Metabolome profiling and transcriptome analysis unveiling the crucial role of magnesium transport system for magnesium homeostasis in tea plants

Magnesium (Mg2+) is a crucial nutrient for the growth and development of Camellia sinensis and is closely related to the quality of tea. However, the underlying mechanisms responding to low-Mg2+ stress in tea plants remain largely unknown. In this study, the photosynthetic parameters, metabolomics, and transcriptomics were utilized to explore the potential effects of low-Mg2+ on the growth and metabolism of C. sinensis. Low-Mg2+ treatment increased the ratio of shoot dry weight to root dry weight but decreased the photosynthesis of C. sinensis. Forty and thirty metabolites were impacted by Mg2+ shortage in C. sinensis shoots and roots, respectively. Integrated transcriptome and metabolome analyses revealed the possible reasons for the decreased contents of chlorophyll (Chl) and catechins and the increased theanine content in C. sinensis roots. Weighted gene co-expression network analysis indicated that Mg2+ transport system was essential in regulation of Mg2+ homeostasis in C. sinensis, in which CsMGT5 was identified to be the key regulator according to CsMGT5-overexpressing and complementary assays in Arabidopsis thaliana. Moreover, silencing of CsMGT5 in vivo reduced the content of Chl in C. sinensis shoots. In addition, CsMGT5 might collaborate with ammonium transporters to keep the steady of amino acids contents, suggesting its potential application for tea quality improvement. All these findings demonstrate the key roles of CsMGTs for Mg2+ homeostasis in C. sinensis, providing theoretical basis for Mg2+ efficient utilization in plants.