Tea plant (Camellia sinensis) is a well-known Al-accumulating plant, showing a high level of aluminum (Al) tolerance. However, the molecular mechanisms of Al tolerance and accumulation are poorly understood. We carried out transcriptome analysis of tea plant leaves in response to three different Al levels (0, 1, 4 mM, for 7 days). In total, 794, 829 and 585 differentially expressed genes (DEGs) were obtained in 4 mM Al vs. 1 mM Al, 0 Al vs. 1 mM Al, and 4 mM Al vs. 0 Al comparisons, respectively. Analysis of genes related to polysaccharide and cell wall metabolism, detoxification of reactive oxygen species (ROS), cellular transport, and signal transduction were involved in the Al stress response. Furthermore, the transcription factors such as zinc finger, myeloblastosis (MYB), and WRKY played a critical role in transcriptional regulation of genes associated with Al resistance in tea plant. In addition, the genes involved in phenolics biosynthesis and decomposition were overwhelmingly upregulated in the leaves treated with either 0 Al and 4 mM Al stress, indicating they may play an important role in Al tolerance. These results will further help us to understand mechanisms of Al stress and tolerance in tea plants regulated at the transcriptional level.
The application of organic fertilizer has been one of the most important agricultural practices to increase tea plant productivity. However, a single organic fertilizer alone could not match the nutrient requirements of tea plant. According to the nutrient demand of tea plant, tea-specific fertilizer with an appropriate nutrient ratio in combination with organic fertilizer would be an appropriate way. A four-year field experiment was conducted to characterize the sensory quality of green tea subjected to four different fertilization treatments, i.e., tea-specific fertilizer (N-P2O5-K2O: 18-8-12) + urea + colza cake, tea-specific fertilizer + urea + livestock waste compost, and tea-specific fertilizer + urea, combined tea-specific fertilizer (referred to as M1, M2, and M3, respectively); nonfertilizing (CK) served as control. The fertilizer formulated specifically for tea could enhance the taste qualities of green tea, such as water extract, caffeine, tea polyphenol, EGCG, and ECG. However, the effect of this fertilizer on enhancing the aroma level of green tea was weaker than that of the application of tea-specific fertilizer combined with organic fertilizer, whereby this combined fertilization significantly improved the concentration of green tea aroma compounds, such as D-limonene, cis-jasmone, nonanal, linalool, cis-3-hexenyl hexanoate, and cis-3-hexenyl benzoate. This study provides a theoretical basis for judicious fertilization by combining tea-specific fertilizer and organic fertilizer in tea orchards.
Background The major aluminum (Al) detoxication mechanism of tea plant (Camellia sinensis), as an Al hyperaccumulator plant, is the fixation of almost 70% of Al in the cell walls. Pectin is the primary constituent of cell walls, a degree of methylation of pectin polysaccharides regulated by the pectin methylesterase (PME) genes can greatly affect the Al binding capacity. The knowledge on PME gene family in tea plant is still poor. Results We identified 66 (CsPME1-CsPME66) PME genes from C. sinensis genome. We studied their protein characterization, conserved motifs, gene structure, systematic evolution and gene expression under Al treatments, to establish a basis for in-depth research on the function of PMEs in tea plant. Gene structures analysis revealed that the majority of PME genes had 2–4 exons. Phylogenetic results pointed out that the PME genes from the same species displayed comparatively high sequence consistency and genetic similarity. Selective pressure investigation suggested that the Ka/Ks value for homologous genes of PME family was less than one. The expression of CsPMEs under three Al concentration treatments was tissue specific, eight PME genes in leaves and 15 in roots displayed a trend similar to of the Al contents and PME activities under Al concentration treatments, indicating that the degree of pectin de-esterification regulated by PME was crucial for Al tolerance of tea plant. Conclusions Sixty-six CsPME genes were identified for the first time in tea plant. The genome-wide identification, classification, evolutionary and transcription analyses of the PME gene family provided a new direction for further research on the function of PME gene in Al tolerance of tea plant.
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