PtrbZIP3 transcription factor regulates drought tolerance of Populus trichocarpa

Plant basic leucine zipper (bZIP) proteins participate in plant development and a variety of abiotic stress responses. However, their roles in response to abiotic stress in Populus are still unclear. In this study, we characterized a bZIP protein, PtrbZIP3, in Populus trichocarpa which belongs to the sub-family A. PtrbZIP3 expression was highly induced by treatment with NaCl, PEG6000, or abscisic acid (ABA). PtrbZIP3 is a nuclear protein with transcriptional activation activity. Yeast one hybrid and electrophoretic mobility shift analysis showed that PtrbZIP3 can specifically bind to abscisic acid-responsive element (ABRE) to regulate the expression of ABA-dependent genes and increase the amount of ABA in P. trichocarpa overexpressing PtrbZIP3. Under PEG-simulated drought conditions, overexpression of PtrbZIP3 increases the activities of antioxidant enzymes, scavenging of reactive oxygen species, maintains cell membrane integrity, reduces stomatal apertures and water loss, and increases proline accumulation. Thus PtrbZIP3 is a transcriptional activator that plays a role in an ABA-dependent pathway to improve osmotic tolerance in P. trichocarpa.