Abstract
Abiotic stresses such as salinity, drought and extreme temperatures affect nitrogen (N) uptake and assimilation in plants. However, little is known about the regulation of N pathway genes at transcriptional level under abiotic stress conditions in Brassica juncea. In the present work, genes encoding nitrate transporters (NRT), ammonium transporters (AMT), nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), asparagines synthetase (ASN) were cloned from Brassica juncea L. var. Varuna. The deduced protein sequences were analyzed to predict their subcellular localization, which confirmed localization of all the proteins in their respective cellular organelles. The protein sequences were also subjected to conserved domain identification, which confirmed presence of characteristic domains in all the proteins, indicating their putative functions. Moreover, expression of these genes was studied after 1h and 24h of salt (150 mM NaCl), osmotic (250 mM Mannitol), cold (4°C) and heat (42°C) stresses. Most of the genes encoding nitrate transporters and enzymes responsible for N assimilation and remobilization were found to be downregulated under abiotic stresses. The expression of BjAMT1.2, BjAMT2, BjGS1.1, BjGDH1 and BjASN2 was downregulated after 1hr, while expression of BjNRT1.1, BjNRT2.1, BjNiR1, BjAMT2, BjGDH1 and BjASN2 was downregulated after 24h of all the stress treatments. However, expression of BjNRT1.1, BjNRT1.5 and BjGDH2 was upregulated after 1h of all stress treatments, while no gene was found to be upregulated after 24h of stress treatments, commonly. These observations indicate that expression of most of the genes is adversely affected under abiotic stress conditions, particularly under prolonged stress exposure (24h), which may be one of the reasons of reduction in plant growth and development under abiotic stresses.
Highlights
Nitrogen (N) is a primary plant nutrient that plays a crucial role in determining plant growth and productivity
Our results showed that expression of some key genes involved in N-uptake and assimilation was downregulated under abiotic stress conditions
The conserved domain analysis revealed that all the NRT1 proteins contain a single proton-dependent oligopeptide transporter (PTR; PF00854) domain and NRT2 proteins contain major facilitator superfamily domain (MFS_1; PF07690) domain (Fig 2)
Summary
Nitrogen (N) is a primary plant nutrient that plays a crucial role in determining plant growth and productivity. Abiotic Stresses Downregulate Nitrogen Pathway Genes in Brassica juncea doi:10.1371/journal.pone.0143645.g001 nucleic acids and chlorophyll. The nitrogen assimilation involves reduction of nitrate to ammonium which is incorporated into amino acids by the process of ammonia assimilation (Fig 1). Several processes, including N uptake and assimilation are known to be adversely affected by abiotic stresses, such as salinity, drought, and extreme temperatures. The uptake of nitrogen, its translocation from root to shoot and its assimilation has been found to be affected by high salinity in cowpea [1]. The high salinity has been shown to inhibit the activity of many enzymes involved in nitrogen assimilation in maize, mung bean and tomato [4,5,6,7].
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