Transcriptome analysis of Chlamydomonas in different iron nutritional conditions
Eugen Urzica1, Lital Adler2, David Casero3, Matteo Pellegrini3, Steven G. Clarke2, and Sabeeha Merchant1
1) Department of Chemistry and Biochemistry, UCLA
2) Department of Chemistry and Biochemistry and the Molecular Biology Institute, UCLA
3) Department of Molecular, Cell and Development Biology, UCLA
In Chlamydomonas reinhardtii four stages of iron nutrition were identified on the basis of marker gene expression, Chl content and light sensitivity: iron-excess (≥200µM Fe-EDTA) in which the cells show high-light sensitivity, growth defects and down-regulation of marker genes, iron-replete (18-20µM Fe-EDTA), iron-deficient (1-3µM Fe-EDTA) with no impact on cell growth or photosynthesis, but the genes involved in iron acquisition and homeostasis are up-regulated and iron-limited (≤ 1µM Fe-EDTA) when cell division is impaired, the cells are chlorotic indicating a defect in photosynthetic function and the genes required for Fe uptake are highly induced. To date it is clear that the amount of Fe in the medium is sensing the metal uptake but the regulator(s) of iron nutrition responses is not known. We could observe that there is a strong transcriptional component for regulation of assimilation genes and of the MSD3 gene (Page D., Allen M., Urzica E., unpublished)
In this study we applied state of the art transcriptome profiling to distinguish new targets of iron deficiency. The analysis reveals iron assimilation components and anti-oxidant pathway components (eg. Vitamin C) to be differentially regulated in response to Fe-limitation. Chlamydomonas cells grown in Fe-deficient and Fe-limited conditions show increased vitamin C levels (up to 6 fold in Fe-limitation). Transcript abundance of the Arabidopsis thaliana VTC2 homolog (catalyzing the first committed step in the ascorbic acid biosynthesis in plants) is increased in Fe-deficiency and Fe-limitation, supporting the correlation between the increased vitamin C levels and the up-regulation of the VTC2 in Fe-deprived Chlamydomonas cells.
e-mail address of presenting author: