Transcriptome Analysis Revealed the Mechanism of Nitrate Absorption in Tea Plants

Nitrate (NO₃^-) serves as a critical nitrogen source and signaling molecule essential for its growth and quality formation. Although substantial genetic variation in nitrogen use efficiency (NUE) has been documented among tea cultivars, a systematic characterization of nitrate (NO₃^-) absorption kinetics and the associated genome-wide transcriptional regulatory networks across varying nitrate concentrations remains lacking. This study employed ¹⁵N isotope labeling and transcriptome sequencing to systematically analyze the absorption characteristics and molecular response mechanisms of the cultivars 'Longjing 43' and 'Zhongming 6 hao' under varying NO₃^- concentrations. Results revealed significant differentiation in absorption strategies: 'Zhongming 6 hao' exhibited a significantly higher absorption rate at low concentrations, whereas 'Longjing 43' demonstrated enhanced performance at high concentrations. Transcriptome analysis indicated that both cultivars shared coordinated regulation of 'photosynthesis' and 'nitrogen metabolism' pathways. Furthermore, 14 nitrogen metabolism genes and 64 differentially expressed transcription factors (including MYB, NAC, and LBD families) were identified. Specifically, the CsNiR gene (encoding nitrite reductase) was functionally validated; silencing of CsNiR significantly reduced nitrite reductase activity, confirming its positive regulatory role. This study provided a theoretical framework and key candidate genes for breeding nitrogen-use-efficient varieties, which is essential for sustainable tea production.