Evidence for post-translational regulation of NrtA, the Aspergillus nidulans high-affinity nitrate transporter.
Here, influx and efflux of (13)NO(3)(-), and net fluxes of (14)NO(3)(-) and (14)NO(2)(-), were measured in Aspergillus nidulans mutants niaD171 and niiA5, devoid of nitrate reductase (NR) and nitrite reductase (NiR) activities, respectively. Transcript and protein abundances of NrtA, the A. nidulans principal high-affinity NO(3)(-) transporter, were determined using semiquantitative reverse transcription-polymerase chain reaction and western blots, respectively. (13)NO(3)(-) influx in niaD171 was negligible relative to wild-type values, whereas efflux to influx ratios increased nine-fold. Nevertheless, NrtA mRNA and NrtA protein were expressed at levels more than two-fold and three-fold higher, respectively, in niaD171 than in the wild-type strain. This is the first demonstration of diminished high-affinity NO(3)(-) influx associated with elevated transporter levels, providing evidence that, in addition to transcriptional regulation, control of NrtA expression operates at the post-translational level. This mechanism allows for rapid control of NO(3)(-) transport at the protein level, reduces the extent of futile cycling of NO(3)(-) that would otherwise represent a significant energy drain when influx exceeds the capacity for assimilation or storage, and may be responsible for the rapid switching between the on and off state that is associated with simultaneous provision of NH(4)(+) to mycelia absorbing NO(3)(-).
Wang
Ye
Y
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
Li
Wenbin
W
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
Siddiqi
Yaeesh
Y
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
Kinghorn
James R
JR
School of Biology, University of St Andrews, St Andrews KY16 9TH, UK.
Unkles
Shiela E
SE
School of Biology, University of St Andrews, St Andrews KY16 9TH, UK.
Glass
Anthony D M
ADM
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
D027321:Anion Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D001233:Aspergillus nidulans / Q000235:genetics* / Q000378:metabolism; D001693:Biological Transport, Active; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D009154:Mutation; D009566:Nitrates / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D027321:Anion Transport Proteins; D005656:Fungal Proteins; D009566:Nitrates; D009589:Nitrogen Oxides; C444100:NrtA protein, Aspergillus nidulans; D012331:RNA, Fungal; D012333:RNA, Messenger; C031701:nitrogen trioxide
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