BZR1 targets steroid 22-alpha hydroxylase 4 to negatively regulates cell elongation in bamboo

Moso bamboo is renowned for its exceptional growth rate, driven by rapid cell proliferation and elongation in culm internodes. This study uncovers the novel role of brassinosteroids (BRs) in regulating bamboo shoot growth, revealing a previously unknown negative correlation between BR levels and growth rates. Notably, we identify BRASSINAZOLE RESISTANT1 (BZR1) acts as a key transcription factor in BR signaling, governing the expression of genes involved in BR biosynthesis and growth. Specifically, we elucidate the interactions between PeBZR1s and the promoter of steroid 22-alpha hydroxylase gene (PeDWF4) encoding a critical enzyme of BR metabolism. Our findings show that the transcriptional expression levels of PeBZR1-4, PeBZR1-5, and PeBZR1-7 positively correlated with BRs content. Furthermore, all three can bind to the BRRE motif on the PeDWF4 gene promoter, thereby suppressing PeDWF4 expression. Additionally, we demonstration that knockdown of PeDWF4 in bamboo through planta gene editing results in shorter epidermal cells and reduced expression of cell elongation genes. Conversely, Arabidopsis overexpressing PeDWF4 exhibited enhanced cell elongation and larger leaves. These findings reveal PeBZR1-4, PeBZR1-5, and PeBZR1-7 as negative regulators of cell elongation through PeDWF4 inhibition. This discovery not only advances our understanding of BR-mediated regulatory mechanisms underlying the rapid growth of bamboo but also opens new approaches for future research, particularly in applying these insights to develop innovative strategies in bamboo targeted breeding and biotechnology to optimize growth characteristics.