UV-B Stress Regulates the Transcription of UVR8 Signal System-Related Gene and the Synthesis of Isoflavones in Soybean Sprouts

Abstract

UV-B treatment can promote the accumulation of isoflavones in soybeans. This study investigated the possible medium-wave ultraviolet (UV-B) photoreceptor genes in soybeans and the relationship between the UVR8 signaling system and isoflavones synthesis by designing three germination modes. All predicted GmUVR8 were classified into 10 classes (A–J) based on phylogenetic affinities. Isoflavone biosynthesis genes comprising GmCHS, GmCHR1, GmCHI1A, GmCHI1B, GmCHI4A, GmIFS1, and GmIFS2 were activated in response to UV-B treatment, while the corresponding enzyme activities were stably maintained at high levels. The accumulation of total isoflavones was proportional to the time, regardless of the germination pattern. UV-B treatment promoted the accumulation of isoflavones more than white light treatment and the accumulation of all isoflavones except glycitin was promoted by UV-B. The total isoflavones content of soybean sprouts reached a peak under the irradiation intensity of 45 μW/cm² under different irradiation intensities, which increased by 72.65% compared with that in the dark group. Furthermore, the correlation analysis showed that GmUVR8-E, GmUVR8-F₁, GmUVR8-J_1~3, GmUVR8-J₄, and GmUVR8-J_5,6 were highly correlated with isoflavones synthesis and might regulate the transcription of isoflavones synthesis gene, presumed as photoreceptor of UV-B in soybean. The results will provide a scientific basis for developing soybean foods rich in isoflavones.

Graphical abstract