A Novel In Vitro Regeneration System Reveals Tissue-Specific Dynamics of Wound Repair in Poplar Stems

Plants are prone to injury in nature, yet how woody stems repair damaged protective and vascular tissues remains poorly understood. We established an in vitro bridge-culture system in hybrid poplar to track regeneration after longitudinal stem cutting. Lignin deposition began in diverse cells beneath the wound by 2 days after cutting (DAC), marking an early wound response. Repair then followed distinct tissue-specific trajectories. In the cortex and secondary phloem, cell division generated callus-like tissue that covered the wound by 2–4 DAC. New phellogen subsequently formed beneath the callus and produced phelloderm and ligno-suberized phellem, forming a wound periderm resembling native periderm by 12 DAC. In vascular cambium and young phloem, cells expanded and proliferated to reconnect the wound by 4 DAC, while restoration of cambium- and phloem-associated gene expression by 8–12 DAC indicated vascular recovery. Auxin responses also differed between tissues. PtaDR5::GUS activity was transiently induced during periderm regeneration but persisted in vascular regions until vascular development resumed. Exogenous auxin promoted periderm regeneration but had little effect on vascular cell divisions, whereas inhibiting polar auxin transport impaired vascular wound closure. Thus, periderm and vascular tissues undergo coordinated yet distinct repair processes regulated by tissue-specific auxin responses and transport.