Peering into the separate roles of root and shoot cytosolic glutamine synthetase 1;2 by use of grafting experiments in Arabidopsis

Abstract

Cytosolic glutamine synthetase 1;2 plays an important role in the primary nitrogen assimilation in roots. Based on characterization of the knockout mutant gln1;2 we have recently demonstrated that Gln1;2 is also essential for ammonium handling in shoots. Here we built reciprocally grafted plants between wild type (Wt) and gln1;2 in order to separate the root and shoot roles of Gln1;2. Significant reduction in silique number and seed yield were observed in the grafted plants 1;2 shoot /Wt root relative to Wt shoot /1;2 root and Wt shoot / Wt root . Shoot Gln1;2 thus played a crucial role for seed production. Tracing experiments with 15 N showed that the relative nitrogen remobilization from vegetative organs to seeds in gln1;2 was just as efficient as in the Wt plants. This was the case although the total quantity of nitrogen in gln1;2 was significantly lower compared to that in the Wt. We conclude that the functions of shoot Gln1;2 are primarily associated with internal N signaling for establishment of seed yield capacity rather than with nitrogen remobilization.

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

“…Focusing on the reproductive stage, 15 N-tracing experiments performed by Lothier et al (2011) showed that the gln1;2 mutant was not affected in terms of N remobilization under either low- and high-nitrate conditions and it produced the same plant biomass, total seed yield, and seed C/N composition at harvest as the wild-type. The absence of defects in N remobilization was further confirmed by Guan and Schjoerring (2016) . The aim of our current study was therefore to identify which GLN1 isoforms in Arabidopsis are important for N remobilization and seed filling.…”

“… Guan et al (2015) showed that seed production and germination were impaired in the gln1;2 single and the gln1;2 - gln1;1 double knock-out mutants. As a result of grafting experiments, Guan and Schjoerring (2016) proposed that the prominent role of GLN1;2 was in the shoot; however, in their studies, Konishi et al (2017 , 2018 ) showed that both GLN1;2 and GLN1;3 are essential for ammonium assimilation in the roots.…”

Excessive assimilation of ammonium by plastidic glutamine synthetase is a major cause of ammonium toxicity in Arabidopsis thaliana

“…On the other hand, we did not determine whether shoot GLN1 isozymes attenuate or deteriorate the toxicity. With ammonium nitrate nutrition, Arabidopsis shoot GLN1;2 activity promotes shoot growth (35). We observed a larger protein signal corresponding to shoot GLN1s when plants received ammonium rather than nitrate nutrition ( SI Appendix , Fig.…”

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

“…). Guan and Schjoerring () found that GS1:2 was necessary for assimilation and detoxification of excess ammonium in Arabidopsis . While mutation of Arabidopsis GS1 : 2 gene resulted in the inhibition of the plant growth under high nitrate condition (Lothier et al.…”

“…GS1:2 was the only isoenzyme among four GS1 isoforms that was found significantly upregulated by ammonium (Ishiyama et al 2004). Guan and Schjoerring (2016) found that GS1:2 was necessary for assimilation and detoxification of excess ammonium in Arabidopsis. While mutation of Arabidopsis GS1:2 gene resulted in the inhibition of the plant growth under high nitrate condition (Lothier et al 2011).…”