Background: Tea plant (Camellia sinensis) is one of the most popular non-alcoholic beverages worldwide. In tea, lateral roots (LRs) are the main organ responsible for the absorption of moisture and mineral nutrients from the soil. Lateral roots formation and development are regulated by the nitrogen and auxin signaling pathways. In order to understand the role of auxin and nitrogen signaling in LRs formation and development, transcriptome analysis was employed to investigate the differentially expressed genes involved in lateral roots of tea plants treated with indole-3-butyric acid (IBA), N-1-naphthylphthalamic acid (NPA), low and high concentrations of nitrogen. Results: A total of 296 common differentially expressed genes were identified and annotated to four signaling pathways, including nitrogen metabolism, plant hormone signal transduction, glutathione metabolism and transcription factors. RNA-sequencing results revealed that majority of differentially expressed genes play important roles in nitrogen metabolism and hormonal signal transduction. Low nitrogen condition induced the biosynthesis of auxin and accumulation of transcripts, thereby, regulating lateral roots formation. Furthermore, metabolism of cytokinin and ethylene biosynthesis were also involved in lateral roots development. Transcription factors like MYB genes also contributed to lateral roots formation of tea plants through secondary cell wall biosynthesis. Reversed phase ultra performance liquid chromatography (RP-UPLC) results showed that the auxin concentration increased with the decreased nitrogen level in lateral roots. Thus, tea plant lateral roots formation could be induced by low nitrogen concentration via auxin biosynthesis and accumulation. Conclusion: This study provided insights into the mechanisms associated with nitrogen and auxin signaling pathways in LRs formation and provides information on the efficient utilization of nitrogen in tea plant at the genetic level.

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Background Tea plant (Camellia sinensis) is one of the most popular non-alcoholic beverage worldwide. Lateral roots (LRs) of tea plant are the main organ used for tea plant to absorb soil moisture and nutrients. Lateral roots formation and development are tightly regulated by the nitrogen and auxin signaling pathway. In order to understand the function of auxin and nitrogen signaling in LRs formation and development, transcriptome analysis was applied to investigate the differentially expressed genes involved in lateral roots of tea plants treated with indole-3-butyric acid (IBA), N-1-naphthylphthalamic acid (NPA), low and high nitrogen concentration. Results A total of 296 common differentially expressed genes were mainly identified and annotated to four signaling pathways, such as nitrogen metabolism, plant hormone signal transduction, Glutathione metabolism and transcription factors. RNA-sequencing results revealed that majority of differentially expressed genes play important roles in nitrogen metabolism and hormonal signal transduction. Low nitrogen condition induced the biosynthesis of auxin and accumulation of transcripts, thereby regulating lateral roots formation. Furthermore, metabolism of cytokinin and ethylene biosynthesis were also involved in lateral roots development. Transcription factors like MYB genes also contributed to the lateral roots formation of tea plants through secondary cell wall biosynthesis. Reversed phase ultra performance liquid chromatography (RP-UPLC) results showed that the auxin concentration in lateral roots was increased, while the nitrogen level decreased. Thus, tea plant lateral roots formation could be induced by low nitrogen concentration via auxin biosynthesis and accumulation. Conclusion This study provides new insights into the mechanisms associated with nitrogen and auxin signaling pathways to regulate LRs formation and arises new clues for the efficient utilization of nitrogen in tea plant at the genetic level.

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Pruning is an important plant management practice in tea cultivation. However, the mechanism underlying the dynamics of nutrient uptake by roots of pruned tea is unknown. This study investigated the metabolic alterations in lateral roots of pruned tea to unveil the mechanism of nutrient uptake. Elemental analysis revealed that pruning significantly increases the uptake of nutrients by lateral roots. Metabolic profiling showed significant metabolic variations in lateral roots of pruned tea. Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis revealed that flavonoid biosynthesis, phenylpropanoid biosynthesis, and amino acid metabolism were differentially regulated in lateral roots. Caffeine metabolism was significantly hindered, while ethylene signaling was significantly induced in lateral roots of pruned plants. In addition, intermediates in the tricarboxylic acid (TCA) cycle were upregulated, indicating high rates of the TCA cycle. Therefore, pathways related to phenylpropanoid biosynthesis, TCA cycle, ethylene biosynthesis, and metabolism of amino acids contribute to higher nutrient uptake by lateral roots of the tea plant.

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