Nitrogen (N) is a macroelement with an indispensable role in the growth and development of plants, and tea plant (Camellia sinensis) is an evergreen perennial woody species with young shoots for harvest. During senescence or upon N stress, autophagy has been shown to be induced in leaves, involving a variety of autophagy-related genes (ATGs), which have not been characterized in tea plant yet. In this study, a genome-wide survey in tea plant genome identified a total of 80 Camellia Sinensis autophagy-related genes, CsATGs. The expression of CsATG8s in the tea plant showed an obvious increase from S1 (stage 1) to S4 (stage 4), especially for CsATG8e. The expression levels of AtATGs (Arabidopsis thaliana) and genes involved in N transport and assimilation were greatly improved in CsATG8e-overexpressed Arabidopsis. Compared with wild type, the overexpression plants showed earlier bolting, an increase in amino N content, as well as a decrease in biomass and the levels of N, phosphorus and potassium. However, the N level was found significantly higher in APER (aerial part excluding rosette) in the overexpression plants relative to wild type. All these results demonstrated a convincing function of CsATG8e in N remobilization and plant development, indicating CsATG8e as a potential gene for modifying plant nutrient utilization.
For tea plants, nitrogen (N) is a foundational element and large quantities of N are required during periods of roundly vigorous growth. However, the fluctuation of N in the tea garden could not always meet the dynamic demand of the tea plants. Autophagy, an intracellular degradation process for materials recycling in eukaryotes, plays an important role in nutrient remobilization upon stressful conditions and leaf senescence. Studies have proven that numerous autophagy-related genes (ATGs) are involved in N utilization efficiency in Arabidopsis thaliana and other species. Here, we identified an ATG gene, CsATG101, and characterized the potential functions in response to N in A. thaliana. The expression patterns of CsATG101 in four categories of aging gradient leaves among 24 tea cultivars indicated that autophagy mainly occurred in mature leaves at a relatively high level. Further, the in planta heterologous expression of CsATG101 in A. thaliana was employed to investigate the response of CsATG101 to low N stress. The results illustrated a delayed transition from vegetative to reproductive growth under normal N conditions, while premature senescence under N deficient conditions in transgenic plants vs. the wild type. The expression profiles of 12 AtATGs confirmed the autophagy process, especially in mature leaves of transgenic plants. Also, the relatively high expression levels for AtAAP1, AtLHT1, AtGLN1;1, and AtNIA1 in mature leaves illustrated that the mature leaves act as the source leaves in transgenic plants. Altogether, the findings demonstrated that CsATG101 is a candidate gene for improving annual fresh tea leaves yield under both deficient and sufficient N conditions via the autophagy process.
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