PtrbZIP12 improves drought resistance in <i>Populus trichocarpa</i> by directly targeting PtrDHN and PtrPOD

Abstract This research examines how the basic leucine zipper (bZIP) transcription factor (TF) influences drought stress responses in tree species, emphasizing its related regulatory pathways, and thus offering a theoretical framework for understanding drought response mechanisms regulated by the bZIP TF family. Specifically, we characterized the functional role of the S subfamily bZIP gene, PtrbZIP12, from Populus trichocarpa, by developing transgenic poplars that either overexpressed or knocked down of PtrbZIP12. The findings indicated that PtrbZIP12 markedly improved drought tolerance in transgenic plants by facilitating reactive oxygen species (ROS) scavenging, enhancing proline biosynthesis, and reducing plasma membrane peroxidation and cell death. To pinpoint PtrbZIP12’s downstream targets, RNA sequencing was performed, followed by chromatin immunoprecipitation-PCR (ChIP-PCR), yeast one-hybrid, and dual-luciferase assays. These analyses confirmed that PtrbZIP12 binds directly to the promoters of PtrDHN (Dehydrin) and PtrPOD (peroxidase), leading to the activation of their expression. Transgenic poplars overexpressing (OE) PtrDHN or PtrPOD were subsequently generated, and similar to PtrbZIP12, their OE conferred enhanced drought tolerance. Moreover, co-expression of PtrbZIP12 with PtrbZIP3 further elevated PtrDHN transcript levels, resulting in improved drought resilience in the PtrbZIP12 transgenic lines. Moreover, phosphorylation was identified as a key factor in boosting PtrbZIP12-mediated transcriptional regulation of PtrPOD and PtrDHN, underscoring the significance of post-translational modification in plant drought stress responses.