Metabolomics and transcriptomics reveal molecular mechanisms of anthocyanin accumulation in 'Nanhong' pear (Pyrus ussuriensis) peel at different temperatures

Abstract

The bright red hue of the 'Nanhong' pear's pericarp is a key sensory attribute, yet its susceptibility to discoloration at harvest poses challenges for maintaining its commercial appeal. This study, employs quality metrics, metabolomics, and transcriptomics to examine fruit quality and anthocyanin metabolism, along with gene expression involved in anthocyanin biosynthesis, under dark conditions at 0 °C, 10 °C, 20 °C, and 30 °C for up to 21 d. Findings indicate that 0 °C is optimal for long-term storage, while 10 °C is preferable for retail display. LC-MS/MS identified 42 anthocyanin metabolites cyanidin-3-O-galactoside (cya-3-O-gal) being the primary pigment in the pericarp. Discoloration was primarily associated with cyanidin-type and peonidin-type anthocyanins. Transcriptome analysis identified a large number of differentially expressed genes (DEGs) in different comparison groups, KEGG pathway analysis highlighted the significant enrichment of DEGs in phenylpropane and flavonoid metabolic pathways. Key genes in the anthocyanin synthesis pathway, including PuPAL, PuCHS, PuCHI, PuF3`H, PuANS, and PuDFR were markedly down-regulated at 20 °C and 30 °C. Transcription factors such as AP2/ERF, WRKY, MYB, NAC, C2H2, bHLH,and bZIP played an influential part in this process. The study also established that fruit senescence and high-temperature stress were the primary causes of pericarp discoloration at these temperatures. Consequently, identifying optimal storage conditions that preserve fruit quality, delay senescence, and sustain anthocyanin accumulation is crucial. In this study, storage at 10 °C demonstrated the most favorable outcomes for maintaining the pericarp's red color during the marketing period.