Nitrite transport is mediated by the nitrite-specific high-affinity NitA transporter and by nitrate transporters NrtA, NrtB in Aspergillus nidulans

Wang, Ye; Li, Wenbin; Siddiqi, Yaeesh; Symington, Vicki F.; Kinghorn, James R.; Unkles, Shiela E.; Glass, Anthony D. M.

doi:10.1016/j.fgb.2007.10.001

Cited by 30 publications

(42 citation statements)

References 25 publications

(49 reference statements)

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“…The gene forms a putative operon with the NiR structural gene nirA, except in Synechococcus sp. strain PCC7002, and the deduced protein is similar to the nitrite transporters from the green alga Chlamydomonas reinhardtii (40), the fungus Aspergillus nidulans (49), and Escherichia coli (8), strongly suggesting that it has a role in nitrite transport (41), although a functional characterization of the gene has yet to be performed.…”

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confidence: 97%

“…strain PCC7002, which has NrtP and a FocA-like transporter that presumably transport nitrite (41), and the significance of cynABD in nitrite transport is unclear. FocA-like proteins involved in nitrite transport have been identified in C. reinhardtii (40), Aspergillus nidulans (49), and E. coli (8), and the K s (NO 2 Ϫ ) or K m (NO 2 Ϫ ) of the transporter has been estimated to be 5 M in C. reinhardtii (40) and 4 M in A. nidulans (49). Their homologs are found in many marine cyanobacterial strains, forming a putative operon with the NiR structural gene nirA, except in Synechococcus sp.…”

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confidence: 99%

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Nitrite Transport Activity of the ABC-Type Cyanate Transporter of the Cyanobacterium Synechococcus elongatus

Maeda

Omata

2009

J Bacteriol

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In addition to the ATP-binding cassette (ABC)-type nitrate/nitrite-bispecific transporter, which has a high affinity for both substrates (K m , ϳ1 M), Synechococcus elongatus has an active nitrite transport system with an apparent K m (NO 2 ؊ ) value of 20 M. We found that this activity depends on the cynABD genes, which encode a putative cyanate (NCO ؊ ) ABC-type transporter. Accordingly, nitrite transport by CynABD was competitively inhibited by NCO ؊ with a K i value of 0.025 M. The transporter was induced under conditions of nitrogen deficiency, and the induced cells showed a V max value of 11 to 13 mol/mg of chlorophyll per h for cyanate or nitrite, which could supply ϳ30% of the amount of nitrogen required for optimum growth. Its relative specificity for the substrates and regulation at transcriptional and posttranslational levels suggested that the physiological role of the bispecific cyanate/nitrite transporter in S. elongatus is to allow nitrogendeficient cells to assimilate low concentrations of cyanate in the medium. Its contribution to nitrite assimilation was significant in a mutant lacking the ABC-type nitrate/nitrite transporter, suggesting a possible role for CynABD in nitrite assimilation by cyanobacterial species that lack another high-affinity mechanism(s) for nitrite transport.

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confidence: 97%

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Nitrite Transport Activity of the ABC-Type Cyanate Transporter of the Cyanobacterium Synechococcus elongatus

Maeda

Omata

2009

J Bacteriol

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“…Perhaps surprisingly, given that NNP and certain FNT proteins share the same substrate, nitrite, the crucial conserved arginine residues that bind nitrate in NNP proteins (35) are not present in the FNT group of transporters. Previous 13 NO 3 Ϫ tracer studies showed that wild-type strains of A. nidulans possess two high-affinity nitrate transporters (NrtA and NrtB) that, in common with high-affinity nitrate transporters from other organisms (8), also transport nitrite (40). Mutant strains lacking NrtA and NrtB showed no 13 NO 3 Ϫ tracer uptake yet are capable of growth on nitrite and a net uptake of nitrite (40).…”

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“…Phytoplankton has been shown to excrete significant amounts of nitrite when nitrate uptake exceeds the capacity for the assimilation of the nitrite generated (20). Conditions such as low light, low temperature, or a disruption of the nitrate reductase activity (40) may result in nitrite efflux that matches nitrate uptake in a 1:1 stoichiometry. This nitrite may subsequently be taken up and converted to ammonium by assimilatory nitrite reductase, followed by assimilation into organic nitrogenous compounds within root plastids or chloroplasts (2).…”

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confidence: 99%

“…These transporters include Escherichia coli EcNirC (3,12,13), Aspergillus nidulans AnNitA (40), and C. reinhardtii CrNar1, which possesses no fewer than six paralogs (18,23). Such proteins belong to a family quite separate from the MFS, known as the formate/ nitrite transporter (FNT) family (TC 2.A.44), and many FNT members are thought to transport nitrite and/or the structurally related formate.…”

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Physiological and Biochemical Characterization of AnNitA, the Aspergillus nidulans High-Affinity Nitrite Transporter

et al. 2011

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High-affinity nitrite influx into mycelia ofAlthough nitrate and ammonium are the major sources of nitrogen for bacteria, fungi, algae, and plants, nitrite may also represent a significant nitrogen source under some circumstances. For example, in waterlogged anaerobic soils as well as in aerobic soils where gaseous anaerobic pockets exist, substantial levels of nitrite may accumulate (14). Phytoplankton has been shown to excrete significant amounts of nitrite when nitrate uptake exceeds the capacity for the assimilation of the nitrite generated (20). Conditions such as low light, low temperature, or a disruption of the nitrate reductase activity (40) may result in nitrite efflux that matches nitrate uptake in a 1:1 stoichiometry. This nitrite may subsequently be taken up and converted to ammonium by assimilatory nitrite reductase, followed by assimilation into organic nitrogenous compounds within root plastids or chloroplasts (2). As well as being a source of nitrogen for a range of organisms, there are associated agricultural, environmental, and even medical issues involved in nitrite biogeochemistry (16,37).There is a substantial amount of information available for the nitrite assimilatory enzyme system, nitrite reductase, as well as certain nitrate uptake systems that also transport nitrite as well as nitrate. These bispecific permeases (together with those that transport nitrate only, such as Chlamydomonas reinhardtii NRT2.2) are characterized by 12 transmembrane ␣-helical domains (Tms), a nitrate signature, and a major facilitator superfamily (MFS) motif and belong to the nitrate NNP (nitrate nitrite porter) subgroup (TC 2.A.1) of the MFS (21,25,33).In contrast, there are transporters that transport nitrite but not nitrate, for which much less is known. These transporters include Escherichia coli EcNirC (3, 12, 13), Aspergillus nidulans AnNitA (40), and C. reinhardtii CrNar1, which possesses no fewer than six paralogs (18, 23). Such proteins belong to a family quite separate from the MFS, known as the formate/ nitrite transporter (FNT) family (TC 2.A.44), and many FNT members are thought to transport nitrite and/or the structurally related formate. FNT family members are found in the microbial kingdoms of archaea, eubacteria, protista, and fungi. Most members of the FNT family probably possess 6 Tms and are much smaller (at the primary protein sequence level) than NNP proteins. For example, the A. nidulans AnNitA protein possesses 310 amino acid residues, compared to the AnNrtA high-affinity nitrate transporter, which has 507 amino acid residues. Recently, a structural analysis of the purified FocA proteins (members of the FNT family) from E. coli (7,41) and Vibrio cholerae (38) suggested that these proteins are pentameric formate channels, with each FocA subunit being made up of six transmembrane ␣-helices. FocA channels, with affinities for formate that may be in the millimolar to tens of millimolar range (38), are thought to export formate generated from pyruvate during anaerobic respiration. The extent ...

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Nitrate assimilation pathway (NAP): role of structural (nit) and transporter (ntr1) genes in Fusarium oxysporum f.sp. lycopersici growth and pathogenicity

et al. 2017

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The tomato pathogen Fusarium oxysporum f.sp. lycopersici possesses the capability to use nitrate as the only nitrogen source under aerobic and anaerobic conditions and to activate virulence-related functions when cultivated in the presence of nitrate, but not in ammonium. The genome of F. oxysporum f.sp. lycopersici encodes three paralogs nitrate reductase (NR) genes (nit1, nit2 and nit3) and one predicted ortholog of the Aspergillus nidulans high-affinity nitrate/nitrite transporters NtrA and NtrB, named ntr1. We set out to clarify the role of nit1, nit2, nit3 and ntr1 genes in nitrate assimilation and in the virulence of F. oxysporum f.sp. lycopersici. Quantitative RT-PCR analysis revealed that only nit1, nit2 and ntr1 are expressed at significant levels during growth in nitrate as the only nitrogen source. Targeted deletion of nit1 and ntr1, but not of nit2 or nit3, severely impaired growth of F. oxysporum on nitrate as nitrogen source, indicating that Nit1 and Ntr1 proteins are involved in nitrate assimilation by the fungus; biochemical analysis of nit mutants indicated that Nit1 and Nit2 enzymes contribute to about 50 and 30% of the total NR activity, respectively. In addition, a spontaneous chlorate-resistant mutant derived from F. oxysporum 4287, denoted NitFG, was characterized, showing inability to grow in nitrate under aerobic and anaerobic conditions and low levels of NR activity, in spite of its increased transcription levels of nit1 and nit2 genes. Tomato plant infection assays showed that NitFG and ∆ntr1 mutants induced an earlier death in tomato plants, whereas the single mutants ∆nit1, ∆nit2 and ∆nit1∆nit2 double mutant showed a mortality rate similar to the wild-type strain. Taken together, these results indicate that the Nit1 and Ntr1 proteins are important for nitrate assimilation of F. oxysporum f.sp. lycopersici incubated under aerobic and anaerobic conditions and that this metabolic process is not essential for the virulence of the fungus. These observations open new questions about the role of Nit1, Nit2, and Nit3 proteins in other routes of nitrate metabolism in this pathogenic fungus and in the possible regulatory role that can be exerted by the AreA protein in these routes.

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Nitrite transport is mediated by the nitrite-specific high-affinity NitA transporter and by nitrate transporters NrtA, NrtB in Aspergillus nidulans

Cited by 30 publications

References 25 publications

Nitrite Transport Activity of the ABC-Type Cyanate Transporter of the Cyanobacterium Synechococcus elongatus

Nitrite Transport Activity of the ABC-Type Cyanate Transporter of the Cyanobacterium Synechococcus elongatus

Physiological and Biochemical Characterization of AnNitA, the Aspergillus nidulans High-Affinity Nitrite Transporter

Nitrate assimilation pathway (NAP): role of structural (nit) and transporter (ntr1) genes in Fusarium oxysporum f.sp. lycopersici growth and pathogenicity

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