Identification of Regulatory Networks and Hub Genes Controlling Nitrogen Uptake in Tea Plants [Camellia sinensis (L.) O. Kuntze].

Nitrogen (N) uptake, as the first step of N metabolism, is a key limiting factor for plant growth. To understand the gene expression networks that control N absorption and metabolism in tea plants, we analyzed transcriptomes in the young roots of two groups of tea plants with significantly different growth rates under different N treatments (0, 0.2, and 2 mM). Using pairwise comparisons and weighted gene co-expression network analyses (WGCNA), we successfully constructed 16 co-expression modules. Among them, a specific module (turquoise) that substantially responded to the low N treatment was identified. Based on KEGG analysis, the relative genes that enriched in the "N metabolism" pathways were used to construct gene co-expression networks of N metabolism. Finally, a high-affinity ammonium (NH4+) transporter designated CsAMT1.2 was identified as a hub gene in the N metabolism network in tea plant roots and the gene expression could be highly induced by N resupply. The gene functional analysis revealed that CsAMT1.2 could make functional complementation of MEP1, MEP2, and MEP3 genes in 31019b yeast cells and improve NH4+ uptake rate in 31019b at low NH4+ level. Thus, CsAMT1.2 was a key gene controlling N uptake in tea plants and might play a vital role in promoting NH4+ uptake from the environment in tea roots. This study provided a useful foundation for improving the NUE in tea plantations.