FaWRKY21 Enhances Postharvest Resistance to Botrytis cinerea in Strawberry by Activating Jasmonic Acid Biosynthesis.

Strawberry (Fragaria × ananassa) is highly susceptible to gray mold caused by Botrytis cinerea. WRKY transcription factors and jasmonic acid (JA) are central to defense against necrotrophs, yet the regulatory interaction in strawberry remains unclear. Here, we characterized FaWRKY21, a terpinen-4-ol-responsive, Group IIc WRKY gene encoding a nuclear-localized protein. Transient overexpression in strawberry fruit enhanced defense against B. cinerea and increased endogenous JA concentrations. This enhanced defense was confirmed in transgenic Arabidopsis plants overexpressing FaWRKY21, where AtPDF1.2 and other defense markers were upregulated. Transcriptomic and qRT-PCR analyses revealed that FaWRKY21 upregulates JA biosynthetic genes, notably FaOPR3II, FaJMT, and FaAOS-C. Yeast one-hybrid, EMSA, and dual-luciferase assays demonstrated direct binding to W-box elements in their promoters and transcriptional activation. Our findings establish FaWRKY21 as a direct activator of JA biosynthesis that positively regulates defense against B. cinerea, offering molecular targets for developing elicitor-based strategies to control postharvest gray mold.