Transcriptomic and metabolomic profiling of Camellia oleifera seedling roots treated with different nitrogen forms

Nitrogen (N)is an essential nutrient for plant growth, but its availability is limited in the soil of subtropical ecosystems. Identifying the genes responsible for N utilization efficiency (NUE)in Camellia oleifera is important because of the excessive cost of N fertilization. To investigate this, we performed RNA-sequencing of C. oleifera roots to reveal the genome-wide gene expression in response to three synthetic forms of N, namely ammonium (NH?+?4), nitrate (NO- 3), and ammonium nitrate (NH4NO3), provided to three independent groups of plants. The expression of several ammonium and nitrate transporters increased slightly in the NO- 3-treated group and significant changes were observed in the NH?+?4- and NH4NO3-treated groups. The opposite expressions of some key N transport and assimilation genes under the different N treatments suggested that C. oleifera might have different N utilization pathways for the different N forma. Additionally, the genes involved in N transport and assimilation account for the different N uptake and for different concentrations of glutamate and glutamine in plants and the metabolomic data showed that the accumulation of both amino-acids was promoted by the NH?+?4 and NH4NO3 treatments but not by the NO- 3 treatment. These findings will help improve the NUE of C. oleifera and guide its agricultural production in the future.