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Integrated comparative transcriptome and physiological analysis reveals the mechanisms underlying genotype variations in ammonium tolerance

ABSTRACT: Several mechanisms have been proposed to explain NH4+ toxicity. However, the core information about the biochemical regulation of plants in response to ammonium toxicity is still lacking. In this study, the tissue content of NH4+was found the main cause for NH4+ toxicity, and the cellular threshold was 50 μg/g. Furthermore, ammonium led to the reprogramming of the transcriptional profile, as genes related to trehalose-6-phosphate and zeatin biosynthesis were downregulated, whereas genes related to nitrogen metabolism, camalexin, stilbenoid and phenylpropanoid biosynthesis were upregulated. Further analysis revealed that a large number of genes, which enriched in phenylpropanoid and stilbenoid biosynthesis, were uniquely upregulated in the NH4+- tolerant ecotype Or-1. These results suggested that the NH4+-tolerant ecotype showed a more intense response to ammonium by activating defense processes and pathways. Importantly, the tolerant ecotype had a higher 15NH4+ uptake and NPE, but lower NH4+, indicating the tolerant ecotype maintained a low NH4+ level, mainly by promoting ammonium assimilation rather than inhibiting NH4+ uptake. The carbon and nitrogen metabolism analysis revealed that the tolerant ecotype had a stronger carbon skeleton (2-OG) production capacity with higher levels of hexokinase (HK), pyruvate kinase (PK), and GDH activity to assimilate free NH4+. Taken together, the results revealed the threshold for ammonium toxicity and the core mechanisms utilized by plants in response to ammonium, which are consequently of ecological and agricultural importance

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE243624 | GEO | 2024/01/17

REPOSITORIES: GEO

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Project description:Algal biofuel production requires an input of synthetic nitrogen fertilizer. Fertilizer synthesized via the Haber-Bosch process produces CO2 as a waste by-product and represents a substantial financial and energy investment. Reliance on synthetic fertilizer attenuates the environmental significance and economic viability of algae production systems. To lower fertilizer input, the waste streams of algal production systems can be recycled to provide alternative sources of nitrogen such as amino acids to the algae. The halophytic green alga Dunaliella viridis can use ammonium (NH4+) derived from the abiotic degradation of amino acids, and previously, supplementation of NH4+ from glutamine (GLN) degradation was shown to support acceptable levels of growth and increased neutral lipid production compared to nitrate. To understand the effect of glutamine-released NH4+ on algae growth and physiology, metabolite levels, growth parameters, and transcript profiles of D. viridis cultures were observed in a time course after transition from media containing nitrate as a sole N source to medium containing GLN, glutamate (GLU), or a N-depleted medium. Growth parameters were similar between GLN (NH4+) and nitrate supplemented cultures, however, metabolite data showed that the GLN supplemented cultures (NH4+) more closely resembled cultures under nitrogen starvation (N-depleted and GLU supplementation). Neutral lipid accumulation was the same in nitrate and glutamine-derived NH4+ cultures. However, glutamine-derived NH4+ caused a transcriptional response in the immediate hours after inoculation of the culture. The strong initial response of cultures to NH4+ changed over the course of days to closely resemble that of nitrogen starvation. These observations suggest that release of NH4+ from glutamine was sufficient to maintain growth, but not high enough to trigger a cell transition to a nitrogen replete state. Comparative transcript profiling of the nitrogen-starved and nitrate-supplied cultures show an overall downregulation of fatty acid synthesis and a shift to starch synthesis and accumulation. The results indicate that a continuous, amino acid derived slow release of NH4+ to algae cultures could reduce the amount of synthetic nitrogen needed for growth, but optimization is needed to balance nitrogen starvation and cell division.

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Integrated comparative transcriptome and physiological analysis reveals the mechanisms underlying genotype variations in ammonium tolerance

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