Brassinosteroid signaling drives floral transition defects in Camellia sinensis ‘Ziyang 1’ via CsBZR2-mediated suppression of CsFLC

The tea plant (Camellia sinensis) is an economically important leaf crop in which the flowering process consumes substantial nutrients, thereby negatively impacting tea yield and quality. Therefore, deciphering the molecular basis of floral transition is essential for enhancing tea cultivars and optimizing plantation management. The non-flowering tea plant line ‘Ziyang 1’ (ZY1H), which has failed to flower for several consecutive years, and the normal-flowering cultivar ‘Ziyang’ (ZYQT) were used to study the molecular mechanisms underlying the non-flowering phenotype in ZY1H. Phenotypically, ZY1H exhibited shortened internodes, prolonged vegetative growth, and failure to develop floral meristems. Chromosomal analysis confirmed that ZY1H maintains a normal diploid chromosome number (2n=30), excluding triploidy as a causal factor for its non-flowering trait. Transcriptome analysis revealed an impaired vegetative-to-reproductive transition in ZY1H, manifesting as low expression of SPL genes and sustained high expression of flower-repressive AP2-like genes. Additionally, elevated expression of the flowering repressor SVP and reduced expression of the floral integrator FT further disrupted the convergence of floral inductive signals. Notably, brassinosteroid (BR) levels and CsBZR2 expression were elevated in ZY1H. Functional assays showed that CsBZR2 directly binds the CsFLC promoter and suppresses its expression, thereby blocking the flowering process. Collectively, these results demonstrate that disrupted BR signaling and sustained vegetative growth jointly trigger the floral transition defect in ZY1H. This work provides novel insights into the molecular mechanisms of flowering regulation in tea plants and valuable theoretical support for cultivar improvement.