Pears are popular table fruits, grown and consumed worldwide for their excellent color, aroma, and taste. Volatile aroma is an important factor affecting fruit quality, and the fatty acid metabolism pathway is important in synthesizing volatile aromas. Most of the white pear varieties cultivated in China are not strongly scented, which significantly affects their overall quality. Panguxiang is a white pear cultivar, but its aroma has unique components and is strong. The study of the mechanisms by which aroma is formed in Panguxiang is, therefore, essential to improving the quality of the fruit. The study analyzed physiological and transcriptome factors to reveal the molecular network behind volatile aroma formation in Panguxiang. The samples of Panguxiang fruit were collected in two (fruit development at 60, 90, 120, and 147 days, and fruit storage at 0, 7, 14, 21, and 28 days) periods. A total of nine sample stages were used for RNA extraction and paired-end sequencing. In addition, RNA quantification and qualification, library preparation and sequencing, data analysis and gene annotation, gene co-expression network analysis, and validation of DEGs through quantitative real-time PCR (qRT-;PCR) were performed in this study. The WGCNA identified yellow functional modules and several biological and metabolic pathways related to fatty acid formation. Finally, we identified seven and eight hub genes in the fatty acid synthesis and fatty acid metabolism pathways, respectively. Further analysis of the co-expression network allowed us to identify several key transcription factors related to the volatile aroma, including AP2/ERF-ERF, C3H, MYB, NAC, C2H2, GRAS, and Trihelix, which may also be involved in the fatty acid synthesis. This study lays a theoretical foundation for studying volatile compounds in pear fruits and provides a theoretical basis for related research in other fruits.

Volatiles are essential substances that determine distinct fruit flavors and user preferences. However, the metabolic dynamic and molecular modulation models that regulate the overall flavor generation during fruit growth and ripening are still largely unclear for most fruit species. To comprehensively analyze the molecular mechanism and regulation mechanism of aroma accumulation and aroma component formation in Pyrus spp. ‘Panguxiang’ (‘Panguxiang’pear), this study compared pear phenotype, sugars, organic acid content, and the expression of related genes and metabolites amid pear growth and development in Pyrus spp. ‘Panguxiang’. A total of 417 VOCs (4 amines, 19 aromatics, 29 aldehydes, 31 alcohols, 38 ketones, 64 heterocyclic compounds, 89 terpenoids, 94 esters, and 49 others) were found. The potential gene expression patterns were explored by combining transcriptomics and metabolomics, and VOC-associated metabolism and transcriptome data from all samples were integrated during the growth and development period. On this basis, we constructed a colorful model depicting changes in the VOCs and genes throughout pear growth and development. Our findings reveal that terpenoid biosynthesis pathways are the main aroma production pathways during pear growth and development. In addition to providing novel insights into the metabolic control of fruit flavor during growth and development, this study also provides a new theoretical basis for studying aroma metabolites in pears.

Idesia polycarpa is a dioecious tree; in field surveys, there are rare sex conversions in I. polycarpa individuals with bisexual flowers. To identify the molecular mechanisms underlying sex conversion in this species, an integrative analysis of the proteome and transcriptome profiles of I. polycarpa male and bisexual flowers at key developmental stages was conducted in this study using isobaric tags for relative and absolute quantification and RNA-seq technology. A total of 15,003 proteins were identified; the differentially expressed proteins (DEPs) were enriched in metabolic pathways, biosynthesis of secondary metabolites, and flavonoid metabolism pathways in all comparison groups. A total of 290,442 unigenes were obtained; these were compared with seven databases, revealing 196,366 annotated unigenes. In general, the expression of proteins and genes tended to be positively correlated, with Spearman correlation coefficients in the ranges of 0.152–0.262 (all genes and all proteins) and 0.497–0.778 (DEPs and DEGs). The integrative analysis of DEPs and DEGs between male and bisexual flowers revealed that the most significantly enriched pathways were flavonoid pathways, metabolic pathways, and the biosynthesis of secondary metabolites. Finally, four co-expressed proteins and transcripts and one gene associated with the flavonoid biosynthesis pathway were screened out. The proteins identified were p-coumaroyl shikimate 3′-hydroxylase, and shikimate/quinate hydroxycinnamoyl transferase, and the gene was caffeoyl-CoA O-methyltransferase. The analysis has revealed key potential proteins and genes involved in sex conversion at the molecular level and has provided a basis for future investigations of artificial regulation of sex differentiation in I. polycarpa.

Aroma is an appreciated fruit property, and volatile flavor plays a key role in determining the perception and acceptability of fruit products by consumers. However, metabolite composition that contributes to the aroma in fruit quality is unclear. In this study, we detected 645 volatile organic compounds of ‘Panguxiang’ pear in total, including esters, alcohols, alkanes, acids, ketones, terpenes and aldehydes. In addition, the levels of sugars, organic acids and amino acids in ‘Panguxiang’ pear were investigated using high-performance liquid chromatography. In the aroma generation, glucose was the dominant sugar, followed by sucrose and fructose. At the development transferred storage stage, organic acids may not participate in aroma biosynthesis. The amino acids that may play potential roles in aroma substance synthesis are tyrosine and glycine. Through metabolomics analysis at different stages of ‘Panguxiang’ pear, we selected 65 key metabolites that were significantly related to glucose, sucrose, fructose, tyrosine and glycine, according to the trends of metabolite concentrations. Finally, we chose eight candidate metabolites (e.g., three esters, two aldehydes, one alcohol, one acid and one ketone) as the representative aroma substances of the ‘Panguxiang’ pear compared to the metabolome of the ‘Korla’ at stage Z5. Data and results from this study can help better understand the variations in aroma quality among pear varieties and assist in developing breeding programs for pear varieties.