Regeneration establishment of Camellia taliensis unravels its adventitious bud development profile dynamically regulated by auxin-ethylene signaling

Camellia taliensis (W.W. Sm.) Melch. is a wild relative of the cultivated tea plant Camellia sinensis, primarily distributed in southwestern China, northern Myanmar, and Thailand. C. taliensis is regarded as a key Camellia species for elucidating the origin and domestication of the tea plant and as an important source of plant material for natural metabolite discovery. However, there are knowledge and technical gaps in effective regeneration and developmental profiling of C. taliensis. Here, we established an efficient in vitro system for regeneration of C. taliensis using stem segment explants. From bud sprouting to root formation, optimal culture media were determined for each stage: axillary bud induction (MS + 2.0 mg·L⁻¹ 6-Benzylaminopurine (6-BA) + 0.2 mg·L⁻¹ naphthaleneacetic acid (NAA)), adventitious bud proliferation (MS + 3.0 mg·L⁻¹ 6-BA + 0.1 mg·L⁻¹ NAA), adventitious bud stem elongation (MS + 0.5 mg·L⁻¹ 6-BA + 0.05 mg·L⁻¹ NAA + 1.0 mg·L⁻¹ gibberellic acid), and root induction (½ MS + 3.0 mg·L⁻¹ indole-3-butyric acid). Morphological and histological analyses showed that adventitious buds were significantly more elongated in the medium with NAA:6-BA = 1:30 than in the medium with NAA:6-BA = 1:10 after 7 and 14 days of post-treatment, suggesting an important role of adventitious bud development in C. taliensis regeneration. Furthermore, transcriptome analysis of adventitious buds treated with different NAA/6-BA concentration ratios revealed distinct gene expression dynamics, with differentially expressed genes significantly enriched in pathways associated with environmental responses, cell wall remodeling, and hormone signaling. In particular, numerous genes associated with auxin and ethylene signaling pathways exhibited temporal expression patterns in the presence of NAA:6-BA = 1:30. This study establishes an efficient strategy for regeneration and conservation of C. taliensis and provides new insight into the molecular basis of its adventitious bud development.