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Free keywords:
Amino Acids/metabolism
Arabidopsis/*enzymology/genetics
Carbon/metabolism
Circadian Rhythm/*physiology
Energy Metabolism/*physiology
Gas Chromatography-Mass Spectrometry
Gene Expression Profiling
Gene Expression Regulation, Enzymologic/*physiology
Genome, Plant/genetics/*physiology
Mutation/genetics
Nitrogen/metabolism
Phosphoglucomutase/genetics
RNA, Messenger/*metabolism
Abstract:
ABSTRACT: BACKGROUND: Genome-wide transcript profiling and analyses of enzyme activities from central carbon and nitrogen metabolism has shown that transcript levels undergo marked and rapid changes during diurnal cycles and after transfer to darkness, whereas changes of enzyme activities are smaller and delayed. In the starchless pgm mutant, where sugars are depleted every night, there are accentuated diurnal changes of transcript levels. Enzyme activities do not show larger diurnal changes; instead they shift towards the levels found in wild-type after several days of darkness. These results indicate that enzyme activities change slowly, integrating the changes of transcript levels over several diurnal cycles. RESULTS: To generalize this conclusion, 137 metabolites were profiled using GC-MS and LC-MS. Amplitudes of the diurnal changes of metabolites in pgm were (with the exception of sugars) similar or smaller than in wild-type. The average levels shifted towards those found after several days of darkness in wild-type. Examples include increased levels of many amino acids due to protein degradation, decreased levels of many fatty acids, increased tocopherol and decreased myo-inositol. Many metabolite-transcript correlations were found and the proportion of transcripts correlated with sugars increased dramatically in the starchless pgm mutant. CONCLUSION: Rapid diurnal changes of transcripts are integrated over time to generate quasi-stable changes across large sectors of metabolism. The slow response of enzyme activities and metabolites implies that correlations between metabolites and transcripts are due to regulation of gene expression by metabolites, rather than metabolites being changed as a consequence of a change in gene expression.
