PdbMYB44 enhances drought tolerance via PP2C-mediated modulation of ABA signaling and stomatal aperture

PdbMYB44, an R2R3-type MYB transcription factor (TF), responds to drought stress, yet its mechanism in conferring drought tolerance remains unclear. In the present study, we characterized PdbMYB44, an R2R3-MYB TF from Shanxin poplar (Populus davidiana × P. bolleana). The expression of PdbMYB44 was induced by drought stress, and its overexpression significantly enhanced drought tolerance, promoting root growth, increasing the root-to-shoot ratio, and improving antioxidant capacity. RNA-seq analysis revealed that PdbMYB44 differentially regulates key ABA signaling genes, including PYR1 and PP2Cs. Furthermore, yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) assays all confirmed that PdbMYB44 directly binds to the MBS and G-Box motifs in the promoters of ABA signaling repressors PP2Cs (PP2C75, PP2C51-2, PP2C24, and PP2C51-1) to inhibit their transcription. By repressing PP2C transcription, PdbMYB44 relieves the inhibition of SnRK2.6, thereby promoting its autophosphorylation and activation. The activated SnRK2.6 in turn phosphorylates SLAC1. Consequently, this PdbMYB44-initiated signaling cascade accelerates stomatal closure and significantly reduces leaf water loss in the overexpression lines compared to wild-type plants. Collectively, these findings elucidate a regulatory mechanism by which PdbMYB44 enhances drought tolerance through ABA-mediated stomatal closure, providing insights and a potential genetic resource for improving drought resistance.