Alkalization and cell wall remodeling mark the fruit abscission zone maturation in table olive

Abscission zones mediate organ separation through coordinated changes in cell wall architecture and intercellular signaling. To elucidate mechanisms of fruit abscission zone (FAZ) transitions preceding fruit detachment in the non-climacteric fruit olive (Olea europaea), we integrated physiological, transcriptomic, and cellular analyses during natural maturation and after ethylene treatment. A mesocarp-subtraction RNA-seq strategy uncovered a FAZ-enriched module of 733 genes, representing core regulators of FAZ maturation. Induction of β-1,3-glucanase genes corresponded with elevated glucanase activity and callose depletion at plasmodesmata, indicating increased symplastic signaling required to initiate the abscission. A previously undocumented rise in cytoplasmic and apoplastic pH of the olive FAZ, coupled with reduction of low-methylesterified homogalacturonan, represents a hallmark of pH-dependent wall remodeling. Transcriptomic enrichment of transporters and pH-responsive wall-modifying enzymes positions pH homeostasis as a central regulator upstream of wall reconfiguration. Concurrent activation of pectate lyases and key phenylpropanoid pathway enzymes suggests a dual remodeling trajectory involving reduction of de-methylesterified pectin, which weakens intercellular cohesion, and localized lignin deposition, defining the separation boundary. Our findings establish a conserved molecular circuit that confers ethylene competence to the FAZ and a mechanistic framework in which symplastic connectivity, pH-driven enzymatic activation, and modulation of wall polymer chemistry orchestrate FAZ maturation and fruit detachment in table olive.