Abstract
Apples from high-altitude orchards exhibit a distinctive sugar-acid balance, yet the varietal and maturity drivers remain unclear. A multi-omics survey was conducted to map sugars and acids and to resolve pathway control. Chromatography-mass spectrometry, RNA-seq, and principal component (PC) dimensionality reduction fitting analysis were integrated across Malus prunifolia and M. asiatica at 60 and 120 days after flowering (DAF). PC separated maturity on PC1 and species on PC2, and canonical correlation confirmed gene-metabolite couplings. Malate predominated but declined with ripening as sucrose rose; M. prunifolia at 60 DAF showed higher maltose/inositol, whereas M. asiatica at 120 DAF accumulated pentoses/xylitol. In M. prunifolia 60 vs. 120 DAF (Q60-Q120), enrichment targeted starch/sucrose plus pentose-glucuronate remodeling; in M. asiatica 60 vs. 120 DAF (S60-S120), fructose/mannose routes dominated with persistent wall-sugar signatures. Correlations linked succinate and pyruvate positively, and malate negatively, to hexoses, outlining an ALMT9/MDH-bridged acid-sugar switch. These maturation-anchored markers inform quality breeding and postharvest strategies.