CsBADH-mediated glycine betaine biosynthesis confers drought tolerance in tea plants

Drought stress severely constrains global tea production. Exogenous glycine betaine (GB) application significantly enhances drought tolerance in tea plants ( Camellia sinensis ), with a markedly stronger effect in drought-sensitive cultivars than in tolerant ones. Through genome-wide ALDH family analysis, we identified CsBADH as the sole functional betaine aldehyde dehydrogenase responsible for GB biosynthesis in tea, and recombinant enzyme assays confirmed its catalytic activity. Drought stress induced CsBADH expression, and its functional importance was confirmed through heterologous overexpression in Arabidopsis and tobacco, as well as through transient overexpression and antisense oligonucleotide-mediated silencing in tea plants. Collectively, these experiments demonstrated that CsBADH is required for drought-induced GB accumulation and tolerance. Mechanistically, CsBADH overexpression reduced oxidative damage and maintained cellular osmotic homeostasis, as evidenced by decreased malondialdehyde (MDA) accumulation, elevated proline content and peroxidase (POD) activity, and preserved photosynthetic efficiency (Fv/Fm). Importantly, foliar GB application did not significantly alter the catechin quality index (CQI) in fresh leaves, as determined by UPLC, nor did it adversely affect tea volatile profiles or organoleptic quality, as confirmed by electronic nose and sensory evaluations. Collectively, these findings establish CsBADH -mediated GB biosynthesis as a critical drought-tolerant mechanism in tea and support exogenous GB application as an effective, safe, and quality-preserving strategy to mitigate drought damage, particularly in drought-sensitive cultivars.