Proteomic mechanism of sugar and organic acid metabolism during Korla fragrant pear (Pyrus sinkiangensis Yü) fruit development

Korla fragrant pear (Pyrus sinkiangensis Yü) fruit development involves complex physiological and biochemical processes; however, few data are available at the proteomic and metabolomic levels, which would be helpful for understanding the molecular mechanisms of fruit and quality development. Here, Korla fragrant pear was investigated across three stages, namely, early development (5 weeks after flower blooming, WAF), middle development (10WAF), and near ripening (15WAF), via tandem mass tag (TMT) labeling technology and ultra-performance liquid chromatography‒tandem mass spectrometry (UPLC‒MS/MS). Through proteomic and metabolomic analyses, we identified a total of 8487 proteins expressed during pear fruit development, and 3762 differentially expressed proteins (DEPs) were characterized at three fruit development stages. Moreover, 27 soluble sugars and 43 organic acids were found to accumulate differentially in the fruit at different developmental stages. The expression of proteins related to sugar metabolism and accumulation increased with increasing fruit development stage, which was consistent with the trend in soluble sugar content during fruit development. All 6 disaccharides, including cellobiose (Cel), lactose (Lac), maltose (Mal), trehalose (Tre), phenylglucoside (Phe) and sucrose (Suc), detected in this study were present at low levels in the early stages of fruit development but accumulated in large amounts from 15 WAF to 20 WAF, which may explain the high sweetness of the ripe Korla fragrant pear. In addition, The low organic acid levels during fruit development may explain the low organic acid content of Korla fragrant pear. Thus, our proteomic and metabolomic analyses reveal the molecular basis for the high sweetness and the low organic acidity of Korla fragrant pears.