UV-B is an important environmental factor that differentially affects plant growth and secondary metabolites. The effects of supplemental ultraviolet-B (sUV-B) exposure (T1, 1.40 kJ·m
−2·day
−1; T2, 2.81 kJ·m
−2·day
−1; and T3, 5.62 kJ·m
−2·day
−1) on the growth biomass, physiological characteristics, and secondary metabolites were studied. Our results indicated that leaf thickness was significantly (
p < 0.05) reduced under T3 relative to the control (natural light exposure, CK); The contents of 6-BA and IAA were significantly reduced (
p < 0.05); and the contents of ABA, 10-deacetylbaccatin III, and baccatin III were significantly (
p < 0.05) increased under T1 and T2. The paclitaxel content was the highest (0.036 ± 0.0018 mg·g
−1) under T3. The cephalomannine content was significantly increased under T1.
Hmgr gene expression was upregulated under T1 and T3. The gene expressions of
Bapt and
Dbtnbt were significantly (
p < 0.05) upregulated under sUV-B exposure, and the gene expressions of
CoA,
Ts, and
Dbat were significantly (
p < 0.05) downregulated. A correlation analysis showed that the 6-BA content had a significantly (
p < 0.05) positive correlation with
Dbat gene expression. The IAA content had a significantly (
p < 0.05) positive correlation with the gene expression of
Hmgr,
CoA,
Ts, and
Dbtnbt. The ABA content had a significantly (
p < 0.05) positive correlation with
Bapt gene expression.
Dbat gene expression had a significantly (
p < 0.05) positive correlation with the 10-deacetylbaccatin content.
Hmgr gene expression was positively correlated with the contents of baccatin III and cephalomannine.
Bapt gene expression had a significantly (
p < 0.01) positive correlation with the paclitaxel content. A factor analysis showed that the accumulation of paclitaxel content was promoted under T2, which was helpful in clarifying the accumulation of taxane compounds after sUV-B exposure.
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