Comparative Physiological and Transcriptomic Analyses Revealed Key Metabolic Pathways Involved in Ethanol Fermentation in Nanguo Pears during Ripening.

Nanguo pears produce a distinctive "alcoholic taste" during ripening, while Jingbai pears do not. To better understand the regulatory mechanism of "alcohol taste" formation in Nanguo pears, differences in ethanol fermentation-related metabolisms between the two cultivars were investigated. Compared to Jingbai pears, Nanguo pears had higher activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) and contents of pyruvate, acetaldehyde, and ethanol during ripening. Nanguo pears generally showed higher starch degradation and higher levels of acetyl-CoA and citric acid but lower respiration rate and ATP levels. Transcriptome analysis revealed that starch-to-sugar conversion, glycolysis, tricarboxylic acid cycle, and pentose phosphate pathway might coregulate the ethanol metabolism of Nanguo pears. Additionally, the gene expression of PuBMY1, PuPDC1/2, PuADH5, PuHK3, PuPFK1/2/4, and PuG6PDH1/2 was positively correlated with ethanol content during the initial stage of ethanol accumulation in Nanguo pears. Our findings will help elucidate the regulatory network of "alcoholic taste" formation in Nanguo pears.