The Genome-Wide Identification, Characterization and Expression Profiles of the High-Affinity Nitrate Transporter 2 Family Genes in Leymus chinensis, and Phenotypic Analysis of LcNRT2.21 Heterologous Overexpression in Rice

The tiller number of perennial grasses responds strongly to soil nitrogen availability, and critically governs aboveground biomass production. Plant NRT2 proteins are major components of the high-affinity nitrate transport system, and contribute to nitrate uptake and distribution, with gene-specific functions depending on tissue context, interacting partners, and nitrogen availability. However, few studies have explored the function of the NRT2 proteins in Leymus chinensis. In this study, 28 LcNRT2 genes were first identified in the L. chinensis genome. Phylogenetic analysis indicated that the 28 LcNRT2 genes were classified into four distinct clades. Gene structure analysis demonstrated that 82.1% of LcNRT2 genes were characterized by a lack of introns. While, 17.9% possessed only a single intron. Chromosomal localization indicated that 28 LcNRT2 genes were distributed on 8 of 14 chromosomes of L. chinensis. No LcNRT2 genes were identified on chromosomes 1Ns, 2Ns, 2Xm, 4Ns, 5Ns, and 5Xm. Six LcNRT2 genes were isolated from the nitrogen-induced transcriptome dataset of L. chinensis and exhibited significantly upregulated expression. LcNRT2.21 was significantly upregulated under nitrogen treatment, and was, therefore, studied in more detail. The heterologous overexpression of LcNRT2.21 in rice increased tiller number, decreased plant height, and altered the expression of tillering-related genes OsTB1, OsMOC1, OsYUCCA4 and OsAUX1. These results demonstrated that LcNRT2.21 may play a vital role in improving tiller numbers in plants.