Enhancement of cold tolerance in tea plants (Camellia sinensis) by glycine betaine accumulation through CsBADH overexpression

Cold stress significantly limits the growth and yield of tea plants (Camellia sinensis (L.) O. Kuntze), particularly in northern China, may lead to huge economic losses. Glycine betaine (GB), an osmotic regulator, is widely applied in crop resistance to abiotic stress. This study investigates the role of GB and its biosynthetic enzyme CsBADH in enhancing cold tolerance in tea plants. Two cultivars, 'Shuchazao' (cold-resistant) and 'Baiye 1' (cold-sensitive), were subjected to low temperature stress (0 °C). GB accumulation was measured, revealing that 'Shuchazao' exhibited 1.4-fold higher GB levels than 'Baiye 1', suggesting a link between higher GB accumulation and cold tolerance. Exogenous GB treatment improved cold resistance, especially in the cold-sensitive cultivar 'Baiye 1'. The CsBADH gene, a key enzyme in GB biosynthesis, was cloned and expressed in Escherichia coli, confirming its activity. Transgenic Arabidopsis thaliana, Nicotiana tabacum, and C. sinensis plants overexpressing CsBADH showed increased GB levels (1.5- to 2.4-fold), proline content, peroxidase (POD) activities, and enhanced cold tolerance, while silencing CsBADH decreased GB accumulation and cold resistance. These findings demonstrate that CsBADH plays a critical role in cold stress response by promoting GB accumulation, offering potential strategies for improving the resilience of tea and other leaf crops to cold stress.