifoliata can be considered as a new type of medicinal and edible homologous resources, and it has begun to be widely cultivated in many areas of China. Over-softening of fruit would affect the sensorial quality, utilization rate, and consumer acceptance of the fruit postharvest. However, fruit softening has not been characterized and the molecular mechanism underlying A. trifoliata fruit softening during ripening remains unclear. A comparative proteomic analysis was performed on the fruit at three developmental stages using tandem mass tag technology. In total, 2,839 proteins and 302 differentially abundant proteins (DAPs) were identified. Bioinformatics analysis indicated that most DAPs were implicated in oxidoreductase activity, protein domain-specific binding and pyruvate metabolism. Moreover, 29 DAPs associated with cell wall metabolism, plant hormone, and stress and defense response pathways were validated using quantitative PCR. Notably, pectinesterase, pectate lyase, and β-galactosidase, which are involved in cell wall degradation, as well as gibberellin regulated protein, cysteine protease, thaumatin-like protein and heat shock proteins which is involved in plant hormone, and stress and defense response, were significantly up-regulated in softening fruit compared with the levels in non-softening fruit. This indicated that they might play key roles in A. trifoliata fruit softening. Our findings will provide new insights into potential genes influencing fruit softening traits of A. trifoliata, which will help to develop strategies to improve fruit quality and reduce softening-related losses.

The complete chloroplast genome of Crataegus hupehensis Sarg. (Rosaceae), a medicinal and edible plant in China

Crataegus hupehensis Sarg. is well-known for its medicinal and nutritive value. In this study, the complete chloroplast genome sequence of C. hupehensis was determined by using Illumina high-throughput sequencing approach. The complete chloroplast genome is 159,766 bp with 36.6% GC content. It contained a pair of inverted repeat regions of 26,385 bp, a large single-copy region of 87,852 bp, and a small single-copy region of 19,144 bp. It contained 112 distinct genes, including 78 protein-coding genes, 4 ribosomal RNA genes, and 30 transfer RNA genes. Phylogenetic analysis based on chloroplast genomes indicated that C. hupehensisis was closely related to C. kansuensis and C. marshallii in the subfamily Maloideae. This complete chloroplast genome will provide valuable insight into evolution, molecular breeding, and phylogenetic analysis of Crataegus species.

Transcriptome analysis of table grapes (Vitis vinifera L.) identified a gene network module associated with berry firmness

Berry firmness is one of the main selection criteria for table grape breeding. However, the underlying genetic determinants and mechanisms involved in gene expression during berry development are still poorly understood. In this study, eighteen libraries sampled from Vitis vinifera L. cv. ‘Red Globe’ and ‘Muscat Hamburg’ at three developmental stages (preveraison, veraison and maturation) were analyzed by RNA sequencing (RNA-Seq). The firmness of ‘Red Globe’ was significantly higher than that of ‘Muscat Hamburg’ at the three developmental stages. In total, a set of 4,559 differentially expressed genes (DEGs) was identified between ‘Red Globe’ and ‘Muscat Hamburg’ in the preveraison (2,259), veraison (2030) and maturation stages (2682), including 302 transcription factors (TFs). Weighted gene coexpression network analysis (WGCNA) showed that 23 TFs were predicted to be highly correlated with fruit firmness and propectin content. In addition, the differential expression of the PE, PL, PG, β-GAL, GATL, WAK, XTH and EXP genes might be the reason for the differences in firmness between ‘Red Globe’ and ‘Muscat Hamburg’. The results will provide new information for analysis of grape berry firmness and softening.

Changes in water loss and cell wall metabolism during postharvest withering of tobacco (Nicotiana tabacum L.) leaves using tandem mass tag-based quantitative proteomics approach

Withering is an important biological process accompanied by dehydration and cell wall metabolism in postharvest plant organs during curing/processing and storage. However, dynamics involved in cell wall metabolism and resultant water loss during withering in postharvest tobacco leaves is not well-documented. Here, tandem mass tag (TMT)-based quantitative proteomic analysis in postharvest tobacco leaves (cultivar K326) under different withering conditions was performed. In total, 11,556 proteins were detected, among which 496 differentially abundant proteins (DAPs) were identified. To elucidate the withering mechanism of tobacco leaves, 27 DAPs associated with cell wall metabolism were screened. In particular, pectin acetylesterases, glucan endo-1,3-beta-glucosidases, xyloglucan endotransglucosylase/hydrolase, alpha-xylosidase 1-like, probable galactinol-sucrose galactosyltransferases, endochitinase A, chitotriosidase-1-like and expansin were the key proteins responsible for the withering of postharvest tobacco leaves. These DAPs were mainly involved in pectin metabolism, cellulose, hemicellulose and galactose metabolism, amino sugar and nucleotide sugar metabolism as well as cell wall expansion. Furthermore, relative water content and softness values were significantly and positively correlated. Thus, dehydration and cell wall metabolism were crucial for tobacco leaf withering under different conditions. Nine candidate DAPs were confirmed by parallel reaction monitoring (PRM) technique. These results provide new insights into the withering mechanism underlying postharvest physiological regulatory networks in plants/crops.

Transcriptome analysis reveals delaying of the ripening and cell-wall degradation of kiwifruit by hydrogen sulfide

BACKGROUND

Hydrogen sulfide (H₂ S) is a known signaling molecule in plants, which has the ability to delay fruit ripening. Our previous studies have shown that H₂ S treatment could delay the maturation of kiwifruits by inhibiting ethylene production, improving protective enzyme activities, and decreasing the accumulation of reactive oxygen species to protect the cell membrane during storage. The mechanism related to the way in which H₂ S affected kiwifruit maturation was still unclear. We performed transcriptome sequencing to explore the influences of H₂ S on the softening of kiwifruit.

RESULTS

The firmness and the soluble solids content (SSC) of the kiwifruit were significantly better maintained with H₂ S treatment compared to the control during the storage period (P < 0.05). Transmission electron microscopy (TEM) showed that degradation of the cell wall was inhibited after H₂ S treatment. Based on transcriptome data analysis and quantitative real-time polymerase chain reaction (qRT-PCR), expression levels of endo-1,4-β-glucanase (β-glu), β-galactosidase (β-gal) and pectinesterase (PME) decreased whereas pectinesterase inhibitor (PMEI) significantly increased in response to H₂ S. The members of the signal transduction pathway involved in ethylene were also identified. Hydrogen sulfide inhibited the expression of ethylene receptor 2 (ETR2), ERF003, ERF5, and ERF016, and increased the expression of ethylene-responsive transcription factor 4 (ERF4) and ERF113.

CONCLUSION

Hydrogen sulfide could delay the ripening and senescence of kiwifruit by regulating the cell-wall degrading enzyme genes and affecting ethylene signal transduction pathway genes. Our results revealed the effect of H₂ S treatment on the softening of kiwifruit at the transcription level, laying a foundation for further research. © 2020 Society of Chemical Industry.

Molecular Analysis of Evolution and Origins of Cultivated Hawthorn (Crataegus spp.) and Related Species in China

Hawthorn is of high economic value owing to its medicinal properties and health benefits. Crataegus is a member of the Rosaceae family; the genus has a complicated taxonomic history, and several theories on its origin have been proposed. In this study, 53 accessions from seven Crataegus taxa native to China and accessions of exotic Crataegus species (two from Europe and one from North America) were analyzed by specific locus amplified fragment sequencing (SLAF-seq). In total, 933,450 single-nucleotide polymorphisms were identified after filtering and used to investigate the species' genomic evolution. Phylogenetic trees derived from nuclear simple sequence repeats (SSRs) and SLAF-seq data showed the same topology, in which Crataegus maximowiczii and Crataegus sanguineae formed a closely related cluster that was clearly separated from the cluster composed of Crataegus hupehensis, Crataegus pinnatifida, Crataegus pinnatifida var. major, Crataegus bretschneideri and Crataegus scabrifolia. Phylogenetic and structure analysis indicated that the seven Chinese Crataegus taxa had two separate speciation events. Plants that evolved the southwestern route shared the genepool with the European species, whereas plants along the northeastern route shared the genepool with the North American species. TreeMix genetic analysis revealed that C. bretschneideri may have a hybrid origin. This study provides valuable information on the origins of Chinese Crataegus and suggests an evolutionary model for the main Crataegus species that native to China.

An RNA Sequencing Transcriptome Analysis and Development of EST-SSR Markers in Chinese Hawthorn through Illumina Sequencing

Chinese hawthorn (Crataegus pinnatifida) is an important ornamental and economic horticultural plant. However, the lack of molecular markers has limited the development and utilization of hawthorn germplasm resources. Simple sequence repeats (SSRs) derived from expressed sequence tags (ESTs) allow precise and effective cultivar characterization and are routinely used for genetic diversity analysis. Thus, we first reported the development of polymorphic EST-SSR markers in C. pinnatifida with perfect repeats using Illumina RNA-Seq technique. In total, we investigated 14,364 unigenes, from which 5091 EST-SSR loci were mined. Di-nucleotides (2012, 39.52%) were the most abundant SSRs, followed by mono- (1989, 39.07%), and tri-nucleotides (1024, 20.11%). On the basis of these EST-SSRs, a total of 300 primer pairs were designed and used for polymorphism analysis in 70 accessions collected from different geographical regions of China. Of 239 (79.67%) pairs of primer-generated amplification products, 163 (54.33%) pairs of primers showed polymorphism. Finally, 33 primers with high polymorphism were selected for genetic diversity analysis and tested on 70 individuals with low-cost fluorescence-labeled M13 primers using capillary electrophoresis genotyping platform. A total of 108 alleles were amplified by 33 SSR markers, with the number of alleles (Na) ranging from 2 to 14 per locus (mean: 4.939), and the effective number of alleles (Ne) ranging from 1.258 to 3.214 (mean: 2.221). The mean values of gene diversity (He), observed heterozygosity (Ho), and polymorphism information content (PIC) were 0.524 (range 0.205–0.689), 0.709 (range 0.132–1.000), and 0.450 (range 0.184–0.642), respectively. Furthermore, the dendrogram constructed based on the EST-SSR separated the cultivars into two main clusters. In sum, our study was the first comprehensive study on the development and analysis of a large set of SSR markers in hawthorn. The results suggested that the use of NGS techniques for SSR development represented a powerful tool for genetic studies. Additionally, fluorescence-labeled M13 markers proved to be a valuable method for genotyping. All of these EST-SSR markers have agronomic potential and constitute a scientific basis for future studies on the identification, classification, and innovation of hawthorn germplasms.

White-rot fungi pretreatment combined with alkaline/oxidative pretreatment to improve enzymatic saccharification of industrial hemp

White-rot fungi combined with alkaline/oxidative (A/O) pretreatments of industrial hemp woody core were proposed to improve enzymatic saccharification. In this study, hemp woody core were treated with only white rot fungi, only A/O and combined with the two methods. The results showed that Pleurotus eryngii (P. eryngii) was the most effective fungus for pretreatment. Reducing sugars yield was 329mg/g with 30 Filter Paper Unit (FPU)/g cellulase loading when treated 21day. In the A/O groups, the results showed that when treated with 3% NaOH and 3% H₂O₂, the yield of reducing sugars was 288mg/g with 30FPU/g cellulase loading. After combination pretreatment with P. eryngii and A/O pretreatment, the reducing sugar yield from enzymatic hydrolysis of combined sample increased 1.10-1.29-fold than that of bio-treated or A/O pretreatment sample at the same conditions, suggesting that P. eryngii combined with A/O pretreatment was an effective method to improve enzyme hydrolysis.