WD40 Gene Family in <i>Paulownia</i> : Genome-Wide Identification, Stress Regulation, and Pathogen Effector Interactions

WD40 proteins are key regulators of defensive metabolism and stress adaptation, promising targets for engineering stress-tolerant woody species. Through genome-wide analysis, we identified 231 PfWD40 genes in Paulownia fortunei, establishing the first WD40 genomic resource in Paulowniaceae and revealing its domain architectures and expansion patterns. Expression profiling showed 32, 67, and 76 PfWD40 genes differentially expressed under salt, drought, and phytoplasma stress, respectively. PfWD40-98 and PfWD40-116 interact with the WRKY protein PfTG21 and modulate flavonoid biosynthesis. Importantly, we provide the first evidence that phytoplasma effectors (Pawb3, Pawb19, Pawb51) directly target these regulatory PfWD40 proteins, validated by Y2H and BiFC assays. Molecular docking identified key residues governing these interfaces. This study establishes the first WD40 genomic resource in Paulownia and reveals a previously unreported pathogenic strategy─effector-mediated hijacking of a host WD40 hub─offering molecular insights for developing stress-tolerant and disease-resistant woody plants.