PlEF1B-PlGATA5 module enhances stem strength by promoting syringyl lignin deposition in herbaceous peony

Stem bending or lodging caused by insufficient stem strength limits plant production. Although syringyl lignin (S-lignin) plays a crucial role in the formation of stem strength, its transcriptional regulatory network remains poorly characterized. In this study, we identified a nuclear-localized transcriptional activator, PlGATA5, from herbaceous peony (Paeonia lactiflora Pall.) that directly binds the WGATAR motif in the promoter of laccase 15 (PlLAC15) and activates its transcription. Moreover, silencing PlGATA5 in P. lactiflora resulted in decreased stem strength due to reduced S-lignin deposition, whereas PlGATA5 overexpression enhanced stem strength through enhanced S-lignin deposition. As revealed by yeast two-hybrid, bimolecular fluorescence complementation, and luciferase complementation imaging assays, the translation elongation factor PlEF1B physically interacts with PlGATA5, leading to enhanced transcriptional activation of PlGATA5 on PlLAC15 promoter activity. Additionally, silencing PlEF1B in P. lactiflora indicated that PlEF1B positively regulates stem strength by affecting S-lignin deposition and xylem width. These data support that the PlEF1B-PlGATA5 module directly activates PlLAC15 expression to enhance stem strength by promoting S-lignin deposition in P. lactiflora and provide important insights into stem strength regulation.