Overexpression of the High-Affinity Nitrate Transporter OsNRT2.3b Driven by Different Promoters in Barley Improves Yield and Nutrient Uptake Balance

Abstract

Improving nitrogen use efficiency (NUE) is very important for crops throughout the world. Rice mainly utilizes ammonium as an N source, but it also has four NRT2 genes involved in nitrate transport. The OsNRT2.3b transporter is important for maintaining cellular pH under mixed N supplies. Overexpression of this transporter driven by a ubiquitin promoter in rice greatly improved yield and NUE. This strategy for improving the NUE of crops may also be important for other cereals such as wheat and barley, which also face the challenges of nutrient uptake balance. To test this idea, we constructed transgenic barley lines overexpressing OsNRT2.3b. These transgenic barley lines overexpressing the rice transporter exhibited improved growth, yield, and NUE. We demonstrated that NRT2 family members and the partner protein HvNAR2.3 were also up-regulated by nitrate treatment (0.2 mM) in the transgenic lines. This suggests that the expression of OsNRT2.3b and other HvNRT2 family members were all up-regulated in the transgenic barley to increase the efficiency of N uptake and usage. We also compared the ubiquitin (Ubi) and a phloem-specific (RSs1) promoter-driven expression of OsNRT2.3b. The Ubi promoter failed to improve nutrient uptake balance, whereas the RSs1 promoter succeed in increasing the N, P, and Fe uptake balance. The nutrient uptake enhancement did not include Mn and Mg. Surprisingly, we found that the choice of promoter influenced the barley phenotype, not only increasing NUE and grain yield, but also improving nutrient uptake balance.

Genome-Wide Association Study and Identification of Candidate Genes for Nitrogen Use Efficiency in Barley (Hordeum vulgare L.)

“…Atnrt2.7 mutants had an average of 50% nitrate reduction in seeds compared to the wild type. High affinity nitrate transporter OsNRT2.3b has been successfully overexpressed in barley transgenic lines to improve yield and nutrient uptake balance by Luo et al (2020) using hydroponics with a nearly similar concentration of N to our study. Another NRT2 gene HvNRT2.1 was found to improve yield in Arabidopsis under low-N (Guo et al, 2020).…”

The functional characterization of LjNRT2.4 indicates a novel, positive role of nitrate for an efficient nodule N2‐fixation activity

“…The nitrate transport capacity has been reported for the whole family of A. thaliana and O. sativa NRT2 proteins (Wei et al ., 2018; Wang et al ., 2018), as well as for the characterized NRT2 members of Brassica napus, Lycopersicon esculentum, Chrysanthemum morifolium, Cucumis sativa, Cassava and Brachypodium distachyon (Leblanc et al ., 2013; Fu et al ., 2015; Gu et al ., 2016; Li et al ., 2018; Wang et al ., 2019; L. Zou et al ., 2019). Furthermore, specific links between altered NRT2 gene expression obtained in mutant or overexpressing genetic backgrounds and nitrate‐related plant phenotypes havebeen reported in many plants, including Triticum aestivum and Zea mays (Fu et al ., 2015; He et al ., 2015; Taulemesse et al ., 2015; Gu et al ., 2016; Ibrahim et al ., 2017; Wei et al ., 2018; Li et al ., 2018; Wang et al ., 2018; Naz et al ., 2019; L. Zou et al ., 2019; Luo et al ., 2020). The reduced NO production and content detected in the Ljnrt2.4 nodules are consistent with a deficient support of the nitrate substrate (Fig.…”

Phylogenomic and Microsynteny Analysis Provides Evidence of Genome Arrangements of High-Affinity Nitrate Transporter Gene Families of Plants

“…In Com5_NRT2, orthologues of AtNRT2.5 were found in the monocots O. sativa (OsNRT2.3) [ 25 , 95 ], H. vulgare (HvNRT2.1) [ 35 ], and Z. may (ZmNRT2.5) [ 34 ], differing in genomic context with from their A. thaliana orthologue, which was identified in Com3NRT2 ( Figure 5 ).…”