Genome-wide analysis of the WOX transcription factor family in Platycodon grandiflorus identifies PlgWOX2 as a regulator of shoot regeneration in Nicotiana benthamiana

Plant regeneration depends on the ability of differentiated cells to reprogram their developmental fate, yet the transcriptional regulators underlying this process remain incompletely understood in many species. The WUSCHEL-related homeobox (WOX) transcription factors are central components of plant developmental networks, but their roles in regeneration of medicinal plants such as Platycodon grandiflorus remain unclear. Here, we identified nine WOX genes in the P. grandiflorus genome and analyzed their phylogenetic relationships and expression patterns during hormone-induced redifferentiation. Expression profiling revealed distinct transcriptional patterns among PlgWOX members and hormone-responsive regulation of several genes. In particular, PlgWOX3 and PlgWOX5 were strongly induced by auxin treatment, while additional members were activated under combined auxin–cytokinin conditions. Functional analysis using transgenic Nicotiana benthamiana showed that PlgWOX2 overexpression accelerated shoot organogenesis, reducing the time required to reach 50% shoot regeneration from 15.2 days in wild-type explants to 14.1 and 13.6 days in two independent overexpression lines. PlgWOX2 -overexpressing lines exhibited elevated basal expression of CLAVATA3a, a marker associated with shoot meristem identity, although this difference diminished during regeneration, suggesting a potential role of PlgWOX2 in the early phase of shoot regeneration. These findings identify PlgWOX2 as a candidate regulator associated with early regenerative competence in P. grandiflorus based on heterologous functional analysis in N. benthamiana . This study provides the first comprehensive characterization of the WOX transcription factor family in P. grandiflorus and establishes a framework for understanding WOX-mediated transcriptional regulation of regeneration in medicinal plants.