How poplar trees activate molecular shields against water loss
image: Schematic diagram of PtrbZIP12 regulating the drought resistance mechanism of P. trichocarpa.
Credit: Horticulture Research
Drought is one of the most damaging environmental stresses facing forests, but the genetic switches that help trees withstand water shortage remain only partly understood. A new study identifies PtrbZIP12 as a key regulator of drought resistance in Populus trichocarpa, a model tree species widely used in forest biology. By generating poplar plants with increased or disrupted PtrbZIP12 expression, researchers showed that this gene strengthens drought tolerance by improving reactive oxygen species (ROS) scavenging, boosting proline accumulation, reducing membrane damage, and limiting cell injury. The findings reveal a layered defense system that connects drought-responsive gene regulation, protein interaction, and phosphorylation.
Forests are increasingly exposed to prolonged and intense drought under climate change, threatening tree growth, wood production, carbon sequestration, and ecosystem stability. Trees cannot escape stress, and their long life cycles require durable systems for sensing and responding to water deficit. Plants rely on antioxidant enzymes, osmotic adjustment, hormone signaling, and transcription factors (TFs) to survive drought, but how these defenses are coordinated in woody species remains unclear. The basic leucine zipper (bZIP) family is known to regulate stress responses, yet S-subfamily bZIP members are still poorly characterized in trees. Due to these challenges, deeper investigation is needed into how drought-responsive transcription factors coordinate protective pathways in forest trees.
Researchers from the State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, China, reported (DOI: 10.1093/hr/uhag034) the findings in Horticulture Research on February 5, 2026. The article focuses on how PtrbZIP12 regulates drought adaptation in poplar. The study combines transgenic plant analysis, physiological assays, transcriptome profiling, protein-interaction tests, and promoter-activation experiments to define a drought-resistance module in a woody plant.
The team first found that PtrbZIP12 was strongly induced by drought-like stress and that the PtrbZIP12 protein was localized in the nucleus, consistent with its function as a transcription factor. Poplars overexpressing PtrbZIP12 showed less leaf damage, higher chlorophyll content, greater fresh weight, and better growth after water withholding than wild-type plants. In contrast, CRISPR-associated protein 9 genome editing (CRISPR/Cas9)-generated ptrbzip12 mutant lines were more drought sensitive. Physiological tests showed that PtrbZIP12 overexpression reduced malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide anion (O₂•⁻) accumulation, while increasing the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). The overexpression lines also accumulated more proline, an osmoprotective compound that helps cells maintain stability under water deficit. RNA sequencing (RNA-seq) identified PtrDHN, encoding a dehydrin, and PtrPOD, encoding a peroxidase, as major downstream targets. Multiple molecular assays, including chromatin immunoprecipitation-polymerase chain reaction (ChIP-PCR), yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), and dual-luciferase (dual-LUC) tests, confirmed that PtrbZIP12 directly binds to and activates these two genes.
The authors said the results show that drought tolerance in poplar is controlled by an integrated regulatory module rather than by a single protective response. They said PtrbZIP12 acts as an upstream switch that turns on genes linked to antioxidant protection and cellular stability, while also working with other proteins to strengthen the drought-response signal. This helps explain how trees convert water-deficit stress into coordinated molecular and physiological defenses.
The study further shows that PtrbZIP12 interacts with PtrbZIP3, another drought-related bZIP transcription factor, and the two proteins jointly enhance activation of PtrDHN and PtrPOD. PtrSnRK2 also phosphorylates PtrbZIP12, increasing its ability to activate these downstream targets. This multilayered mechanism suggests that improving drought tolerance in trees may require tuning regulatory networks, not only individual genes. The PtrSnRK2–PtrbZIP12–PtrDHN/PtrPOD pathway may support future breeding and biotechnology strategies aimed at developing drought-resilient poplar varieties and strengthening forest adaptation to climate change.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhag034
Funding information
This study was financially supported by the National Natural Science Foundation of China (Grant No. 32401600) and the National Key Research and Development Program of China (2016YFD0600106).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.