Abstract
Magnesium (Mg(2+)) 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-Mg (2+) stress in tea plants remain largely unknown. In this study, photosynthetic parameters, metabolomics, and transcriptomics were utilized to explore the potential effects of low Mg(2+) on the growth and metabolism of C. sinensis. Low-Mg(2+) 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 Mg(2+) shortage in C. sinensis shoots and roots, respectively. Integrated transcriptome and metabolome analyses revealed the possible reasons for the decreased contents of chlorophyll and catechins and the increased theanine content in C. sinensis roots. Weighted gene co-expression network analysis indicated that the Mg(2+) transport system was essential in the regulation of Mg(2+) 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 chlorophyll in C. sinensis shoots. In addition, CsMGT5 might collaborate with ammonium transporters to keep the amino acid content steady, suggesting its potential application for tea quality improvement. All these findings demonstrate the key roles of CsMGTs for Mg(2+) homeostasis in C. sinensis, providing a theoretical basis for Mg(2+) efficient utilization in plants.