Theanine, a tea plant specific non-proteinogenic amino acid, is involved in the regulation of lateral root development in response to nitrogen status


 Glutamine synthetase type I (GSI)-like proteins are proposed to mediate nitrogen signaling and developmental fate by synthesizing yet unidentified metabolite. Theanine, the most abundant non-proteinogenic amino acid in tea plants, is the first identified metabolite synthesized by GSI-like protein (CsTSI) in living system. However, the roles of theanine in nitrogen signaling and development are rarely understood. In the study, we found nitrogen deficiency significantly reduced theanine accumulation and increased lateral root development in tea plant seedlings. Exogenous theanine feeding significantly repressed lateral roots development of tea plant seedlings and model plant Arabidopsis. The transcriptomic analysis revealed that the differentially expressed genes in the roots under theanine feeding were enriched in apoplastic pathway and H2O2 metabolism. Consistently, theanine feeding reduced H2O2 levels in the roots. Importantly, when co-treated with H2O2, theanine abolished the promoting effect of H2O2 on lateral root development, in both tea plant and Arabidopsis seedlings. The results of histochemistric assays confirmed that theanine inhibited reactive oxygen species (ROS) accumulation in the roots. The further transcriptomic analyses suggested the expression of genes encoding enzymes of H2O2 generation and scavenging was down- and up-regulated by theanine, respectively. Moreover, the expression of genes in auxin metabolism and signaling, cell division and cell expansion was also regulated by theanine. Collectively, these results suggested CsTSI-synthesized theanine is likely involved in the regulation of lateral root development, via modulating H2O2 accumulation, in response to nitrogen levels in tea plants. This study also implied that the module consisting of GSI-like protein and theanine-like metabolite is probably conserved in regulating development in response to nitrogen status in plant species.