PlTUB1 Negatively Regulates Stem Development by Modulating Microtubule Organization and Cellulose Deposition in Herbaceous Peony

Stem development determines plant architecture and mechanical support, directly affecting yield, lodging resistance, and ornamental quality. Microtubules are essential components of the plant cytoskeleton, but their role in stem development in herbaceous peony (Paeonia lactiflora Pall.) remains largely unexplored. Here, a β-tubulin gene, PlTUB1, was identified from P. lactiflora. Its coding sequence was 1353 bp in length, encoding a 450-amino-acid protein that localized to microtubules, and its transcript levels declined progressively during stem development. Transient virus-induced gene silencing of PlTUB1 in P. lactiflora, with a silencing efficiency of approximately 55%, enhanced stem development, with increased stem diameter, elevated cellulose accumulation, and thickened secondary walls. Given that cellulose deposition and secondary wall thickening were closely associated with cortical microtubule organization, the role of PlTUB1 in microtubule regulation was further examined. Heterologous overexpression of PlTUB1 in Arabidopsis thaliana disrupted transverse microtubule alignment, reduced cellulose deposition, and impaired secondary wall and xylem development, thereby confirming the mechanistic link between PlTUB1 and microtubule organization. Collectively, these findings demonstrated that PlTUB1 negatively regulates stem development by modulating microtubule organization and secondary wall deposition, providing new insights into the cytoskeletal regulation of stem development in P. lactiflora.