Gibberellin modulates the post-transcriptional regulation of CsHDZ34 to positively regulate bud break in tea plants

Sprouting, an important process in plant growth and development, is economically critical for the tea plant (Camellia sinensis (L.) O. Kuntze) and other horticultural crops, in which tender spring shoots constitute the primary harvest. While gibberellin's (GA) role in plant growth is well-established, its molecular control over bud sprouting and the underlying regulatory network remain incompletely characterized. This study employed electrophoretic mobility shift assay, dual-luciferase reporter assays, yeast one-/two-hybrid, and in situ hybridization to elucidate the transcriptional regulatory network among CsHDZ34, CsZHD9, CsDELLA5, and CsMADS27, while the functions of CsHDZ34 and CsDELLA5 in tea bud sprouting were investigated using western blotting, antisense oligodeoxynucleotides, gene overexpression, and data-independent acquisition quantitative proteomics, along with genome-wide association study analysis and high-throughput mutation detection to characterize their genetic variations. This study identified CsHDZ34 as an upstream regulator of CsZHD9, which promotes tea bud sprouting, and found that GA promoted alternative splicing in the 5' untranslated region of CsHDZ34, increasing its protein abundance in tea buds. The positive role of CsHDZ34 in bud break regulation was validated by ectopic expression in poplars and gene silencing in tea plants. CsDELLA5 was identified as being directly downstream of CsHDZ34 and as an interaction factor of CsMADS27. Notably, the CsDELLA5^Hap2 variant was identified as less susceptible to GA-mediated degradation, allowing it to accumulate and act as a transcriptional activator that interacts with CsMADS27, thereby promoting bud sprouting through direct regulation of downstream target genes. These findings reveal a novel molecular mechanism orchestrated by CsHDZ34 that promotes bud sprouting in tea plants through spliceosome modulation and GA signaling. This provides a theoretical framework for elucidating bud break mechanisms and advancing early cultivar breeding.