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UNRAVELING THE REGULATION OF NITROGEN ASSIMILATION IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE): DIURNAL VARIATIONS IN TRANSCRIPT LEVELS FOR FIVE GENES INVOLVED IN NITROGEN ASSIMILATION 1
Author(s) -
Brown Kathryn L.,
Twing Katrina I.,
Robertson Deborah L.
Publication year - 2009
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.2009.00648.x
Subject(s) - thalassiosira pseudonana , biology , glutamine synthetase , nitrogen assimilation , diatom , nitrite reductase , chloroplast , nitrate reductase , gene , biochemistry , botany , enzyme , glutamine , nutrient , phytoplankton , ecology , amino acid
We examined the diurnal expression of five genes encoding nitrogen‐assimilating enzymes in the marine diatom Thalassiosira pseudonana (Hust.) Hasle et Heimdal following a transition from NH 4 + ‐ to NO 3 − ‐supplemented media. The accumulation of nia transcripts (encoding nitrate reductase, NR) following the transition to NO 3 − ‐supplemented media was similar to previously reported changes in NR abundance and activity. Nia mRNA levels varied diurnally, and the diurnal oscillations were abolished when cells were transferred to continuous light. Genes encoding chloroplastic ( nii A) and cytosolic ( nir B) nitrite reductases were identified in the genome of T. pseudonana . Nii A and nir B transcript levels increased within 2 h following the addition of NO 3 − and varied diurnally. Patterns of diurnal variation in nia , nii A, and gln II (encoding the chloroplast‐localized glutamine synthetase) mRNA abundances were similar. Nir B and gln N (encoding the cytosolic‐localized glutamine synthetase) mRNA levels also oscillated diurnally; however, the oscillation was out of phase with nia , nii A, and gln II. We propose that NO 3 − is assimilated into organic molecules in both the chloroplast and cytosol of diatoms and that enzymes encoded by nir B and gln N contribute to the ecologically important dark assimilation of NO 3 − observed in marine diatoms. As with nia , the diurnal variations in nii A, nir B, gln II, and gln N were abolished when cells were transferred to continuous light. Our results demonstrate that transcript accumulation is not circadian controlled, but, rather, changes in metabolic pools triggered by light:dark (L:D) transitions may be important in regulating the cellular mRNA levels encoding these key nitrogen assimilating enzymes.