Growth and flavonol accumulation of Ginkgo biloba leaves affected by red and blue light

Ginkgo biloba L. is an economically important tree species in China rich in resources. Flavonoids in their leaves have a high medicinal value. Research on improving the flavonoid yield of G. biloba leaves by regulating environmental factors has been widely conducted. However, the effect of light quality on G. biloba growth and flavonoid accumulation is not clear, and its molecular mechanism has not been reported. In this study, one-year-old ginkgo seedlings were used as experimental material. Three treatments of red, mixed (red:blue = 1:1), and blue light were set up using LED lamps. Using white light as the control, differences of G. biloba growth and flavonol accumulation under different light qualities were explored. The results showed that under red, mixed, and blue light, the petiole of G. biloba elongated, the leaf area decreased, and the leaves tended to be slender, which was not conducive to the accumulation of leaves. The blue light significantly increased the height of G. biloba seedlings. The net photosynthetic rate under blue light was relatively lower, the transpiration rate was lower in the treatment groups, the stomatal conductance decreased significantly under mixed light, and the change in intercellular CO2 concentration was not significant. RNA sequencing (RNA-seq) combined with quantitative real-time polymerase chain reaction (qRT-PCR) showed that the transcription factors (TFs) HY5 (Gb_12012) and MYB (Gb_39081) and structural genes CHS (Gb_20355), F3H (Gb_29563), and FLS (Gb_14028, Gb_14029, and Gb_14030) positively regulated the biosynthesis of flavonols, whereas MYB-related TFs (Gb_27262 and Gb_34639) played a negative regulatory role. Combined with the existing research and the results of this experiment, we preliminarily speculated the mechanism of G. biloba response to red and blue light quality. After G. biloba leaves were stimulated by red and blue light, the expression of Gb_12012 changed the abundance of HY5 and affected the expression levels of downstream MYB TFs. MYB directly binds to the promoters of the structural genes CHS, F3H, and FLS to regulate its expression to promote (or inhibit) the biosynthesis of flavonols. Finally, Mixed and blue light significantly increased the flavonol content in G. biloba leaves, while red light was the opposite. Blue light significantly increased the flavone yield of G. biloba leaves per plant (increased by 0.76 times) and its antioxidant capacity. This lays a foundation for applying light quality in the cultivation of G. biloba for leaf use.