Building Hovenia dulcis pseudofruit quality from proteomic and metabolomic perspectives

Hovenia dulcis Thunb. (Japanese grape tree) pseudofruit exhibits a period of growth of 180 days, with maturation initiated between 120 and 150 days after anthesis (DAA). Effective ripening occurs 150 DAA, characterized by intense softening, pectic solubilization and starch-sugar conversion. Multi-omic analysis identified 496 proteins, with 222 being differentially expressed. Significant highlights included energy metabolism (Malate Dehydrogenases, Glyceraldehyde-3-phosphate Dehydrogenase, Pyruvate Kinase) and photosynthetic pathways (Ribulose-1,5-bisphosphate Carboxylase/Oxygenase, Photosystems I and II), indicating that ripening demands a high energy supply. Multivariate analysis stratified the development into three phases: chemical defense (S1-S2), metabolic transition (S3-S6), and sensory ripening (S7). The Variable Importance in Projection (VIP) score and Principal Component 1 (PC1) loadings confirmed that the transition is governed by changes in volatile compounds (2-heptanol), respiratory physiology, density, and Hue angle, with a central role for malate dehydrogenase. Pearson correlations revealed a coordinated system in which central metabolism (Glyceraldehyde-3-phosphate Dehydrogenase, Triose Phosphate Isomerase) is coupled with ethylene signaling (S-adenosylmethionine Synthetase) and antioxidant defenses (Superoxide Dismutase, Catalase, and Peroxiredoxin 2). It is concluded that H. dulcis development is sustained by a strategic proteometabolic network that redirects the investment from protective biomolecules toward the specialization of sensory attributes, defining the final quality of the pseudofruit.