Exogenous phytohormone application and transcriptome analysis provides insights for adventitious root formation in Taxus cuspidata S. et Z

Taxus cuspidata S. et Z is a perennial tree with significant economic and medicinal values. T. cuspidata propagation using cuttings is one of the most efficient approaches to solve its propagation material production on a larger scale. Its adventitious roots play a crucial role in the hardwood cutting propagation. To understand the molecular mechanisms involved in T. cuspidata adventitious root development and thus improve the effectiveness of propagation techniques, we investigated the optimal exogenous hormone applications that can rapidly induce adventitious roots in T. cuspidata hardwood cuttings. The best rooting responses were observed in cuttings treated with indole butyric acid (IBA). Moreover, biochemical and molecular profiling analyses of cuttings treated with different IBA concentrations were carried out. Peroxidase and polyphenol oxidase activities consistently increased with IBA concentration increase, except for a decrease observed at IBA150. Indole-3-acetic acid, gibberellin, and ethylene concentrations were significantly higher in all IBA-treated samples compared with the control group. Comparative transcriptome analysis revealed thousands of differentially expressed genes among the four samples (IBA0, IBA50, IBA100, and IBA150) evaluated. Most differentially expressed genes were assigned to phytohormone signaling pathways and sugar metabolism. The AP2/ERF, bHLH, and MYB transcription factor families and genes involved in root development and cell division were also overrepresented during adventitious root formation. This study provides insights into establishing improved asexual propagation protocols and elucidating into the molecular mechanisms underlying root development in T. cuspidata hardwood cuttings.