Physiological and molecular mechanisms underlying the deterioration of external quality in postharvest fresh lotus seed

Fresh lotus seeds quickly lose their external quality during postharvest storage, significantly reducing shelf-life and commercial value. However, the physiological and molecular mechanisms underlying this deterioration remain unclear. In this study, lotus seed pericarps stored at room temperature (25 ± 0.5 °C) for 96 h exhibited notable changes: firmness decreased by 69.1 %, brightness (L*) dropped from 83.25 to 59.67, relative water content (RWC) fell from 75.1 % to 36.4 %, and hemicellulose content decreased by 20.5 %. The browning index increased from 0 to 0.99, polyphenol oxidase (PPO) activity increased 2.3-fold, malondialdehyde (MDA) content rose 1.6-fold, and lignin and total flavonoids increased 1.2-fold and 1.3-fold, respectively. Abscisic acid (ABA) and the ethylene precursor 1-aminocyclopropanecarboxylic acid (ACC) showed dynamic changes throughout storage. RNA-sequencing identified 13,282 differentially expressed genes (DEGs) associated with energy metabolism, wax biosynthesis, and plant hormone signal transduction, with many ABA- and ethylene-related genes being significantly induced. Weighted gene co-expression network analysis (WGCNA) revealed an upregulated gene co-expression module that correlated with the observed phenotypic changes in the pericarp. In this module, we identified two PPO encoding genes, NnPPO2 and NnPPO3. The expression of these genes, along with their enzyme activity, was closely linked to the deterioration of external quality. Our findings provide valuable insights into the physiological and transcriptional changes in lotus seed pericarps during postharvest storage, offering a theoretical foundation for further research aimed at improving quality and extending shelf-life.