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

Abstract

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.

Root-specific secondary metabolism at the single-cell level: a case study of theanine metabolism and regulation in the roots of tea plants (Camellia sinensis)

“…In tea plant roots, both theanine biosynthesis and root development are regulated by N level and its form (Yang et al, 2020). Moreover, theanine is probably involved in N-regulated lateral root development (Chen et al, 2022). This implicates the presence of TFs that can co-regulate theanine biosynthesis and development in the tea root.…”

“…Besides, CsLBD37 is expressed in pericycle cells and also inhibits lateral root development. It is reported that apoplastic theanine can negatively regulate lateral root development, under high nitrogen levels (Chen et al, 2022). Therefore, CsLBD37 may also be involved in theanine-regulated lateral root development.…”

“…Recently, some TFs regulating CsTSI or CsAlaDC were identified and characterized and indicted that theanine regulates lateral root development (Chen et al, 2022;Guo et al, 2022;Zhang et al, 2021c); however, the molecular link between these processes was not elucidated.…”

“…Recently, some TFs regulating CsTSI or CsAlaDC were identified and characterized and indicted that theanine regulates lateral root development (Chen et al, 2022; Guo et al, 2022; Zhang et al, 2021c); however, the molecular link between these processes was not elucidated. Previous studies have shown that several LBD family members regulate proanthocyanidin (PA) metabolism and are involved in root development in response to N in Arabidopsis thaliana (Rubin et al, 2009).…”

CsMYB73 negatively regulates theanine accumulation mediated by CsGGT2 and CsGGT4 in tea shoots (Camellia sinensis)

“…Previous studies have indicated that the accumulation of theanine is subject to dynamic regulation influenced by various factors, such as the growth of tea plants and environmental factors, including development, season, temperature, light, and other abiotic and biotic stresses [ 33–35 ]. Tea plants accumulate theanine dynamically as a result of biosynthesis, degradation, and transport processes, all of which are coregulated by genetics, nitrogen status, and the environment [ 1 , 6 , 36 ].…”