SWATH-based quantitative proteomic analysis of Morus alba L. leaves after exposure to ultraviolet-B radiation and incubation in the dark.

Morus alba is a woody shrub of the family Moraceae and used as traditional Chinese medicine for a long history. Ultraviolet-B (UV-B) radiation, as a kind of abiotic stress factor, affected the growth and secondary metabolism in M. alba. Previous studies indicated that the contents of several secondary metabolites such as moracin N, chalcomaricin were significantly increased under high level UV-B radiation and dark incubation in M. alba leaves. To reveal the response mechanism under UV-B radiation and dark incubation in M. alba leaves, SWATH-based quantitative proteomic analysis was performed. Totally, 716 proteins were identified and quantified in the control, UVB, and UVD groups. Among them, 123 proteins and 96 proteins were identified as differentially abundant proteins in UVB group and UVD groups, respectively. Proteins related to photosynthesis, amino acid biosynthesis, and tocopherol biosynthesis were significantly altered in UVB group, while proteins related to the biosynthesis of phenolic compounds were significantly altered in UVD group. In addition, the abundances of proteins involved in the ubiquitin-proteasome system (UPS) were significantly increased in both UVB and UVD groups, indicating that UPS combined with secondary mechanism participated in the resistance to UV-B radiation and dark incubation. The obtained results provide novel insight into the effects of high level UV-B radiation on M. alba leaves and on the strategies used for maximizing the chemical constituents and the medicinal value of the M. alba leaves.