A glutamine synthetase-Dof transcription factor module regulates nitrogen remobilization from source to sink tissues in tea plants.

Nitrogen (N) remobilization from mature leaves to new shoots (NSs) is closely related to the quality of green tea in the spring season, which subsequently determines its economic value. However, the underlying N remobilization mechanism remains poorly understood. Here, we demonstrate that >80% of the recovered 15N was partitioned in the first mature leaves that supply NSs. N-remobilization efficiency (NRE) from mature leaves to NSs varied significantly among tea cultivars. N-fertilization level and NRE showed a significantly positive correlation. Based on weighted gene co-expression network analysis, glutamate metabolism-related genes, including glutamine synthetase genes, CsGSs, were dissected from the interaction network of hub genes regulating N remobilization. Gene expression patterns and the localization of CsGS1.1 in the cytosol and vascular tissue suggest its potential role in N remobilization. Consistent with these findings, source-to-sink N remobilization at the reproductive stage was enhanced in transgenic CsGS1.1-overexpressing plants. Furthermore, we demonstrated that the Dof transcription factor CsDof16 directly binds to the -526 to -426 region of the CsGS1.1 promoter, thereby activating its transcription and regulating N remobilization. Taken together, our findings suggest that the CsDof16-CsGS1.1 module regulates the remobilization of N in the form of glutamate/glutamine from mature leaves to NSs, constituting an important control point in the regulation of source-to-sink N partitioning in tea plants. Our findings can be employed to reduce fertilizer application and promote the development of sustainable tea production.