Genome-Wide Identification of the PP2A Gene Family in Strawberry (Fragaria × ananassa) and Pharmacological Evidence for the Involvement of PP2A in ALA-Mediated Salt Tolerance

Background: Protein phosphatase 2A (PP2A) is a conserved serine/threonine phosphatase that plays crucial roles in stress responses, yet its function in strawberry (Fragaria spp.) remains largely uncharacterized. This study aimed to characterize the PP2A gene family in octoploid strawberry and to investigate its involvement in ALA-induced salt tolerance. Methods: We identified PP2A genes in the octoploid strawberry ‘Benihoppe’ genome and classified them into scaffold (A), regulatory (B55, B56, B″), and catalytic (C) subunit families. Segmental duplication and selection pressure were analyzed using Ka/Ks. Time-course RNA-seq was performed under NaCl and ALA treatments. Physiological assays measured SOD and CAT activities, O2•− and MDA accumulation, and PP2A activity. Cantharidin was used to pharmacologically inhibit PP2A. Results: Seventy-five PP2A genes were identified. Segmental duplication was the primary driver of PP2A family expansion (70/75 genes), with all duplicated pairs under strong purifying selection (mean Ka/Ks = 0.138). Time-course RNA-seq analysed with DESeq2 identified three B56-subfamily PP2A genes as differentially expressed between NaCl and NaCl + ALA at 24 h (FDR < 0.05), the most strongly affected being FaPP2AB′η-5; in contrast, several C4 catalytic subunits were suppressed by salt stress. This ALA-responsive induction declined sharply at 48 h and 72 h. Physiological assays demonstrated that ALA significantly enhanced SOD and CAT activities while reducing O2•− and MDA accumulation under NaCl stress, and ALA also elevated PP2A activity. Cantharidin largely attenuated both the ALA-induced increase in PP2A activity and ALA-mediated antioxidant protection. Conclusions: This study provides a comprehensive characterization of the strawberry PP2A gene family and indicates that PP2A activity contributes to ALA-induced salt tolerance, revealing a functional link between ALA signaling and PP2A-mediated antioxidant defense.