Expression profiling reveals an unexpected growth-stimulating effect of surplus iron on the yeast Saccharomyces cerevisiae

Abstract

Iron homeostasis plays a crucial role in growth and division of cells in all kingdoms of life. Although yeast iron metabolism has been extensively studied, little is known about the molecular mechanism of response to surplus iron. In this study, expression profiling of Saccharomyces cerevisiae in the presence of surplus iron revealed a dual effect at 1 and 4 h. A cluster of stress-responsive genes was upregulated via activation of the stress-resistance transcription factor Msn4, which indicated the stress effect of surplus iron on yeast metabolism. Genes involved in aerobic metabolism and several anabolic pathways are also upregulated in iron-surplus conditions, which could significantly accelerate yeast growth. This dual effect suggested that surplus iron might participate in a more complex metabolic network, in addition to serving as a stress inducer. These findings contribute to our understanding of the global response of yeast to the fluctuating availability of iron in the environment.

Fig. 1.

The growth curve of S. cerevisiae in response to different concentration of surplus iron. The results represent three independent assays with error bars.

Fig. 2.

(A) Statistical comparisons of the transcriptomic responses upon 5 mM Fe³⁺. Black bars indicate genes that strongly responded (≥ 2.0-fold), whereas gray bars indicate genes that weakly responded (1.5∼2.0-fold). (B) Venn diagrams of up-regulated genes and down-regulated genes of S. cerevisiae upon surplus iron in 1 h versus 4 h. The genes are shown here whose transcriptional level changed more than 2.0-fold.

Fig. 3.

The relative amounts of mRNA of MSN2/MSN4 determined by RT-PCR (A) and qRT-PCR (B) upon different concentration of surplus iron. The transcription of MSN4 was increased dependent on iron concentration, while MSN2 was not. β-ACTIN (house-keeping gene) was as internal control. The results represent three independent assays with error bars.

Fig. 4.

(A) Subcellular localization of Msn4 upon surplus iron. The fluorescence was monitored by GFP that is fused with Msn4. (B) DAPI staining control. (C) The dynamic distribution of Msn4 upon surplus iron captured at an interval of 20 s.

Fig. 5.

Schematic representation of the dual effect of responses in yeast upon surplus iron. Red down-arrow indicates the downregulated genes and Green up-arrow indicates the upregulated genes. Stress-responsive genes can be mediated by Msn4 and other unknown transcription factors; Growth-stimulating genes can also be mediated by certain transcription factors such as Gcn4 (regulating amino acid biosysthesis gene LEU1), Mcm1 (regulating cell mating gene STE3) and Pip2 (regulating lipid biosysthesis gene FAA1).