Integrated metabonomics and transcriptomics analysis of fruit sugar biosynthesis in two pear cultivars with different sugar contents

• Glucose, fructose, sucrose, and sorbitol were the predominant sugar species in sand pears. • Metabolomic and transcriptomic profiles of sugar contents have been characterized in two pear cultivars. • Transcription factors also played key roles in the differential accumulation of sugars in 'ZL' and 'LY'. Sand pears with high sugar content are highly favored by consumers. The contents and accumulation mechanisms of key sugars vary among different sand pear cultivars. In this study, we examined the profiles of sugar metabolites and the expression of genes related to sugar metabolism in two pear cultivars with differing sugar dynamics, using integrated metabolomics and transcriptomics. Our results showed that fructose, sucrose, glucose and sorbitol were the predominant soluble sugars in sand pear. The contents of sucrose and fructose were 7-fold and 1.5-fold higher in ‘Zheli No.6′ (ZL, high sugar pear cultivar) than in ‘Lvyun’ (LY, low sugar pear cultivar) at the ripening stage. In contrast, the content of glucose was lower in ZL than in LY and no difference in the content of sorbitol was observed at the ripening stage. This result showed that the contents of sucrose and fructose were the key factors influencing the sweetness of ‘ZL’ and ‘LY’ pears. There are sixteen candidate genes encoding key enzymes (sucrose phosphate synthase, alkaline/neutral invertase, fructokinase and hexokinase) involved in sucrose and fructose biosynthesis, two sugar transporters [polyol monosaccharide transporter ( PMT ) and sugars will eventually be exported transporter proteins ( SWEET )] and fifty-seven transcription factors ( TFs ), whose expression patterns correlated with those of genes involved in the sucrose and fructose biosynthesis. Correlation analysis revealed that the differences in sucrose and fructose contents between ‘ZL’ and ‘LY’ were strongly correlated with the expression levels of structural genes and transporter genes, such as SPS (EVM0021473, EVM0033049, EVM0002612, etc.), A/N-Inv (ONT.19849 and EVM0035833), FRK (EVM0027038), SWEET (EVM0022199), and PMT (EVM0014639), as well as related transcription factor (TF) genes ( bHLH, bZIP, EIL, ERF, MYB, NAC , and WRKY ) involved in sugar metabolism. Our study provides new insights into the molecular mechanisms driving the varying sucrose and fructose contents in ‘ZL’ and ‘LY’, highlighting several candidate structural genes and TFs that may play key roles in regulating sugar biosynthesis and distribution.