Integrative Analysis of Transcriptome and Metabolome Reveals the Light Quality-mediated Regulation of Adventitious Shoot Proliferation in Chinese Fir

Chinese fir (Cunninghamia lanceolata) is an important fast-growing tree species for timber production and ecological protection in China. Tissue culture is a key method for fast-propagating Chinese fir seedlings, but the technique is hindered by low proliferation rate and poor seedling quality. Light quality plays a crucial role in influencing seedling proliferation and growth, but the underlying regulatory mechanisms remain poorly understood. This study integrated transcriptome and metabolome analyses to investigate how light qualities regulate adventitious shoot proliferation and growth in tissue-cultured Chinese fir seedlings. Seedlings were grown under red, green, blue, and composite light-emitting diode (LED) conditions, with white light serving as the control. The results showed that blue light and blue-dominant composite light significantly enhanced adventitious shoot proliferation by promoting higher levels of auxin (IAA) and cytokinin (CTK), with gibberellin (GA) strongly enhancing the proliferation under blue light. These light conditions also enhanced chlorophyll content and photosynthetic efficiency, thereby promoting biomass accumulation, and highlighting the significant regulatory effects of light quality on growth. In contrast, red light promoted shoot height, leaf area, and carotenoid content, likely due to elevated GA and reduced IAA and CTK levels but inhibited proliferation due to hormonal imbalances. Green light increased abscisic acid (ABA) levels, counteracting the proliferation-promoting effect of zeatin riboside (ZR) and suppressing shoot growth. Transcriptome and metabolome analyses identified key pathways involved in light quality-mediated regulation, including plant hormone signal transduction, photosynthesis, and flavonoid and carotenoid biosynthesis. Weighted gene co-expression network analysis (WGCNA) identified four key genes regulated by light quality that further modulated hormone biosynthesis and signaling transduction. The genes PSBS (encoding photosystem II protein) and FTSH (encoding cell division protease) were crucial for photosynthesis, proliferation, and biomass accumulation. GID1 (encoding gibberellin receptor) was essential for shoot height and leaf area expansion, and GST (encoding glutathione S-transferase) played a key role in carotenoid biosynthesis and stress tolerance of adventitious shoots. Differential expression of GA- and CTK-related genes, such as GID1, DELLA (GA negative regulator), B-ARR and A-ARR (Arabidopsis response regulators), underscored the pivotal role of light quality in regulating hormonal pathways. This research provided valuable insights for optimizing Chinese fir seedling proliferation and growth, and would ultimately contribute to sustainable plantation management.