Transcriptome Analysis Reveals Distinct Differences in Organic Acid Metabolism Between the Pericarp and the Pulp of <i>Cerasus humilis</i> During Fruit Maturation

Organic acids are key components that determine the taste and flavor of fruits, playing a crucial role in maintaining fruit quality and nutritional value. To investigate the metabolic differences of organic acids between the fruit pericarp and the pulp during the developmental maturation of the <i>Cerasus humilis</i>, this experiment utilized <i>Cerasus humilis</i> cultivated in Inner Mongolia, China, as the experimental material. By measuring the malic acid and citric acid content, as well as the activities of the related metabolic enzymes in the fruit pericarp and the pulp at five developmental stages, this study investigated the characteristics of organic acid accumulation, changes in enzyme activities, and the expression trends of corresponding genes. Transcriptomic data were integrated to support the analysis. This study specifically analyzed the reasons for the differences in acidity between the pericarp and the pulp, and performed a correlation analysis of various indicators. The results indicated that, during development, the organic acid composition in both the pericarp and the pulp was primarily malic acid, with citric acid as a secondary component. The malic acid and citric acid content in the pericarp were significantly higher than in the pulp, resulting in greater overall acidity in the pericarp. The combined action of PEPC, NAD-MDH, and NADP-ME was identified as the primary reason for the differences in malic acid content between the pericarp and the pulp of <i>Cerasus humilis</i>. CS and ACO were identified as the key enzymes responsible for the lower citric acid content in the pulp compared to the pericarp. Furthermore, the expression levels of <i>ChMDH2</i>, <i>ChME</i>, <i>ChCS2</i>, <i>ChCS3</i>, <i>ChACO1</i>, and <i>ChACO2</i> differed significantly between the fruit pericarp and the pulp, suggesting their regulatory roles in organic acid accumulation.