Genome-Wide Identification of AMT2-Type Ammonium Transporters Reveal That CsAMT2.2 and CsAMT2.3 Potentially Regulate NH Absorption among Three Different Cultivars of .

Ammonium (NH), as a major inorganic source of nitrogen (N) for tea plant growth, is transported and distributed across membranes by the proteins of ammonium transporters (AMTs). However, the AMT2-type AMTs from tea plants remain poorly understood. In this study, five subfamily genes were identified in tea plant genomes, and their full-length coding sequences (CDS) were isolated from roots. Then, a NH uptake kinetic comparison of Fudingdabaicha (FD), Huangdan (HD), and Maoxie (MX) showed that FD was a high N efficiency (HNE) cultivar that had a wide range of adaptability to NH, HD was a high N efficiency under high N conditions (HNEH) cultivar, in which it was easy to obtain higher yield in a high N environment, and MX was a high N efficiency under low N conditions (HNEL) cultivar, which had a higher affinity for NH than the other two. Tissue-specific expression analysis suggested that and were highly expressed in the roots, indicating that these two members may be unique in the subfamily. This is further supported by our findings from the temporal expression profiles in the roots among these three different N adaptation cultivars. Expression levels of and in FD and HD were upregulated by a short time (2 h) under high NH treatment, while under low NH treatment, and were highly expressed at 0 h and 2 h in the HNEL-type cultivar-MX. Furthermore, the functional analysis illustrated that and could make a functional complementation of NH-defective mutant yeast cells at low NH levels, and the transport efficiency of was higher than that of . Thus, we concluded that and might play roles in controlling the NH uptake from the soil to the roots. These results will further the understanding of the NH signal networks of AMT2-type proteins in tea plants.