Elsevier

Aquatic Toxicology

Volume 248, July 2022, 106202
Aquatic Toxicology

De novo transcriptome analysis reveals the molecular regulatory mechanism underlying the response to excess nitrogen in Azolla spp.

https://doi.org/10.1016/j.aquatox.2022.106202Get rights and content
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Highlights

  • Azolla species varied in tolerance to toxic stress of high nitrogen.

  • High nitrogen-tolerant species exhibited higher efficiencies for nitrogen removal.

  • Transcriptome analysis revealed the nitrogen tolerance mechanism in A. microphylla.

  • At high STN, nitrogen transport-related A. microphylla DEGs were down-regulated.

  • At high STN, nitrogen assimilation-related A. microphylla DEGs were fine-regulated.

Abstract

Phytoremediation potential of Azolla in removal of nitrogen from wastewater has been promising. However, little is known about the response of Azolla to high concentrations of nitrogen. In this study, the responses of four Azolla species to different concentrations of total nitrogen ranging from 0 to 180 mg L−1 were examined. The responses varied among different species, and the high nitrogen-tolerant species A. caroliniana and A. microphylla could remove nitrogen from aqueous solutions with higher efficiencies. We further performed transcriptome analysis to explore the molecular mechanism underlying the response to high nitrogen stress in Azolla. RNA-seq analysis revealed a synergistic regulatory network of differentially expressed genes (DEGs) involved in nitrogen transport and metabolism in A. microphylla, mainly in the roots. Under high nitrogen treatment, the DEGs encoding nitrate transporters or nitrate transporter 1/peptide transporters (NRTs/NPFs), ammonium transporters (AMTs), nitrate reductase (NIA), nitrite reductase (NIR) and glutamine synthetases/glutamate synthases (GSs/GOGATs) were down-regulated, and the DEGs encoding glutamate dehydrogenases (GDHs) were up-regulated, suggesting that A. microphylla possessed high tolerance against excess nitrogen through down-regulation of nitrate and ammonium uptake and fine regulation of nitrogen assimilation in the roots. Our results provided a theoretical foundation for better utilization of Azolla for wastewater treatment.

Keywords

Azolla
Nitrogen tolerance
Nitrogen removal
Transcriptome analysis
Nitrogen metabolism

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These authors contributed equally to this work.