Impacts of environmental conditions, and allelic variation of cytosolic glutamine synthetase on maize hybrid kernel production

Abstract

Cytosolic glutamine synthetase (GS1) is the enzyme mainly responsible of ammonium assimilation and reassimilation in maize leaves. The agronomic potential of GS1 in maize kernel production was investigated by examining the impact of an overexpression of the enzyme in the leaf cells. Transgenic hybrids exhibiting a three-fold increase in leaf GS activity were produced and characterized using plants grown in the field. Several independent hybrids overexpressing Gln1-3, a gene encoding cytosolic (GS1), in the leaf and bundle sheath mesophyll cells were grown over five years in different locations. On average, a 3.8% increase in kernel yield was obtained in the transgenic hybrids compared to controls. However, we observed that such an increase was simultaneously dependent upon both the environmental conditions and the transgenic event for a given field trial. Although variable from one environment to another, significant associations were also found between two GS1 genes (Gln1-3 and Gln1-4) polymorphic regions and kernel yield in different locations. We propose that the GS1 enzyme is a potential lead for producing high yielding maize hybrids using either genetic engineering or marker-assisted selection. However, for these hybrids, yield increases will be largely dependent upon the environmental conditions used to grow the plants.

A revised view on the evolution of glutamine synthetase isoenzymes in plants

“…Cytosolic GS isoforms are mostly involved in primary N assimilation in roots and N remobilization and translocation in shoots (Thomsen et al., 2014). As such, it has been shown that they play a key role during plant growth and development, notably for biomass and storage organ production (Xu et al., 2012; Krapp, 2015; Havé et al., 2017; Amiour et al., 2021). In conifers, as a result of the absence of GS2, studies have focused on GS1a and GS1b, which are each encoded by a single gene.…”

The Role of Glutamine Synthetase (GS) and Glutamate Synthase (GOGAT) in the Improvement of Nitrogen Use Efficiency in Cereals

“…Moreover, these transgenic plants had an increased chlorophyll content and photosynthesis efficiency, suggesting that the improved transfer of photosynthate from vegetative organs supports photosynthesis at the reproductive stage and slows down leaf senescence [142]. The overexpression of Gln1-3 in the leaf and bundle sheath mesophyll cells of maize permitted an increase in kernel yield, which was mostly dependent upon the environmental conditions [143].…”

Genetic Engineering and Genome Editing for Improving Nitrogen Use Efficiency in Plants

“…In Urriola et al [ 97 ], the biomass and yield of sorghum plants overexpressing a cytosolic GS ( Gln1 ) gene under control of a pUbi differed significantly between greenhouse experiments in winter and spring. The environmental effect on NUE was later demonstrated in extensive field trials (over 5 years in ten different locations) on maize overexpressing two copies of a Gln1-3 (GS1) gene in the mesophyll cells (CsVMV promoter) and in the bundle sheet (RbcS promoter) [ 103 ]. The yield of transgenic plants increased by an average of 3.8%, but this increase depended on both environmental conditions and the transgenic line used.…”