Three cytosolic glutamine synthetase isoforms localized in different-order veins act together for N remobilization and seed filling in Arabidopsis

J. Plant Nutr. Soil Sci.

Tang

et al. 2020

The contribution of N remobilization is crucial for new shoots growth and quality formation during spring tea shoots development. However, the translocation mechanism of N from source leaves to sink young shoots is not well understood. In the present study, 15N urea was applied to mature tea leaves one week before bud break to track N remobilization in a field experiment. The dynamic changes in plant 15N abundance, contents of amino acids, and the expression levels of genes related to N metabolism and translocation were followed during the 18‐d development of new spring shoots until three expanding young leaves. The results showed that during the growth of new shoots the amount of 15N in the shoots increased, whereas the Ndff (N derived from 15N‐urea) in mature leaves decreased, showing that the foliar‐applied N in mature leaves was readily exported to new shoots. This process was found to be accompanied by decline of chlorophylls. In the mature leaves, expression CsATG18a and CsSAG12 involved in autophagy was dramatically induced (> 4‐fold) at approximately nine days after the bud breaking. The genes involved in the transformation of amino acids, including primarily CsGDH2, CsGDH4, CsGLT3, CsGS1;3, and CsASN2 were upregulated by > 3‐fold after bud breaking. The expression levels of CsATG8A, CsATG9, CsSAG12, CsGS1;1, CsGDH1, and CsAAP6 correlated negatively with the Ndff in mature leaves, but positively with 15N amount and total N amount in new shoots, suggesting these genes played important roles in N export from mature leaves. In the new shoots, the expression of most genes showed two defined peaks, one on six days and one on 12 days after bud breaking. The expression of CsGS2, CsASN3, CsGLT1, and CsAAP4 positively correlated with the 15N amount and total N amount in new shoots. These genes might be involved in the transport and re‐assimilation of N from mature leaves. The overall results demonstrated that the translocation of 15N from mature leaves to new spring shoots was regulated by the genes involved in autophagy, protein degradation, amino acid transformation and transport.

Section: Introductionmentioning

confidence: 99%

Dynamics of nitrogen translocation from mature leaves to new shoots and related gene expression during spring shoots development in tea plants (Camellia sinensis L.)

Fan

J. Plant Nutr. Soil Sci.

Tang

et al. 2020

“…In Arabidopsis, GS1 is encoded by five individual isogenes with distinct affinities for NH 4 + and glutamate and tissue localization as well as distinct physiological functions (Guan et al , 2016; Guan et al , 2015; Ishiyama et al , 2004b; Konishi et al , 2017; Lothier et al , 2011; Moison et al , 2018). Phylogenetically, the nucleotide and amino acid sequences of these isoforms do not cluster with GS1 sequences from cereals (Thomsen et al , 2014).…”

Section: Introductionmentioning

confidence: 99%

How do three cytosolic glutamine synthetase isozymes of wheat perform N assimilation and translocation?

Wei

Wang

et al. 2019

Preprint

To understand how the three cytosolic glutamine synthetase (GS1) isozymes of wheat (Triticum aestivum L., TaGS1) perform nitrogen assimilation and translocation, we studied the kinetic properties of TaGS1 isozymes, the effects of nitrogen on the expression and localization of TaGS1 isozymes with specific antibodies, and the nitrogen metabolism. The results showed TaGS1;1, the dominant TaGS1 isozyme, had a high affinity for substrates, and was widely localized in the mesophyll cells, root pericycle and root tip meristematic zone, suggesting it was the primary isozyme for N assimilation. TaGS1;2, with a high affinity for Glu, was activated by Gln, and was mainly localized in the around vascular tissues, indicating that TaGS1;2 catalyzed Gln synthesis in low Glu concentration, then the Gln returned to activate TaGS1;2, which may lead to the rapid accumulation of Gln around the vascular tissues. TaGS1;3 had low affinity for substrates but the highest Vmax among TaGS1, was mainly localized in the root tip meristematic zone; exogenous NH4+ could promote TaGS1;3 expressing, indicating that TaGS1;3 could rapidly assimilate NH4+ to relieve NH4+ toxicity. In conclusion, TaGS1;1, TaGS1;2 and TaGS1;3 have different role in N assimilation, Gln translocation and relieving ammonium toxicity, respectively, and synergistically perform nitrogen assimilation and translocation.HighlightThree cytosolic glutamine synthase isozymes of wheat have different role and synergistically perform nitrogen assimilation and translocation.

“…Moison et al. () demonstrated that the function of GS1:1, GS1:2, and GS1:3 could compensate each other in Arabidopsis while the gene expression and activity of chloroplastic GS2 in the diatom Thalassiosira pseudonana was stimulated by the presence of nitrate in the medium, but not ammonium (Glibert et al. ).…”

mentioning

confidence: 99%

“…The GS family contains GSI, GSII, and GSIII groups based on the molecular size and the number of subunits (Ghoshroy et al 2010). The number, expression, and function of GSII isoenzymes were most widely studied in higher plants and microalgae (Glibert et al 2016, Moison et al 2018, N emeth et al 2018, Wang et al 2018a. It was known that GSII consists of cytosolic GS1 and chloroplastic GS2 isoenzymes (Diaz et al 2008).…”

mentioning

confidence: 99%

“…While mutation of Arabidopsis GS1:2 gene resulted in the inhibition of the plant growth under high nitrate condition (Lothier et al 2011). Moison et al (2018) demonstrated that the function of GS1:1, GS1:2, and GS1:3 could compensate each other in Arabidopsis while the gene expression and activity of chloroplastic GS2 in the diatom Thalassiosira pseudonana was stimulated by the presence of nitrate in the medium, but not ammonium (Glibert et al 2016). GS2 has already become a genetic marker for nitrate assimilation in diatom Skeletonema costatum (Allen et al 2006).…”

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confidence: 99%

See 1 more Smart Citation

Glutamine Synthetase (GS): A Key Enzyme for Nitrogen Assimilation in The Macroalga Gracilariopsis lemaneiformis (Rhodophyta)

Liu

Huan

et al. 2019

Journal of Phycology

This study aimed to address the importance of glutamine synthetase II (GSII) during nitrogen assimilation in macroalga Gracilariopsis lemaneiformis. The cDNA full‐length sequence of the three glGSII genes was revealed to have the 5′ m7G cap, 5′‐untranslated region, open reading frame (ORF), 3′‐untranslated region, and a 3′ poly (A) tail. The three glGSIIs were classified into plastid glGS2 and cytosolic glGS1‐1 and glGS1‐2, having conserved GSII domains but different cDNA sequences. The complicated 5′ end flanking region indicates complex function of glGS genes. glGS1 genes were significantly up‐regulated under the different NH4+: NO3− ratio (i.e., 40:10, 25:25, 10:40, and 0:50) except glGS2 which dramatically up‐regulated under the low NH4+: NO3− ratio (i.e., 10:40 and 0:50) during different cultivation times. These different expression patterns perhaps are due to the different biological roles of GS1 and GS2 in the gene family. Furthermore, hypothetical working model of nitrogen assimilation pathway exhibiting the role of glGS1 and glGS2 is proposed. Finally, glGS2 was expressed in Escherichia coli BL21 (DE3), and the optimal conditions for culture (15°C, overnight), purification (500 mM imidazole washing), and activity (pH 7.4, 37°C) were established. This study lays a very important foundation for exploring the role of GS in nitrogen assimilation in algae and plants.