The SBP-box transcription factor PlSPL2 negatively regulates stem development in herbaceous peony.

Key message: The SBP-box transcription factor PlSPL2 silencing in herbaceous peony enhanced stem strength by regulating xylem development, whereas its overexpression in tobacco resulted in weaker stem strength and undeveloped xylem. The strength of plant stems is a critical determinant of lodging resistance of plants, which significantly affects crop yield and cut-flower quality. Squamosa promoter binding (SBP) protein-like (SPL) transcription factors (TFs), participate in multiple regulatory processes, particularly in stem development. In this study, PlSPL2, an orthologous gene of Arabidopsis AtSPL2 in herbaceous peony, was isolated and found to contain a conserved SBP domain featuring two typical Zn-binding sites, as well as a nuclear localization sequence (NLS). Subsequently, transient infection of tobacco leaf epidermal cells using Agrobacterium confirmed the nuclear localization of PISPL2 protein. Additionally, gene expression analyses revealed that PlSPL2 was preferentially expressed in stems, and demonstrated a download trend in expression levels within vascular bundles during stem cell wall development. Furthermore, silencing of PlSPL2 in herbaceous peony enhanced stem strength. The silenced plants exhibited more developed xylems with wider radii and higher numbers of cell layers. Overexpression of PlSPL2 in tobacco, however, resulted in weaker stem strength, accompanied by a narrower radius of the xylem. These findings suggested that PlSPL2 was a negative regulator of herbaceous peony stem development, and its discovery and research could significantly contribute to a deeper understanding of stem growth and development mechanisms.