Integration of Axillary Meristem Development and Gibberellin Homeostasis by CjLAS Regulates Shoot Branching in Clerodendrum japonicum

Abstract

Branching architecture is a key agronomic and ornamental trait in woody plants; however, the molecular mechanisms coordinating hormone-mediated axillary bud formation and outgrowth remain largely unclear. Clerodendrum japonicum (Thunb.) Sweet is an important ornamental woody species with strong branching potential, but the regulatory network underlying its shoot branching has not been characterized. In this study, we investigated the regulatory basis of hormone-induced branching in Clerodendrum japonicum and identified a LATERAL SUPPRESSOR homolog, CjLAS, as a key candidate regulator. Combined application of gibberellic acid (GA3) and 6-benzyladenine (6-BA) significantly promoted axillary bud formation and outgrowth, accompanied by extensive transcriptional reprogramming. Transcriptome sequencing and weighted gene co-expression network analysis (WGCNA) revealed that CjLAS was closely associated with branching development and hormone-responsive pathways. Expression analysis showed that CjLAS expression increased during the progression of hormone-induced axillary bud development and branch formation. Ectopic overexpression of CjLAS in Arabidopsis thaliana enhanced shoot branching, confirming its conserved positive role in regulating plant architecture. Furthermore, overexpression of CjLAS repressed the gibberellin (GA) biosynthetic genes AtGA20ox2 and AtGA3ox2, induced the catabolic gene AtGA2ox6, and reduced the endogenous levels of bioactive GA1 and GA4. These findings suggest that CjLAS promotes shoot branching by integrating axillary meristem regulation with GA homeostasis. This study reveals an additional layer of LAS-mediated regulation linking meristem development and hormone homeostasis during shoot branching in woody plants and provides insights into the molecular regulation of plant architecture in C. japonicum.