PpMYB14-SAHH1 Module Regulates Peach Fruit Softening Through Promoting Lignin Accumulation

Fruit softening critically impacts postharvest quality and storage of peach (Prunus persica L.). To explore the molecular mechanism regulating postharvest peach softening and identify key genes for maintaining fruit quality, this study focused on investigating the function and regulatory network of S-adenosine-L-homocysteine hydrolase 1 (SAHH1). Postharvest peach fruits showed continuous firmness decline and significant anthocyanin accumulation after day 10, indicating a rapid softening initiation. qRT-PCR confirmed PpSAHH1 was strongly positively correlated with firmness (r = 0.648). PpSAHH1 overexpression in peach delayed senescence by maintaining firmness, retarding color change, and preserving cell membrane integrity, while heterologous expression in tomato regulated ripening. Bioinformatics revealed PpSAHH1 is a cytoplasmic acidic soluble protein with conserved structures, evolutionarily close to Prunus dulcis SAHH, and its promoter contains abscisic acid (ABA)-responsive elements. Stable overexpression in apple callus altered cell wall metabolism: reduced pectin and increased cellulose, hemicellulose, and lignin. Transcriptome analysis showed differentially expressed genes enriched in phenylpropanoid biosynthesis, calcium/auxin/ABA signaling, and plant-pathogen interaction. Yeast one-hybrid, dual-luciferase, and GUS assays verified myeloblastosis transcription factor 14 (PpMYB14) directly binds the PpSAHH1 promoter and activates its transcription. Silencing of MdMYB14 in apple significantly reduced the accumulation of total phenols and cell wall metabolic components, particularly lignin content. Collectively, the PpMYB14-SAHH1 module inhibits peach softening by coordinately regulating multiple signaling pathways and phenylpropanoid biosynthesis to promote lignin accumulation, offering new insights and potential targets for postharvest quality improvement.