Measurement of metabolite variations and analysis of related gene expression in Chinese liquorice (Glycyrrhiza uralensis) plants under UV-B irradiation

Xiao Zhang,Li Peng,Jie Luo,Yingbai Shen,Yingying Chen,Xiaoli Ding,Yaxi Ji,Shouchuang Wang

doi:10.1038/s41598-018-24284-4

Abstract

Plants respond to UV-B irradiation (280–315 nm wavelength) via elaborate metabolic regulatory mechanisms that help them adapt to this stress. To investigate the metabolic response of the medicinal herb Chinese liquorice (Glycyrrhiza uralensis) to UV-B irradiation, we performed liquid chromatography tandem mass spectrometry (LC-MS/MS)-based metabolomic analysis, combined with analysis of differentially expressed genes in the leaves of plants exposed to UV-B irradiation at various time points. Fifty-four metabolites, primarily amino acids and flavonoids, exhibited changes in levels after the UV-B treatment. The amino acid metabolism was altered by UV-B irradiation: the Asp family pathway was activated and closely correlated to Glu. Some amino acids appeared to be converted into antioxidants such as γ-aminobutyric acid and glutathione. Hierarchical clustering analysis revealed that various flavonoids with characteristic groups were induced by UV-B. In particular, the levels of some ortho-dihydroxylated B-ring flavonoids, which might function as scavengers of reactive oxygen species, increased in response to UV-B treatment. In general, unigenes encoding key enzymes involved in amino acid metabolism and flavonoid biosynthesis were upregulated by UV-B irradiation. These findings lay the foundation for further analysis of the mechanism underlying the response of G. uralensis to UV-B irradiation.

Highlights

Plants inevitably encounter environmental stresses due to their sessile nature
Leaf samples were subjected to liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) and based on non-targeted metabolomics, principal component analysis (PCA) was performed to evaluate the variations in the levels of metabolites
These results indicated that UV-B did not cause metabolic changes after 12 and 24 h of irradiation, but it induced marked metabolic differences in leaves after more than 48 h irradiation, with the most prominent metabolic profile changes observed in seedlings treated with 96 h UV-B irradiation, compared to the controls

Summary

Introduction

Plants inevitably encounter environmental stresses due to their sessile nature. With the depletion of the stratospheric ozone layer, an increasing amount of UV-B radiation has been reaching the Earth’s surface and the surfaces of plants[1]. Plants produce elevated levels of several amino acids (i.e., Ala, Glu, Lys, and Phe) and some of their derivatives (i.e., γ-amino butyrate) under UV-B irradiation[4] This response occurs at the primary metabolic level after short-term UV-B treatment, which triggers elaborate changes in the production of functional secondary metabolites that can protect against UV-B damage[4,5]. G. uralensis is mainly found in arid, semi-arid, and desert areas of northwest China and is exposed to harsh conditions such as drought, cold, high-salinity soil, and UV-B radiation[28,29] These stresses may induce the activity of various metabolic pathways that contribute to the stress resistance of G. uralensis. We performed transcriptome analysis to explore the mechanism underlying the metabolic variation and regulation in G. uralensis leaves induced by UV-B irradiation, shedding light on the stress response in this important medicinal herb

Methods

Results

Conclusion