- Consequently, Tabuchi et al. re-named the previous two genes as OsGS1;1 for OsGS1 and OsGS1;2 for OsGSr.
- Although a small gene family for both GS and GOGAT is present in rice, ammonium-dependent and cell type-specific expression suggest that cytosolic GS1;2 and plastidic NADH-GOGAT1 are responsible for the primary assimilation of ammonium ions in the roots.
- GS1;2 and NADH-GOGAT1 could be key players in the assimilation of NH4+ taken up by rice roots. OsGS1;2 could provide a certain level of glutamine for growth of the mutants.
- A rice GS1;2, and an Escherichia coli glnA displayed an enhanced metabolic level quantified by increases in leaf total GS activities and soluble protein concentrations and higher total amino acids and total nitrogen contents in whole plants.
- Expression of OsGS1;2 in leaf blades and sheath was identical between the mutants and wild-type plants. As normal spikelets were rarely obtained from the mutants.
- The OsGS1;2 transcript was slightly abundant in the roots of the knockout mutants than those in wild-type seedlings.
- Significant increases in the leaf total GS activities of the GS-overexpressed plants under both normal nitrogen and low-nitrogen conditions were observed (18% for GS1;1-, 19% for GS1;2- and 25% for glnA-overexpressed plants under normal nitrogen condition; 36% for GS1;1-, 44% for GS1;2-, and 46% for glnA overexpressed plants under low-nitrogen condition.
- Both the plant height and fresh weight of GS1;2- and glnA-overexpressed plants under the NaCl concentration treatments were significantly lower than the negative control and wild-type plants.
- OsGS1;2 transcripts were also detected in all organs, with higher expression in the root following the supply of NH4+ at the seedling stage, while OsGS1;3 was specifically expressed in the spikelet. The OsGS1;1 and OsGS1;2 transcripts showed reciprocal responses to NH4+ supply in the surface cell layers of roots.
- OsAMT1;2, OsGS1;2, and OsNADH-GOGAT1 are rapidly and sequentially expressed in the two cell layers of the root surface, epidermal and exodermal cells, following the supply of NH4+ ions.
- Expression of OsAMT1;1, OsAMT1;2, OsGS1;1, OsGS1;2, and OsNADH-GOGAT1 was up- or down-regulated by exogenous NH4+ ions, respectively. OsGS1;2 was expressed mainly in roots. GS1;2 and GS1;3 were not able to compensate for GS1;1 function. GS1;2-overexpressed plants exhibited resistance to Basta selection and higher sensitivity to salt, drought, and cold stress conditions.
- GS1;2- and glnA-overexpressed plants but not GS1;1-overexpressed plants are sensitive to high salt conditions. GS1;2-overexpressed plants were highly sensitive to drought conditions compared to the wild-type plants.
Two homologous but distinct mRNA sequences of rice cytosolic isoenzymes of GS (named GS1;1 and GS1;2, 83% nucleotide homology and 85% amino acid homology within the coding region) were found in NCBI GenBank database, and two EST clones encoded GS1;1 and GS1;2.
- The different results for free NO3- in the GS overexpressed plants may indicate distinct roles of GS1;1 and GS1;2 in nitrogen assimilation. GS1;2 is highly expressed in roots and mainly functions in primary NH4+ assimilation, while GS1;1 is highly expressed in shoot phloem tissues and therefore functions in translocating nitrogenous compounds to the developing sink tissues.
- Higher GS1;2 mRNA transcripts in GS1;2-overexpressed plants can accelerate the reduction from NO3- to NH4+ to decrease the nitrate level in cells, and higher GS1;1 mRNA transcripts in GS1;1-overexpressed plants can accelerate the translocation of NO3- and NH4+ from root to leaf to increase both the NO3- and NH4+ levels. The increased total levels of leaf free NO3- and NH4+ in GS1;2- and glnA-overexpressed plants could be due to the higher GS mRNA transcripts and total GS activities, which can accelerate the nitrogen absorption and reduction ability in plants.
Labs working on this gene
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China
- Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi,
Sendai 981-8555, Japan
- Metabolic Function Research Group, Plant Science Center, RIKEN, 1-7-22 Suehiro, Tsurumi-ku, Yokohama 230-0045, Japan,
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
- Avila-Ospina L, Marmagne A, Talbotec J, et al. The identification of new cytosolic glutamine synthetase and asparagine synthetase genes in barley (Hordeum vulgare L.), and their expression during leaf senescence[J]. Journal of experimental botany, 2015: erv003.
- Tabuchi M, Abiko T, Yamaya T. Assimilation of ammonium ions and reutilization of nitrogen in rice (Oryza sativa L.)[J]. Journal of Experimental Botany, 2007, 58(9): 2319-2327.
- Tabuchi M, Sugiyama K, Ishiyama K, et al. Severe reduction in growth rate and grain filling of rice mutants lacking OsGS1; 1, a cytosolic glutamine synthetase1; 1[J]. The Plant Journal, 2005, 42(5): 641-651.
- Cai H, Zhou Y, Xiao J, et al. Overexpressed glutamine synthetase gene modifies nitrogen metabolism and abiotic stress responses in rice[J]. Plant cell reports, 2009, 28(3): 527-537.