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

1. The non-flowering tea mutant ZY1H provides a unique germplasm to explore floral induction mechanisms. 2. CsBZR2-mediated repression of CsFLC and altered brassinosteroid signaling are implicated in disrupting floral transition in ZY1H. 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 natural mutant ‘Ziyang 1’ (ZY1H, which had not flowered for years) and its wild-type cultivar ‘Ziyang’ (ZYQT, normal flowering) 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 cause of its sterility. Transcriptome analysis revealed defective vegetative-to-reproductive transition in ZY1H, manifesting as insufficient expression of SPL genes and sustained high expression of flower-inhibiting AP2-like genes. Additionally, elevated expression of the flowering repressor SVP and reduced expression of the flowering integrator FT further disrupted the integration of floral induction signals. Notably, brassinosteroid (BR) levels and CsBZR2 expression were elevated in ZY1H. Functional assays showed that CsBZR2 directly interacts with the CsFLC promoter and suppresses its expression, thereby blocking the flowering process. These findings suggest that the floral transition defect in ZY1H is driven by dysregulated BR signaling and excessive vegetative growth, to provide novel insights into the molecular mechanisms of flowering regulation in tea plants and valuable theoretical support for cultivar improvement.