PlLBD36 contributes to stem development through interacting with PlNF-YA1 to regulate <i>PlEXPA15</i> expression in herbaceous peony

Stems play a crucial role in the growth and survival of plants. Previous studies have implicated expansins (EXPs) in stem development, but the upstream regulatory mechanisms related to this process remain unclear. In this study, we identified an α-expansin subfamily gene PlEXPA15 as being highly expressed in the stems of herbaceous peony (Paeonia lactiflora Pall.) and localized to the cell wall. Further investigations revealed that PlEXPA15 could promote stem development by facilitating cortex cell expansion and secondary xylem development in P. lactiflora. Moreover, we identified the LBD transcription factor PlLBD36 as a potential regulator of PlEXPA15 through yeast one-hybrid screening, specifically through binding to the typical G-box element in the PlEXPA15 promoter and activating its transcription. PlLBD36 was also highly expressed in stems, and its protein localized in the nucleus. Silencing of PlLBD36 in P. lactiflora inhibited stem development by suppressing cortex cell expansion and secondary xylem development. Furthermore, yeast two-hybrid screening identified PlNF-YA1, a nuclear-localized NF-YA transcription factor, as an interacting partner of PlLBD36 that also positively regulates stem development by affecting cortex cell expansion and secondary xylem development. Additionally, the interaction between PlNF-YA1 and PlLBD36 promoted the transcriptional activation of PlLBD36 on PlEXPA15. Collectively, these findings demonstrate that the PlNF-YA1/PlLBD36-PlEXPA15 transcriptional cascade positively contributes to stem development through promoting cortex cell expansion and secondary xylem development in P. lactiflora, which provides insights into the molecular mechanisms underlying plant stem development.