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.