Cisgenic overexpression of cytosolic glutamine synthetase improves nitrogen utilization efficiency in barley and prevents grain protein decline under elevated CO₂

Abstract

Summary Cytosolic glutamine synthetase (GS1) plays a central role in nitrogen (N) metabolism. The importance of GS1 in N remobilization during reproductive growth has been reported in cereal species but attempts to improve N utilization efficiency (NUE) by overexpressing GS1 have yielded inconsistent results. Here, we demonstrate that transformation of barley ( Hordeum vulgare L.) plants using a cisgenic strategy to express an extra copy of native HvGS1‐1 lead to increased HvGS1.1 expression and GS1 enzyme activity. GS1 overexpressing lines exhibited higher grain yields and NUE than wild‐type plants when grown under three different N supplies and two levels of atmospheric CO 2 . In contrast with the wild‐type, the grain protein concentration in the GS1 overexpressing lines did not decline when plants were exposed to elevated (800–900 μL/L) atmospheric CO 2 . We conclude that an increase in GS1 activity obtained through cisgenic overexpression of HvGS1‐1 can improve grain yield and NUE in barley. The extra capacity for N assimilation obtained by GS1 overexpression may also provide a means to prevent declining grain protein levels under elevated atmospheric CO 2 .

Transcriptome analysis reveals Nitrogen deficiency induced alterations in leaf and root of three cultivars of potato (Solanum tuberosum L.)

“…There are various genes associated with N absorption and utilization, like nitrate transporters ( NRTs ), nitrate reductase ( NR ), glutamine synthetase ( GS ), glutamate dehydrogenase ( GDH ) and nitrite reductase ( NiR ) [ 12 ]. It has been reported that the GS overexpressing plant can increase the UTE and UPE in wheat and barley, which results in increasing crop yields [ 14 , 15 ]. Understanding the relationship of gene expression pattern and NUE is important for potato breeding.…”

Improving coordination of plant growth and nitrogen metabolism for sustainable agriculture

“…More importantly, up-regulations of some N metabolism genes in different crop species, for example, OsGS2 in rice (James et al 2018), TaGS2-2 in wheat (Hu et al 2018), HvGS1-1 in barley (Gao et al 2019a), and Gln1-3 and Gln1-4 in maize (Martin et al 2006), have been shown to increase N uptake and assimilation, and consequently enhance plant NUE and grain yields ( Fig. 1).…”

Biotechnological strategies for improved photosynthesis in a future of elevated atmospheric CO2

“…However, in a handful of cases it led to improved photosynthesis and biomass/grain yields, at least under high-light and low-nitrogen availability, and sometimes also in the presence of high nitrogen levels (Fuentes et al 2001;Oliveira et al 2002;Hu et al 2018;Kaur et al 2019). For example, the cisgenic expression of a barley cytosolic glutamine synthetase gene has been found to lead to higher grain yields and NUE in transgenic plants than wild type regardless of the nitrogen supply (Gao et al 2018). Intriguingly, these plants also exhibited similar benefits, and unlike wild-type plants were able to maintain grain quality in terms of protein levels, at e[CO 2 ] (800-900 ppm) (Tables 1, 5; Gao et al 2018), which indicates that this strategy deserves further study, in both ambient and e[CO 2 ].…”

“…For example, the cisgenic expression of a barley cytosolic glutamine synthetase gene has been found to lead to higher grain yields and NUE in transgenic plants than wild type regardless of the nitrogen supply (Gao et al 2018). Intriguingly, these plants also exhibited similar benefits, and unlike wild-type plants were able to maintain grain quality in terms of protein levels, at e[CO 2 ] (800-900 ppm) (Tables 1, 5; Gao et al 2018), which indicates that this strategy deserves further study, in both ambient and e[CO 2 ].…”