Apparent genetic redundancy facilitates ecological plasticity for nitrate transport

Sheila Eileen Unkles, D Zhou, MY Siddiqi, James Robertson Kinghorn, ADM Glass

Research output: Contribution to journalArticlepeer-review

67 Citations (Scopus)

Abstract

Aspergillus nidulans possesses two high-affinity nitrate transporters, encoded by the nrtA and the nrtB genes. Mutants expressing either gene grew normally on 1-10 mM nitrate as sole nitrogen source, whereas the double mutant failed to grow on nitrate concentrations up to 200 mM. These genes appear to be regulated coordinately in all growth conditions, growth stages and regulatory genetic backgrounds studied. Flux analysis of single gene mutants using (NO3-)-N-13 revealed that K-m values for the NrtA and NrtB transporters were similar to 100 and similar to 10 muM, respectively, while V-max values, though variable according to age, were similar to 600 and similar to 100 nmol/mg dry weight/h, respectively, in young mycelia. This kinetic differentiation may provide the necessary physiological and ecological plasticity to acquire sufficient nitrate despite highly variable external concentrations. Our results suggest that genes involved in nitrate assimilation may be induced by extracellular sensing of ambient nitrate without obligatory entry into the cell.

Original languageEnglish
Pages (from-to)6246-6255
Number of pages10
JournalEMBO Journal
Volume20
Issue number22
DOIs
Publication statusPublished - 15 Nov 2001

Keywords

  • Aspergillus nidulans
  • ecological plasticity
  • genetic redundancy
  • nitrate assimilation
  • nitrate transport
  • ASPERGILLUS-NIDULANS
  • CHLAMYDOMONAS-REINHARDTII
  • ARABIDOPSIS-THALIANA
  • EXPRESSION PATTERNS
  • ASSIMILATION
  • ROOTS
  • IDENTIFICATION
  • NUTRIENT
  • AMMONIUM
  • SEQUENCE

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