Ectopic expression of LBD15 affects lateral branch development and secondary cell wall synthesis in Arabidopsis thaliana

Lateral organ boundaries domain (LBD)/ASL (AS2-like) genes encode plant–specific transcription factors and play important roles in plant growth and development. However, little information is available about the LBD15 gene in Arabidopsis. Here, the expression patterns of the LBD15 gene were evaluated and its physiological roles in Arabidopsis were investigated. The LBD15 gene was expressed at different levels in many tissues including shoots, stems, roots, flowers and siliques. The overexpression of LBD15 can activate the transcription of BOP1 and BOP2, which are critical to controlling lateral organ development and inflorescence architecture. In addition, our results indicate that SND1, which is a key regulator of secondary wall synthesis, can bind to specific SNBE elements of the LBD15 promoter to activate the expression of LBD15. Elevated expression of LBD15 was found to down-regulate the transcription of CesA4, CesA7, and CesA8, which encode cellulose synthesis of the secondary cell wall, and disrupt the secondary cell wall formation. In this way, LBD15 may be involved in regulating secondary cell wall synthesis during differentiation of xylem cells. The present study provides novel evidence that may facilitate understanding the signaling network of lateral branch development and secondary cell wall synthesis in Arabidopsis.