UV-B promotes flavonoid synthesis in Ginkgo biloba leaves

摘要

Ultraviolet-B (UV-B) radiation is a natural source of environmental stress for plants. Notably, plants have evolved various protective mechanisms to combat the detrimental effects of UV-B exposure, including the production of UV-absorbing flavonoid compounds. Flavonoids are pharmaceutical active substances in Ginkgo biloba extracts. To clarify the molecular mechanisms underlying UV-B tolerance in G. biloba, we determined the flavonol composition and transcriptomic profile of G. biloba leaves after long-term UV-B exposure. Using high performance liquid chromatography and mass spectroscopy, we observed significant accumulation of flavonols in G. biloba leaves after UV-B exposure. In particular, isorhamnetin increased more than 16-fold. Combined transcriptome data with quantitative real-time polymerase chain reaction, structural genes involved in flavonoid synthesis were identified to be up-regulated expression after UV-B exposure. Particularly, the expression of FLS (Gb_22751) and F3'H (Gb_19792, Gb_04545, and Gb_11520) increased significantly, indicating their important roles in flavonoid synthesis response to long-term UV-B radiation. In addition, we found bZIP transcription factor (TF) Gb_12012 (encoding elongated hypocotyl-5, HY5) and MYB TFs (Gb_38090) were up-regulated, while MYB TFs (Gb_18153, Gb_40629, and Gb_05115) were down-regulated. We further identified two UV-B signalling molecules, including UVR8 (Gb_14008) and constitutive photomorphogenic-1 (COP1, Gb_15627) in G. biloba. These results suggest that the enhanced long-term UV-B radiation could promote flavonoid biosynthesis and metabolism, which is beneficial for the accumulation of medically active ingredients in G. biloba leaves.