PgmNr Y3112: Pdc2 and Thi3 in Candida glabrata regulate both amino acid and thiamine starvation and mediate the switch of biosynthetic capacity in response to starvation.

Authors:
C. L. Iosue; J. Nahas; D. Sens-Castet; E. Lang; D. D. Wykoff


Institutes
Villanova Univ, Villanova, PA.


Keyword: Transcription

Abstract:

Transcription factor specificity is different for some signal transduction pathways in Saccharomyces cerevisiae and Candida glabrata. For the thiamine signal transduction (THI) pathway there are a number of differences between the two species at the level of signaling and transcription. By comparing the THI pathways in the two species, we have uncovered a novel molecular switch that alters the expression of thiamine and amino acid biosynthesis genes.  In S. cerevisiae, PDC2 encodes a transcription factor that activates the transcription of both thiamine biosynthetic genes and glycolytic genes. Proper regulation of thiamine responsive genes requires the additional regulators Thi2 and Thi3. C. glabrata is missing THI2; however, C. glabrata is still capable of inducing THI genes, indicating a difference in transcriptional requirements. Deletion of ScPDC2 appears lethal in S. cerevisiae because cells are unable to utilize glucose effectively. In C. glabrata, there is no apparent growth defect in a Cgpdc2Δ strain, suggesting that Pdc2 regulates different genes between the two species. RNA-seq experiments with wild-type, Cgpdc2Δ, and Cgthi3Δ strains indicate that CgPdc2 regulates both thiamine and amino acid biosynthesis genes and not pyruvate decarboxylase genes. Interestingly, in wild-type C. glabrata, amino acid biosynthesis genes are upregulated in thiamine-replete conditions and ~10-fold repressed during thiamine starvation. This repression is lost in a Cgthi3Δ, suggesting CgThi3 plays a role in recruiting CgPdc2 to THI promoters in thiamine-limited conditions. We are exploring the altered regulation of genes by CgPdc2 by identifying the cis element(s) that CgPdc2 binds using promoter-YFP fusions with flow cytometry as well as in vitro EMSA experiments. We are also performing cross-complementation studies to determine whether CgPdc2 is capable of rescuing the lethality of the Scpdc2Δ strain. This work should uncover a novel mechanism by which C. glabrata cells partition energy to either synthesize amino acids or synthesize thiamine, using the occupancy of promoters by CgPdc2 as the switch.



Yeast Database Genetic Index
1. gene symbol: PDC2; systematic name: YDR081C
2. gene symbol: THI2; systematic name: YBR240C
3. gene symbol: THI3; systematic name: YDL080C