## 1 Introduction  
The pear (_Pyrus_ spp.) is a major fruit crop globally and has a high economic value. According to FAO statistics, the global harvest area and production in 2021 were 1,399,484 hectares and 2,568,713 t, respectively. In the same year, the harvest area and production of pears in China were 986,479 hectares and 18,978,144 t, respectively, accounting for about 70% of the world totals ([[https://www.fao.org/faostat/zh/#data](https://www.fao.org/faostat/zh/#data)]([https://www.fao.org/faostat/zh/#data](https://www.fao.org/faostat/zh/#data)), accessed on 2 April 2023) [1]. Pears are cultivated in more than 50 countries, of which white pears (_Pyrus bretschneider_ Rehder) are the most-planted varieties in China and are often called Chinese pears [2]. In addition to being eaten as a snack fruit, pear fruit is also a traditional medicine with anti-pisamodic, anti-inflammatory, and diuretic benefits [3]. _Pyrus_ spp. 'Panguxiang', a new cultivar derived from _P. bretschneider_ Rehd. cv. 'Biyang piaoli', is sweet and crisp fruit with a special aroma and fame among consumers [4]. However, a series of problems need to be urgently studied, such as which synthetic pathways account for the accumulation and production of characteristic aromas and how related genes are expressed in the 'Panguxiang' pear.  
Volatile compounds are vital in determining the desirability of pears among consumers. Aroma is a key indicator of fruit quality [5], and a rich fruit aroma can increase consumer desire to buy, as well as improve living standards and the demand for fruits, making fruit aroma a crucial research focus [6]. The production of aroma is also a sign of ripe fruit, which is composed of different volatile compounds, many of which can be detected by the human sense of smell [7]. Aroma is an essential component of fruit quality. The aroma of many fruits has been studied in recent years, including the white pear [8], apple [9], watermelon [10], mango [11], melon [12], strawberry [13], peach [14], and tomato [15]. _P. pyrifolia_, in particular, contains more than 300 volatile compounds [16].  
The essence of fruit aroma is volatile aromatic substances, which can be divided into four categories: benzene/phenylpropane compounds, terpene compounds, fatty acid derivatives, and amino acid derivatives [17; 18]. The distribution of volatile organic compounds (VOCs) varies with fruit growth and development. In plants, terpenoids account for the largest group of VOCs [19]. Terpenoids are mainly formed from isoprenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via a complex process. According to the molar ratio of IPP to DMAPP, terpenoids can be divided into monoterpenes (1:1); sesquiterpenes and sterols (2:1); and diterpenes, carotenoids, and polyterpenes (3:1) [20]. Among them, C10 monoterpenes and C15 sesquiterpenes are the key compounds that determine the characteristic aroma of fruits [17]. In addition, sesquiterpenes are generated in the cytoplasm via the mexulonic acid (MVA) pathway, and monoterpenes are produced in cytosols and plastids via the 2-c-methylerythnitol 4-phosphate (MEP) pathway in higher plants [21; 22].  
Therefore, this study analyzes the dynamic changes in aroma composition and nutrients during the development of the 'Panguxiang' pear by combining metabolomics and transcriptomics. The variations in metabolite composition amid the growth of pear fruits and the associations between related gene expression and metabolites in the main pathways of aroma synthesis were expounded. The molecular mechanism for the synthesis of the pear was further elucidated at the transcription and metabolic levels, which underlies the comprehensive analysis of molecular and regulatory mechanisms of aroma accumulation and aroma component formation of the 'Panguxiang' fruit.