Expression of Rice (Oryza sativa L.) Genes Involved in High-Affinity Nitrate Transport during the Period of Nitrate Induction

Abstract

When breeding crops that utilize nitrogen efficiently, it is important to reveal the regulation of nitrate uptake at the molecular level. We focused on the expression of two nitrate uptake-related genes, NRT2 and NAR2, and nitrate uptake during the nitrate induction. Four rice NRT2s (OsNRT2.1~2.4) and two NAR2s (OsNAR2.1~2.2) were identified in the rice genome database. We analyzed the expression of the genes in the roots and shoots after supply of nitrate with or without ammonium pretreatment by the RT-PCR method. The apparent nitrate uptake was also measured. Differential expression of OsNRT2.1 and OsNRT2.2, which have the same ORF with different 5′-and 3′-UTR, was observed in the seedlings pretreated with ammonium. The apparent nitrate uptake synchronously increased after supply of nitrate with the expression pattern of OsNRT2.1 in roots either with or without ammonium pretreatment. The expression of OsNAR2.1, which is thought to be an activator gene for the function of NRT2, was also coordinated with that of OsNRT2.1. On the other hand, OsNRT2.2 was already expressed after ammonium pretreatment, suggesting that OsNRT2.2 would be transcribed to take up nitrate in flooded soils. The present results indicate that OsNRT2.1, OsNRT2.2 and OsNAR2.1 are candidate genes when breeding for efficient use of nitrate in rice.

Nitrate transporters: an overview in legumes

“…Using similar approaches, Pellizzaro et al (2015) revealed, for M. truncatula, a small NRT2 gene family composed of three MtNRT2 genes (named MtNRT2.1, MtNRT2.2 and MtNRT2.3), indicating a similar NRT2 family size in legume or non-legume species. Indeed, seven AtNRT2 genes were identified in A. thaliana (Orsel et al 2002a, b;Okamoto et al 2003) and four in rice (Araki and Hasegawa 2006;Cai et al 2008;Feng et al 2011). In these non-legume species, all characterized NRT2s have been reported to be strictly high-affinity nitrate transporters (Feng et al 2011;Krapp et al 2014).…”

Two-component high-affinity nitrate transport system in barley: Membrane localization, protein expression in roots and a direct protein-protein interaction

“…Many studies of the molecular basis of nitrate uptake reveal the existence of two gene families, namely the NRT1 and NRT2 families, which potentially encode for LATS and HATS respectively. NRT2 genes are identified in a variety of organisms including fungi, certain yeasts, green algae, and higher plants ( Unkles et al 1991;Quesada et al 1994;Trueman et al 1996;Pérez et al 1997;Quesada et al 1997;Amarasinghe et al 1998;Zhuo et al, 1999;Araki and Hasegawa 2006;Tsujimoto et al 2007). In most species, NRT2 genes are members of a multigene family: for example, seven Arabidopsis genes (AtNRT2.1-AtNRT2.7) and four rice genes (OsNRT2.1-OsNRT2.4) have been found in their genomes (Orsel et al 2002; Araki and Hasegawa 2007), and at least four NRT2 genes (HvNRT2.1-HvNRT2.4) exist in barley (Vidmar 2000a).…”

Production and characterization of transgenic rice plants carrying a high-affinity nitrate transporter gene (OsNRT2.1)

“…In the wild-type plants, transcripts of OsNRT2.1, OsNRT2.2 and OsNRT2.4 in roots were detected starting 30 min after the beginning of nitrate treatment, suggesting that a short induction period exists in rice as reported by Araki and Hasegawa (2006). Transcripts of OsNRT2.3 were constitutively expressed.…”

“…It is of practical importance to improve the efficiency of nitrate uptake in paddy rice. As the nitrate concentration in the rhizosphere of paddy fields is estimated to be 1-10 μM (Kirk and Kronzucker 2005), in rice, NRT2 appears to play a major role in nitrate uptake (Araki and Hasegawa 2006). As in higher plants such as Arabidopsis thaliana (Orsel et al 2002) and barley (Vidmar et al 2000), rice has NRT2 family genes that are differentially regulated.…”

“…As in higher plants such as Arabidopsis thaliana (Orsel et al 2002) and barley (Vidmar et al 2000), rice has NRT2 family genes that are differentially regulated. In rice, four NRT2s have been identified and OsNRT2.1 and OsNRT2.2 are thought to play a major role in nitrate assimilation (Araki and Hasegawa 2006).…”