# Mitochondrial Translation Inhibition Triggers an Rst2-Controlled Transcriptional Reprogramming of Carbon Metabolism in Stationary-Phase Cells of Fission Yeast

## TL;DR

When mitochondrial translation is blocked in fission yeast, cells reprogram their carbon metabolism through a stress-like response controlled by the Rst2 transcription factor.

## Contribution

The study reveals a novel transcriptional reprogramming mechanism in stationary-phase fission yeast cells under mitochondrial translation inhibition.

## Key findings

- CAP-treated stationary-phase cells in glucose medium showed a strong transcriptome response resembling stress and retrograde responses.
- Rst2 and Scr1 regulate carbon metabolism genes and opposingly affect cell lifespan in CAP-treated stationary-phase cells.
- Rst2 maintains nuclear localization and is essential for inducing carbon metabolism genes under mitochondrial dysfunction.

## Abstract

Mitochondria possess their own genome, which encodes subunits of the electron transport chain, rendering mitochondrial protein translation essential for cellular energy metabolism. Mitochondrial dysfunction affects nuclear transcription through the retrograde response. We applied RNA-seq to investigate whether and how the inhibition of mitochondrial translation by chloramphenicol (CAP) affects transcriptome regulation in proliferating or stationary-phase cells of Schizosaccharomyces pombe growing in fermentative or respiratory media. Stationary-phase cells in glucose medium exhibited the strongest transcriptome response to CAP, characterized by expression signatures similar to those observed under other stresses, including the retrograde response. The induced genes were also significantly enriched in cytoplasmic carbon metabolism pathways, reflecting a transcriptional reprogramming from respiration to fermentation. The transcription factors Scr1 and Rst2, regulators of carbon catabolite repression (CCR), controlled a common set of carbon metabolism genes in CAP-treated stationary-phase cells, and they showed opposing effects on the lifespan of these cells. Rst2 was required for the induction of carbon metabolism genes and maintained nuclear localization in CAP-treated stationary-phase cells. A systematic genetic interaction screen revealed functional relationships of Rst2 with processes related to stress and starvation responses. These findings uncover a complex transcriptional program in stationary-phase cells that adapt to inhibited mitochondrial translation, including stress- and retrograde-like responses, contributions of the CCR factors Scr1 and Rst2, and adjustment of carbon metabolism to deal with mitochondrial dysfunction.